Gentoo Archives: gentoo-security

From: Brian Micek <bmicek@×××××××××.net>
To: gentoo-security@l.g.o
Subject: [gentoo-security] SSH probes
Date: Sat, 05 Nov 2005 20:03:36
Message-Id: 1131220618.8882.78.camel@localhost.localdomain
I don't mean to re-start an old topic, but would anyone happen to have
access to the source code for the second phase of the popular SSH
probes?  The reason I'm interested in it is because I'd like to exploit
some weaknesses in the code and at least cause it to drop a core.

Currently, I have a service started by xinetd and close stdin on the
command line arguments to avoid hackers hacking my program.  I run a
bash script as user "nobody" that basically looks like this (extra
extraneous stuff is removed):

#!/bin/bash
function fakessh() {
  echo SSH-2.0-OpenSSH_3.9p1 # ID ourself as a valid SSH service
  /bin/cat /dev/urandom # and send random data
}
# Main follows - this is run as user "nobody"
fakessh <&-  # Call the payload and (again) close stdin to avoid hacks
# EOF - fakessh

The result for someone using a normal ssh client is:
UNIX>  ssh localhost
Disconnecting: Bad packet length 3349376822.

I am hoping to cause some kind of memory problem here and thats why I
need the source code.  Another exploit to examine is what happens with
zero length packets if we cat /dev/zero.  If there is nothing to exploit
here, I'll remove the "echo" line so I send random data until the hacker
client terminates his connection.

Thank you,
Brian Micek

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Replies

Subject Author
Re: [gentoo-security] SSH probes William Yang <wyang@××××.net>