Vulnerability Note VU#350792

MIT Kerberos krb524d insecurely deallocates memory (double-free)

Overview

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 Kerberos Distribution Center (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.

I. Description

As described on the MIT Kerberos web site: "Kerberos is a network authentication protocol. It is designed to provide strong authentication for client/server applications by using secret-key cryptography." MIT Kerberos code is used in network applications from a variety of different vendors and is included in many UNIX and Linux distributions.

The MIT Kerberos krb524d daemon converts Kerberos 5 service tickets into Kerberos 4 service tickets. There is a double-free vulnerability in krb524d that can be triggered during the conversion of a cross-realm ticket. From MITKRB5-SA-2004-002:

The patch (introduced in krb5-1.2.8 and present in all subsequent

releases) for disabling krb4 cross-realm authentication in krb524d

introduced a double-free vulnerability. If handle_classic_v4() denies

the conversion of a cross-realm ticket, v5tkt->enc_part2 gets freed

but not nulled, so do_connection() double-frees many things when it

subsequently calls krb5_free_ticket().

II. Impact

An unauthenticated, remote attacker to could execute arbitrary code on a system running krb524d. In many cases, this system also operates a KDC, so this vulnerability could allow an attacker to gain the master secret for a Kerberos realm, leading to compromise of the entire realm. An attacker may also be able to crash a system running krb524d, causing a denial of service.

III. Solution

Apply a patch

Apply the appropriate patch(es) referenced in MITKRB5-SA-2004-002 or specified by your vendor.

Upgrade

According to MITKRB5-SA-2004-002, "The upcoming krb5-1.3.5 release will contain fixes for these problems."

Restrict access

Depending on network architecture, it may be practical to restrict access to systems running krb524d (4444/udp) from untrusted networks such as the Internet. While this will help to limit the source of attacks, it will not prevent attacks from trusted hosts or networks or attackers who can successfully spoof their source addresses.

Systems Affected

Vendor	Status	Date Updated
Cisco Systems Inc.	Not Vulnerable	3-Sep-2004
CyberSafe	Not Vulnerable	2-Sep-2004
MIT Kerberos Development Team	Vulnerable	2-Sep-2004

References

http://web.mit.edu/kerberos/advisories/MITKRB5-SA-2004-002-dblfree.txt
http://web.mit.edu/kerberos/www/
http://www.cmf.nrl.navy.mil/CCS/people/kenh/kerberos-faq.html#krb524d
http://www.cmf.nrl.navy.mil/CCS/people/kenh/kerberos-faq.html#kerbfirewall
http://www.securitytracker.com/alerts/2004/Aug/1011106.html

Credit

Thanks to Tom Yu and the MIT Kerberos Development Team for reporting this vulnerability and coordinating with vendors. MITKRB5-SA-2004-002 acknowledges Marc Horowitz.

This document was written by Art Manion.

Other Information

Date Public	08/31/2004
Date First Published	09/02/2004 01:12:56 PM
Date Last Updated	09/03/2004
CERT Advisory
CVE-ID(s)	CAN-2004-0772
NVD-ID(s)	CAN-2004-0772
US-CERT Technical Alerts
Metric	10.28
Document Revision	16

If you have feedback, comments, or additional information about this vulnerability, please send us email.

Get Adobe Reader