Follow @Openwall on Twitter for new release announcements and other news
[<prev] [next>] [<thread-prev] [thread-next>] [day] [month] [year] [list]
Date: Wed, 5 Mar 2008 10:19:09 +0100
From: Tomas Hoger <thoger@...hat.com>
To: oss-security@...ts.openwall.com
Subject: Re: request CVE id: insecure handling of DISPLAY in
 rxvt

On Tue, 4 Mar 2008 22:34:10 +0000 Steve Kemp <steve@...ve.org.uk> wrote:

>   The idea is that if you typically connect to a host with display
>  forwarding you'll be used to running rxvt and having the resulting
>  application display locally.
> 
>   However if you forget to enable display forwarding then run
>  RXVT it will connect to :1, rather than complain there is no
>  DISPLAY set and abort.  That *could* allow a malicious local
>  server to steal keyboard, & etc.
> 
>   However I have a hard time seeing this in practise.  It would
>  mean that locally you couldn't trust root - since it would take
>  a local root user to setup the fake X11 server on :1..

I don't think you need root privileges to take advantage of this...

Let's assume shared box where users ssh -X and run some X programs,
e.g. rxvt.  Let's assume unprivileged user can start local X session
which will be DISPLAY=:0 and do xhost + to allow connections from other
users to her display (maybe Xvnc can be used instead of local X session
too).  Now she just have to wait for some other user to ssh without X
forwarding and start rxvt on her display.

Yes, many assumptions and ifs, but still silently assuming DISPLAY=:0
when no DISPLAY is set does not sound like a safe default.

Just my 2c.

-- 
Tomas Hoger
Red Hat Security Response Team

Powered by blists - more mailing lists

Please check out the Open Source Software Security Wiki, which is counterpart to this mailing list.

Confused about mailing lists and their use? Read about mailing lists on Wikipedia and check out these guidelines on proper formatting of your messages.