Multiple Cisco products contain vulnerabilities in the processing of H.323 messages, which are typically used in Voice over Internet Protocol (VoIP) or multimedia applications. A test suite has been developed by the University of Oulu to target this protocol and identify vulnerabilities. Support for the H.323 protocol was introduced in Cisco IOS® Software Release 11.3T. Release 11.3T, and all later Cisco IOS releases may be affected if the software includes support for voice/multimedia applications. Vulnerable devices include those that contain software support for H.323 as network elements as well as those configured for IOS Network Address Translation (NAT) and those configured for IOS Firewall (also known as Context-Based Access Control [CBAC]). Other Cisco voice products that do not run Cisco IOS may also be affected. These vulnerabilities can be exploited repeatedly to produce a denial of service (DoS). This advisory is available at https://sec.cloudapps.cisco.com/security/center/content/CiscoSecurityAdvisory/cisco-sa-20040113-h323.