[linux] [KDE SECURITY ADVISORY] KDM vulnerabilities (fwd)

Dave Dittrich dittrich at cac.washington.edu
Wed Sep 17 01:11:28 PDT 2003

I think the cookie vulnerability would affect systems that have X11/KDE
running and not ACL'd with iptables/ipchains. In general, you should
block 6000-6010 and just use OpenSSH (the new patched one!) with X11
tunneling enabled on a per-login basis (i.e., not enabled by default.)

Dave Dittrich Computing & Communications
dittrich at cac.washington.edu University Computing Services
http://staff.washington.edu/dittrich University of Washington

PGP key http://staff.washington.edu/dittrich/pgpkey.txt
Fingerprint FE97 0C57 0843 F3EB 49A1 0CD0 8E0C D0BE C838 CCB5

---------- Forwarded message ----------
Date: Tue, 16 Sep 2003 21:44:27 +0200
Subject: [KDE SECURITY ADVISORY] KDM vulnerabilities
From: Dirk Mueller <mueller at kde.org>
To: kde-announce at kde.org

KDE Security Advisory: KDM vulnerabilities
Original Release Date: 2003-09-16
URL: http://www.kde.org/info/security/advisory-20030916-1.txt

0. References

1. Systems affected:

All versions of KDM as distributed with KDE up to and including
KDE 3.1.3.

2. Overview:

Two issues have been discovered in KDM:

a) CAN-2003-0690:
Privilege escalation with specific PAM modules
b) CAN-2003-0692:
Session cookies generated by KDM are potentially insecure

KDM does not check for successful completion of the pam_setcred()
call. In case of error conditions in the installed PAM modules, KDM
might grant local root access to any user with valid login

It has been reported that a certain configuration of the MIT pam_krb5
module can result in a failing pam_setcred() call leaving the
session alive and providing root access to a regular user.

The Common Vulnerabilities and Exposures project (cve.mitre.org)
has assigned the name CAN-2003-0690 to this issue.

Additionally the session cookie generation algorithm used by KDM was
considered too weak to supply full 128 bits of entropy. This enables
non-authorized users to brute-force the session cookie.

The Common Vulnerabilities and Exposures project (cve.mitre.org)
has assigned the name CAN-2003-0692 to this issue.

3. Impact:

If KDM is used in combination with the MIT pam_krb5 module and given
a valid username and password of an existing user, the login attempt
succeeds and establishes a session with excessive privileges. This
may enable a local root compromise of the system.

It is possible that the same vulnerability exists if KDM is used
with other PAM modules. At the date of this advisory we are however
not aware of any other PAM module being affected by this

The weak cookie generation may allow non-authorized users to guess
the session cookie by a brute force attack, which allows, assuming
hostname / IP restrictions can be bypassed, to authorize to the
session and gain full access to it.

4. Solution:

a) Privilege escalation with specific PAM modules:

The patch listed in section 5 adds error checking to KDM and
aborts the login attempt if an error occurs during the
pam_setcred() call.

There is no intermediate workaround known. Users who do not use
PAM with KDM and users who use PAM with regular Unix crypt/MD5 based
authentication are not affected.

b) Weak cookie generation:

The patch listed in section 5 adds a new cookie generation algorithm,
which uses /dev/urandom as non-predictable source of entropy.

Users of KDE 2.2.2 are advised to upgrade to KDE 3.1.4. A patch for
KDE 2.2.2 is available for users who are unable to upgrade to
KDE 3.1.

Users of KDE 3.0.x are advised to upgrade to KDE 3.1.4. A patch for
KDE 3.0.5b is available for users who are unable to upgrade to
KDE 3.1.

Users of KDE 3.1.x are advised to upgrade to KDE 3.1.4.

5. Patch:

A patch for KDE 2.2.2 is available from
ftp://ftp.kde.org/pub/kde/security_patches :

4672868343b26e0c0eae91fffeff1f7e post-2.2.2-kdebase-kdm.patch

A patch for KDE 3.0.5b is available from
ftp://ftp.kde.org/pub/kde/security_patches :

fde237203fc7b325c34d2f90a463db3f post-3.0.5-kdebase-kdm.patch

A patch for KDE 3.1.3 is available from
ftp://ftp.kde.org/pub/kde/security_patches :

8553c20798b321e333d8c516636f2297 post-3.1.3-kdebase-kdm.patch

6. Time line and credits:

12/06/2002 Posting on suse-security mailing list describing the
PAM vulnerability.
08/06/2003 Notification of KDE Security and the KDM maintainer
about the PAM vulnerability by Stephan Kulow.
08/09/2003 Patches for the PAM vulnerability applied to KDE CVS.
08/20/2003 George Lebl notifies Oswald Buddenhagen about weak
session cookie generation in KDM.
08/26/2003 Impact analysis and advisory finished.
09/04/2003 Patches for the weak cookie vulnerability applied to CVS.
09/16/2003 Public advisory.

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