10700958 2003-09-16 21:44 +0200 /145 rader/ Dirk Mueller <mueller@kde.org>
Importerad: 2003-09-16 23:18 av Brevbäraren
Extern mottagare: kde-announce@kde.org
Mottagare: Bugtraq (import) <29034>
Ärende: [KDE SECURITY ADVISORY] KDM vulnerabilities
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From: Dirk Mueller <mueller@kde.org>
To: kde-announce@kde.org
Message-ID: <200309162144.32731.mueller@kde.org>
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KDE Security Advisory: KDM vulnerabilities
Original Release Date: 2003-09-16
URL: http://www.kde.org/info/security/advisory-20030916-1.txt
0. References
http://cert.uni-stuttgart.de/archive/suse/security/2002/12/
msg00101.html
http://cve.mitre.org/cgi-bin/cvename.cgi?name=CAN-2003-0690
http://cve.mitre.org/cgi-bin/cvename.cgi?name=CAN-2003-0692
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 credentials.
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 vulnerability.
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
running
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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(10700958) /Dirk Mueller <mueller@kde.org>/(Ombruten)