Any local user can destroy X service by moving (or deleting) the UNIX domain socket redhat puts in /tmp/.X11-unix/X0 . Redhat apparently forgot the sticky bit. I think this works in Redhat 4.0 too.
Carlo Wood <carlo@RUNAWAY.XS4ALL.NL>
Screw up X (local)
Thos running the Redhat 4.2 and 4.0 Linux distributions.
14 November 1997
Date: Fri, 14 Nov 1997 02:13:22 +0100
From: Carlo Wood <carlo@RUNAWAY.XS4ALL.NL>
Subject: X Security problem (?)
this isn't an exploit - I let others write that ;) (don't
have time for that).
But five minutes ago I found something that might be abused:
On my (RedHat4.2) linux box, I find:
A UNIX domain socket of the X server I assume.
The permissions are:
drwxrwxrwt 3 root root 1024 Nov 14 01:38 /tmp/
drwxrwxrwx 2 root users 1024 Nov 14 01:56 /tmp/.X11-unix/
srwxrwxrwx 1 root users 0 Nov 13 23:09 X0
So, as any user (I did it as 'nobody'), I can do:
After which X doesn't work anymore (can't open a new terminal).
I can also do:
mv X0 Y0
(can't open an xterm)
mv Y0 X0
(everything works again).
Now I didn't test the following, but doesn't this mean that I can
- as nobody - mv X0 Y0; open a new X0 socket and start to accept
connections, piping everything to Y0, reading everything people
type, like passwords when they use 'su' ? ...
PS This is my first post, so I expect to make a terrible error
here somehow ;). If so, I hope the moderator will simply
refuse the post.
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