Bugtraq mailing list archives
SSH & xauth
From: cazz () RUFF CS JMU EDU (Brian Caswell)
Date: Thu, 24 Feb 2000 17:31:35 -0500
The default SSH configuration for SSH1 and SSH2 allow for remote controlling of X sessions through X forwarding. All children of the SSH connection are able to tunnel X11 sessions through the X tunnel to the client X11 session. This is accomplished by running xauth upon logging in. If xauth is replaced on the server by a malicious program that does both of the following: - runs xauth, adding in the "correct" information allowing the children of the session to tunnel X11 programs through the SSH session - runs xauth, adding in the "malicious" information, allowing a malicious source to tunnel X11 programs through the SSH session. With the added data in .Xauthority, a malicious source can fully control the client X session. The malicious source can then do most anything to the X session, from logging keystrokes of the X session, to taking screen captures, to typing in commands to open terminals. The only thing that is required for the client system to be compromised is for the client to remotely log via ssh (with X11 forwarding enabled) into a compromised server. Allowing X forwarding seems to be turned on by default in SSH1, SSH2, and OpenSSH. To fix this "issue" add the following lines to the SSH client configuration. ($HOME/.ssh/config or ssh_config) Host * ForwardX11 no Discussions of security flaws within X11 have been going on for years. The "issue" in SSH X11 forwarding is not new. SSH has added to the security of X11, but by no means does the use of SSH secure X11. -- Brian Caswell <cazz () ruff cs jmu edu> If I could load the world into vi, the first command I would use is: %s/Windows NT//gi <HR NOSHADE> <UL> <LI>application/pgp-signature attachment: stored </UL>
Current thread:
- SSH & xauth Brian Caswell (Feb 24)
- Re: SSH & xauth Andrey (Feb 25)
- Re: SSH & xauth David Terrell (Feb 25)
- Re: SSH & xauth Robert Watson (Feb 25)
- Re: SSH & xauth Lionel Cons (Feb 28)
- Re: SSH & xauth David Pybus (Feb 26)
- Re: SSH & xauth Robert Watson (Feb 28)
- xterm log file vulnerability Morten Welinder (Feb 29)
- false alarms by real secure Danton Nunes (Feb 29)
- New ZZ Posted Simple Nomad (Feb 29)
- DOS in Trendmicro OfficeScan cerberus (Feb 26)
(Thread continues...)