Cisco IOS 11.1(x) through 11.3(x) and 12.0(x) through 12.2(x), when configured for BGP routing, allows remote attackers to cause a denial of service (device reload) via malformed BGP (1) OPEN or (2) UPDATE messages.

**Overview**

Multiple implementations of the Border Gateway Protocol (BGP) contain vulnerabilities related to the processing of UPDATE and OPEN messages. The impacts of these vulnerabilities appear to be limited to denial of service.

**Description**

BGP (RFC 1771) is designed to exchange network reachability information between peer nodes. Information advertised by a BGP system to its peers includes timers, metrics, and paths to different Autonomous System (AS) networks. Routing between AS networks depends on BGP, and the Internet is a network of AS networks. Therefore, vulnerabilities in BGP have the potential to affect the Internet infrastructure.

Multiple BGP implementations contain vulnerabilities handling exceptional OPEN and UPDATE messages. While the details of the individual vulnerabilities are different, the impacts appear to be limited to denial of service. In addition, most BGP implementations do not accept messages from arbitrary sources. Some BGP implementations only accept TCP connections (179/tcp) from properly configured peers, and some implementations require a valid AS number in the BGP message data. To deliver malicious messages to such systems, an attacker would need to spoof a TCP connection or have access to a trusted BGP peer. The attacker may also need to know a valid AS number.

For information about specific BGP implementations, please see the Systems Affected section below.

**Impact**

A remote attacker can cause a denial of service in a vulnerable system. In most cases, the attacker would need to act as a valid BGP peer. BGP session instability can result in "flapping" and other routing problems that may adversely affect Internet traffic.

**Solution**

**Apply a patch or upgrade**  
Apply a patch or upgrade as specified by your vendor.

**Restrict BGP access**

Using access control lists (ACLs) and BGP configuration settings, restrict access to valid networks and BGP peers.

**Authenticate BGP messages**

TCP MD5 (RFC 2385), IPsec, and S-BGP provide cryptographic authentication of network connections and/or BGP messages. Various performance and key distribution issues are associated with these authentication methods.

**Use out-of-band management channels**

When possible, use an out-of-band channel, such as a separate network, to transmit BGP other management traffic.

**Vendor Information**

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**References****Acknowledgements**

These vulnerabilities were reported as a result of research done by Cisco. Thanks to Cisco for sharing this research and helping to coordinate the disclosure of information about these vulnerabilities.

This document was written by Art Manion.

**Other Information**

**CVE IDs:**

CVE-2004-0589

**Severity Metric:**

8.60

**Date Public:**

2004-06-16

**Date First Published:**

2004-06-16

**Date Last Updated:**

2004-06-28 16:09 UTC

**Document Revision:**

39

CVE-2004-0589: CERT/CC Vulnerability Note VU#784540

Denial of service in Cisco routers running NAT via a PORT command from an FTP client to a Telnet port.

CVE-1999-0843: IBM X-Force Exchange

Cisco Gigabit Switch routers running IOS allow remote attackers to forward unauthorized packets due to improper handling of the "established" keyword in an access list.

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