Software Engineering Institute

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.

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

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.