Vulnerability Note VU#587579

MIT Kerberos V5 ASN.1 decoder fails to perform bounds checking on data element length fields

Overview

The MIT Kerberos V5 implementation contains an ASN.1 decoding flaw that may allow remote attackers to crash affected Kerberos applications.

I. Description

Kerberos V5 protocol messages are defined using Abstract Syntax Notation One (ASN.1), a formal language that allows protocol specifications to be easily encoded for network transmission. For example, each data element in a given protocol message is encoded with additional information that indicates the type and length of the supplied data. This standardized format allows the recipient of the message to interpret the data elements and handle them appropriately.

The ASN.1 decoder included with MIT Kerberos V5 fails to perform bounds checking on the length values supplied with each data element. In some cases, an incoming message can contain a large unsigned data element length value that is misinterpreted as a negative signed value. When an affected Key Distribution Center (KDC) or other Kerberos application attempts to allocate negative or unreasonably large amounts of storage, an error condition will occur that may cause the application to crash.

II. Impact

This vulnerability allows remote attackers to crash affected applications, resulting in a denial of service condition.

III. Solution

This vulnerability was addressed in MIT Kerberos V5 1.2.5, released on April 30, 2002. MIT krb5 Security Advisory 2003-001 provides additional information from MIT and is available at:

http://web.mit.edu/kerberos/www/advisories/MITKRB5-SA-2003-001-multiple.txt

For information regarding other vendors who may be affected, please see the vendor section of this document.

Systems Affected

Vendor	Status	Date Updated
Apple Computer Inc.	Unknown	29-Jan-2003
BSDI	Unknown	29-Jan-2003
Cisco Systems Inc.	Unknown	29-Jan-2003
Conectiva	Unknown	29-Jan-2003
Cray Inc.	Unknown	31-Jan-2003
Debian	Unknown	29-Jan-2003
Hewlett-Packard Company	Not Vulnerable	31-Jan-2003
IBM	Unknown	31-Jan-2003
KTH Kerberos	Unknown	29-Jan-2003
MandrakeSoft	Vulnerable	4-Apr-2003
Microsoft Corporation	Not Vulnerable	31-Jan-2003
MIT Kerberos Development Team	Vulnerable	30-Jan-2003
NetBSD	Unknown	29-Jan-2003
OpenBSD	Unknown	29-Jan-2003
Red Hat Inc.	Vulnerable	27-Mar-2003
Sun Microsystems Inc.	Unknown	29-Jan-2003
The SCO Group	Unknown	29-Jan-2003
Wind River Systems Inc.	Unknown	29-Jan-2003

References

http://web.mit.edu/kerberos/www/advisories/MITKRB5-SA-2003-001-multiple.txt
http://www.ietf.org/rfc/rfc1510.txt

Credit

The reporter of this vulnerability wishes to remain anonymous.

This document was written by Jeffrey P. Lanza.

Other Information

Date Public	01/28/2003
Date First Published	01/31/2003 02:02:44 PM
Date Last Updated	04/04/2003
CERT Advisory
CVE Name	CAN-2002-0036
US-CERT Technical Alerts
Metric	31.50
Document Revision	43

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