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Date: Tue, 22 Feb 2011 17:31:05 +0100
From: Thomas Biege <>
Subject: gdm PostLogin script executes scripts as user gdm

Hello oss-security,

should we consider this as a vulnerability?

ericlesoll [reporter] 2009-11-19 13:00:11 UTC

on Ubuntu Karmic Koala and Fedora 12
After a fresh install on some machines and update from Jaunty on another one,
we can't catch $USER $USERNAME $LOGNAME
from /etc/gdm/PostLogin/Default, we get "gdm" for all variables instead of real
login name. It was working since 7.04 version.
If in a terminal we run : echo $USER, we get the real login name.

example below :

If I put those 3 lines in /etc/gdm/PostLogin/Default:

echo $USER > /tmp/aaa.txt
echo $USERNAME >> /tmp/aaa.txt
echo $LOGNAME >> /tmp/aaa.txt

after every login I get this result:

$ cat /tmp/aaa.txt

I would expect to get my real login name in those 3 variables instead of "gdm",
which is of no use to take specific action based on which user is logging in.
This was working as expected with at least the 3 previous versions of Ubuntu.


 Thomas Biege <>, SUSE LINUX, Security Support & Auditing
 SUSE LINUX Products GmbH, GF: Markus Rex, HRB 16746 (AG Nuernberg)
  Wer aufhoert besser werden zu wollen, hoert auf gut zu sein.
                            -- Marie von Ebner-Eschenbach

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