Cisco Security Advisory

Contents

Summary
Affected Products
Details
Vulnerability Scoring Details
Impact
Software Versions and Fixes
Workarounds
Obtaining Fixed Software
Exploitation and Public Announcements
Status of This Notice: Final
Distribution
Revision History
Cisco Security Procedures

Vulnerable Products

Products Confirmed Not Vulnerable

The RTR feature allows you to monitor network performance, network resources, and applications by measuring response times and availability. With this feature you can perform troubleshooting, problem notifications, and problem analysis based on response time reporter statistics.

A router is vulnerable only if the RTR responder is enabled. In order to verify this, check the router's configuration. Execute the following command while logged on a router:

Router>show rtr responder
     RTR Responder is: Enabled
     Number of control messages received: 0 Number of errors: 0 
     Recent sources:
     Recent error sources:

If you notice the line "RTR Responder is: Enabled," then you are vulnerable.

Alternatively, you can use this procedure:

Router>show ip socket
     show ip socket
     Proto    Remote      Port      Local       Port  In Out Stat TTY OutputIF
     ....
      17 0.0.0.0             0 10.0.0.1         1967   0   0   89   0

If you notice a line as in the example above where the router is listening to the port 1967, then you are vulnerable.

For Cisco IOS Software, this vulnerability is documented as two Cisco Bug IDs: CSCdx17916 and CSCdx61997.

Cisco has not provided scores for the vulnerabilities in this advisory based on the Common Vulnerability Scoring System (CVSS). At the time of original publication, CVSS scoring in Cisco Security publications had not been adopted.

CVSS is a standards-based scoring method that conveys vulnerability severity and helps determine urgency and priority of response.

Cisco has provided a base and temporal score. Customers can then compute environmental scores to assist in determining the impact of the vulnerability in individual networks. 

Cisco has provided an FAQ to answer additional questions regarding CVSS at
http://www.cisco.com/web/about/security/intelligence/cvss-qandas.html .

Cisco has also provided a CVSS calculator to help compute the environmental impact for individual networks at
http://intellishield.cisco.com/security/alertmanager/cvss .

Each row of the Cisco IOS software table (below) describes a release train and the platforms or products for which it is intended. If a given release train is vulnerable, then the earliest possible releases that contain the fix (the "First Fixed Release") and the anticipated date of availability for each are listed in the "Rebuild," "Interim," and "Maintenance" columns. A device running a release in the given train that is earlier than the release in a specific column (less than the First Fixed Release) is known to be vulnerable. The release should be upgraded at least to the indicated release or a later version (greater than or equal to the First Fixed Release label). When selecting a release, keep in mind the following definitions.

• Maintenance - The most heavily tested, stable, and highly recommended release of a release train in any given row of the table.
• Rebuild - Constructed from the previous maintenance or major release in the same train, it contains the fix for a specific defect. Although it receives less testing, it contains only the minimal changes necessary to repair the vulnerability.
• Interim - Built at regular intervals between maintenance releases and receives less testing. Interims should be selected only if there is no other suitable release that addresses the vulnerability. Interim images should be upgraded to the next available maintenance release as soon as possible. Interim releases are not available through manufacturing, and usually they are not available for customer download from http://www.cisco.com without prior arrangement with the Cisco TAC.

In all cases, customers should exercise caution to confirm that the devices to be upgraded contain sufficient memory and that current hardware and software configurations will continue to be supported properly by the new software release. If the information is not clear, contact the Cisco TAC for assistance as shown in the Obtaining Fixed Software section below.

More information on Cisco IOS software release names and abbreviations is available at http://www.cisco.com/web/about/security/intelligence/ios-ref.html.

The fixes will be available at the Software Center located at http://www.cisco.com/tacpage/sw-center/.

There is no workaround short of disabling the RTR responder. It is possible to mitigate the vulnerability by applying the ACL on the router.

If you want to disable the RTR, you need to execute the following commands:

Router#conf t
     Enter configuration commands, one per line.  End with CNTL/Z.
     Router(config)#no rtr responder
     Router(config)#exit
     Router#copy running-config startup-config

If you want to block all offending packets on your network edge, then you should create an ACL, or modify an existing one, to contain an entry resembling:

Router#conf t
     Enter configuration commands, one per line.  End with CNTL/Z.
     Router(config)#access-list 101 deny udp any any eq 1967
     Router(config)#interface eth0
     Router(config)#ip access-group 101 in

In this example the interface eth0 is assumed to be facing toward the network edge. You will have to substitute it for the correct interface on your router.

This will prevent any packet that is destined to the port 1967/UDP from entering your network. If you need to enable these packets to traverse your network, then the ACL must exclude only your internal routers.

In addition to filtering packets at the network edge, you may apply filtering on the device itself and permit packets only from known good sources. This will contribute to the overall mitigation of this issue.

Router#conf t
     Enter configuration commands, one per line.  End with CNTL/Z.
     Router(config)#access-list 101 permit udp 10.0.0.1 10.0.0.10 eq 1967
     Router(config)#access-list 101 deny udp any 10.0.0.10 eq 1967
     Router(config)#interface eth0
     Router(config-if)#ip access-group 101 in

In this example, 10.0.0.1 is the legitimate source and 10.0.0.10 is the address of the router itself.

Customers with Service Contracts

Customers Using Third-Party Support Organizations

Customers Without Service Contracts

THIS DOCUMENT IS PROVIDED ON AN "AS IS" BASIS AND DOES NOT IMPLY ANY KIND OF GUARANTEE OR WARRANTY, INCLUDING THE WARRANTIES OF MERCHANTABILITY OR FITNESS FOR A PARTICULAR USE. YOUR USE OF THE INFORMATION ON THE DOCUMENT OR MATERIALS LINKED FROM THE DOCUMENT IS AT YOUR OWN RISK. CISCO RESERVES THE RIGHT TO CHANGE OR UPDATE THIS DOCUMENT AT ANY TIME.

A stand-alone copy or Paraphrase of the text of this document that omits the distribution URL in the following section is an uncontrolled copy, and may lack important information or contain factual errors.

This advisory will be posted on Cisco's worldwide website at http://tools.cisco.com/security/center/content/CiscoSecurityAdvisory/cisco-sa-20030515-saa

In addition to worldwide web posting, a text version of this notice is clear-signed with the Cisco PSIRT PGP key and is posted to the following e-mail and Usenet news recipients.

• cust-security-announce@cisco.com
• bugtraq@securityfocus.com
• full-disclosure@lists.netsys.com
• first-teams@first.org (includes CERT/CC)
• cisco@spot.colorado.edu
• cisco-nsp@puck.nether.net
• comp.dcom.sys.cisco
• Various internal Cisco mailing lists

Future updates of this advisory, if any, will be placed on Cisco's worldwide website, but may or may not be actively announced on mailing lists or newsgroups. Users concerned about this problem are encouraged to check the above URL for any updates.

Complete information on reporting security vulnerabilities in Cisco products, obtaining assistance with security incidents, and registering to receive security information from Cisco, is available on Cisco's worldwide website at http://www.cisco.com/en/US/products/products_security_vulnerability_policy.html. This includes instructions for press inquiries regarding Cisco security notices. All Cisco security advisories are available at http://www.cisco.com/go/psirt.