RE: Finding hidden backdoors

["Michael Silk" <michaels () phg com au>]

Well backdoors don't always have to have a port open waiting
for connections, one such different variation could be:
        - backdoor runs every X o'clock, connecting to a website
                to receive its malicious commands ... hence it will
                just look like a simply http browsing session and
                will probably be un-noticed.

        A simple port-search wouldn't pick that up :)

-- Michael

-----Original Message-----
From: Tim Greer [mailto:chatmaster () charter net]
Sent: Friday, 1 August 2003 8:26 AM
To: Daniel B. Cid; security-basics () securityfocus com
Subject: Re: Finding hidden backdoors


The backdoor could easily only accept connections from non local sources, or
a specific source.  It's probably easier to just run netstat, lsof, etc.
from a clean. trusted media... or also boot into single user mode from a
trusted kernel image.  In fact, you should always have trusted kernel images
on the server anyway, for purposes of being able to boot if the other image
is corrupted or modified.  As for LKM, I don't compile with lkm support in
my kernels for many reasons (security being one of them), but a lot of
people do, so...
--
Regards,
Tim Greer  chatmaster () charter net
Server administration, security, programming, consulting.


----- Original Message -----
From: "Daniel B. Cid" <danielcid () yahoo com br>
To: <security-basics () securityfocus com>
Sent: Thursday, July 31, 2003 1:18 PM
Subject: Finding hidden backdoors


> I saw some people talking about rootkits that hidden process/ports.
> One think that i always do to see what ports are open is to run this
> perl script:
>
>
> use IO::Socket;
> for($i=0;$i<=65555;$i++)
>         {
>         $server[$i] = IO::Socket::INET->new(
>         Proto => 'tcp',
>         LocalPort => $i,
>         Listen => SOMAXCONN,
>         Reuse => 1) or print "Port $i Open \n" unless $server[$i];
>         close ($server[$i]);
>         }
>
> This is good because if "netstat" or "lsof" or "fuser" or any other
> program is trojaned , or if it has any firewall and nmap is not finding
> all the open ports, this script will show ... The other benefit is that
> you cant hidden from it using any LKM code...
> What do you thing ?
>
> thanks
>
> Daniel B. Cid
>
>
>
>
>
>
> --------------------------------------------------------------------------
-
> --------------------------------------------------------------------------
--
>


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