Secure testing team - Aug 2011 - Bug#639151: Local privilege escalation

Package: lightdm
Severity: grave
Tags: security

Sebastian Kramer posted the following to oss-security:

---

From: Sebastian Krahmer <krahmer at suse.de>
To: oss-security at lists.openwall.com
Cc: robert.ancell at canonical.com
Subject: [oss-security] lightdm issues

Hi,

lightdm (0.9.2) which aims to be a xdm replacement seems to
fall into the same pitfalls like kdm and gdm recently. There is
a lot of uid 0 code creating and chown()ing files in user dirs such as
for ~/.dmrc and ~/.Xauthority. Probably more, depending on
how the permissions of cache and log directories are set up. For example
process_start() also creates and chown()s logfiles on users behalf.

There is also one thing that I dont understand about the lightdm
user itself and why pam sessions seem to be started for it inside
the greeter session code.

The xdmcp code seems to be OK so far, after a quick review.

---

Cheers,
        Moritz

-- System Information:
Debian Release: wheezy/sid
  APT prefers unstable
  APT policy: (500, ''unstable'')
Architecture: amd64 (x86_64)

Kernel: Linux 3.0.0-1-amd64 (SMP w/2 CPU cores)
Locale: LANG=de_DE.UTF-8, LC_CTYPE=de_DE.UTF-8 (charmap=UTF-8)
Shell: /bin/sh linked to /bin/dash