Kerberos vulnerability

National Cyber Alert System

Technical Cyber Security Alert TA04-247A


Vulnerabilities in MIT Kerberos 5

Original release date: September 3, 2004
Last revised: --
Source: US-CERT


Systems Affected

* MIT Kerberos 5 versions prior to krb5-1.3.5

* Applications that use versions of MIT Kerberos 5 libraries prior
to krb5-1.3.5

* Applications that contain code derived from MIT Kerberos 5

Updated vendor information is available in the systems affected
section of the individual vulnerability notes.


Overview

The MIT Kerberos 5 implementation contains several vulnerabilities,
the most severe of which could allow an unauthenticated, remote
attacker to execute arbitrary code on a Kerberos Distribution Center
(KDC). This could result in the compromise of an entire Kerberos
realm.


I. Description

There are several vulnerabilities in the MIT implementation of the
Kerberos 5 protocol. With one exception (VU#550464), all of the
vulnerabilities involve insecure deallocation of heap memory
(double-free vulnerabilities) during error handling and Abstract
Syntax Notation One (ASN.1) decoding. For further details, please see
the following vulnerability notes:

VU#795632 - MIT Kerberos 5 ASN.1 decoding functions insecurely
deallocate memory (double-free)

The MIT Kerberos 5 library does not securely deallocate heap memory
when decoding ASN.1 structures, resulting in double-free
vulnerabilities. An unauthenticated, remote attacker could execute
arbitrary code on a KDC server, which could compromise an entire
Kerberos realm. An attacker may also be able to execute arbitrary code
on Kerberos clients, or cause a denial of service on KDCs or clients.
(Other resources: MITKRB5-SA-2004-002, CAN-2004-0642)

VU#866472 - MIT Kerberos 5 ASN.1 decoding function krb5_rd_cred()
insecurely deallocates memory (double-free)

The krb5_rd_cred() function in the MIT Kerberos 5 library does not
securely deallocate heap memory when decoding ASN.1 structures,
resulting in a double-free vulnerability. A remote, authenticated
attacker could execute arbitrary code or cause a denial of service on
any system running an application that calls krb5_rd_cred(). This
includes Kerberos application servers and other applications that
process Kerberos authentication via the MIT Kerberos 5 library,
Generic Security Services Application Programming Interface (GSSAPI),
and other libraries.
(Other resources: MITKRB5-SA-2004-002, CAN-2004-0643)

VU#350792 - MIT Kerberos krb524d insecurely deallocates memory
(double-free)

The MIT Kerberos krb524d daemon does not securely deallocate heap
memory when handling an error condition, resulting in a double-free
vulnerability. An unauthenticated, remote attacker could execute
arbitrary code on a system running krb524d, which in many cases is
also a KDC. The compromise of a KDC system can lead to the compromise
of an entire Kerberos realm. An attacker may also be able to cause a
denial of service on a system running krb524d.
(Other resources: MITKRB5-SA-2004-002, CAN-2004-0772)

VU#550464 - MIT Kerberos 5 ASN.1 decoding function asn1buf_skiptail()
does not properly terminate loop

The asn1buf_skiptail() function in the MIT Kerberos 5 library does not
properly terminate a loop, allowing an unauthenticated, remote
attacker to cause a denial of service in a KDC, application server, or
Kerberos client.
(Other resources: MITKRB5-SA-2004-003, CAN-2004-0644)


II. Impact

The impacts of these vulnerabilities vary, but an attacker may be able
to execute arbitrary code on KDCs, systems running krb524d (typically
also KDCs), application servers, applications that use Kerberos
libraries directly or via GSSAPI, and Kerberos clients. An attacker
could also cause a denial of service on any of these systems.

The most severe vulnerabilities could allow an unauthenticated, remote
attacker to execute arbitrary code on a KDC system. This could result
in the compromise of both the KDC and an entire Kerberos realm.


III. Solution

Apply a patch or upgrade

Check with your vendor(s) for patches or updates. For information
about a specific vendor, please see the systems affected sections in
the individual vulnerability notes or contact your vendor directly.

Alternatively, apply the appropriate source code patch(es) referenced
in MITKRB5-SA-2004-002 and MITKRB5-SA-2004-003 and recompile.

These vulnerabilities will be addressed in krb5-1.3.5.


Appendix A. References

* Vulnerability Note VU#795632 -
<http://www.kb.cert.org/vuls/id/795632>

* Vulnerability Note VU#866472 -
<http://www.kb.cert.org/vuls/id/866472>

* Vulnerability Note VU#350792 -
<http://www.kb.cert.org/vuls/id/350792>

* Vulnerability Note VU#550464 -
<http://www.kb.cert.org/vuls/id/550464>

* MIT krb5 Security Advisory 2004-002 -
<http://web.mit.edu/kerberos/advisori...004-002-dblfre
e.txt>

* MIT krb5 Security Advisory 2004-003 -
<http://web.mit.edu/kerberos/www/advi...SA-2004-003-as
n1.txt>

* Kerberos: The Network Authentication Protocol -
<http://web.mit.edu/kerberos/www/>

__________________________________________________ _____________________

Thanks to Tom Yu and the MIT Kerberos Development team for addressing
these vulnerabilities and coordinating with vendors. MIT credits the
following people: Will Fiveash, Joseph Galbraith, John Hawkinson, Marc
Horowitz, and Nico Williams.
__________________________________________________ _____________________


Feedback can be directed to the author: Art Manion

__________________________________________________ _____________________

This document is available from:

<http://www.us-cert.gov/cas/techalerts/TA04-245A.html>