Multiple Vendor Kerberos kadmind Buffer Overflow Vulnerability

iDefense Security Advisory 04.03.07
http://labs.idefense.com/intelligence/vulnerabilities/
Apr 03, 2007

I. BACKGROUND

Kerberos is a network authentication protocol. It is used in
client-server systems to provide user authentication by using a ticket
based system. kadmind is the Kerberos administration server. It is used
to configure principals and policies on the Kerberos. More information
can be found on the vendor's website at the following URL.

http://web.mit.edu/Kerberos/

II. DESCRIPTION

Remote exploitation of a buffer overflow vulnerability in the Kerberos
kadmind server, as included in various vendors' operating system
distributions, could allow attackers to execute arbitrary code on a
targeted host.

The vulnerability exists within the server's logging function,
klog_vsyslog(). A call is made to vsprintf(), with the destination
buffer passed as a fixed size stack buffer. User input is not properly
validated before being passed to this function, and a stack based
buffer overflow can occur.

III. ANALYSIS

Exploitation allows an attacker to execute arbitrary code with root
privileges on the targeted host.

In order to exploit this vulnerability, an attacker must have valid
credentials stored on the server. Administrator privileges are not
necessary. The kadmind server runs on the master Kerberos server. Since
the master server holds the KDC principal and policy database, a
compromise could lead to a compromise of multiple hosts that use the
server for authentication.

IV. DETECTION

iDefense has confirmed the existence of this vulnerability with Kerberos
version 1.5.1 on Fedora CORE 5. It is likely that all distributions that
contain this version of Kerberos are vulnerable.

V. WORKAROUND

iDefense is currently unaware of any workarounds for this issue.

VI. VENDOR RESPONSE

The MIT Kerberos team has made patches available to address this
vulnerability. For more information consult their advisory at the
following URL.

http://web.mit.edu/Kerberos/advisories/MITKRB5-SA-2007-002-syslog.txt

VII. CVE INFORMATION

The Common Vulnerabilities and Exposures (CVE) project has assigned the
name CVE-2007-0957 to this issue. This is a candidate for inclusion in
the CVE list (http://cve.mitre.org/), which standardizes names for
security problems.

VIII. DISCLOSURE TIMELINE

02/08/2007  Initial vendor notification
02/08/2007  Initial vendor response
04/03/2007  Coordinated public disclosure

IX. CREDIT

The discoverer of this vulnerability wishes to remain anonymous.

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X. LEGAL NOTICES

Copyright © 2007 iDefense, Inc.

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Disclaimer: The information in the advisory is believed to be accurate
at the time of publishing based on currently available information. Use
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