Products & Services

This section provides details on affected products.

Vulnerable Products

Products Confirmed Not Vulnerable

Cisco IOS Firewall is a packet inspection system. It is also a stateful system; it keeps information about connections that last beyond the lifetime of a single packet. CBAC is an IP-only feature. A router running CBAC recognizes Transmission Control Protocol (TCP), User Datagram Protocol (UDP), and some higher-layer protocols, and examines packet data beyond the IP headers. If configured, CBAC maintains session information based on packets examined.

When a session is initiated from the protected network, CBAC creates a dynamic access list entry allowing return traffic for that session. Upon inspection of the return traffic through a dynamic access list, source and destination addresses and ports are checked, however IP protocol type is not checked. This could allow a packet of different protocol type into the protected network.

This vulnerability is documented as Cisco Bug ID CSCdv48261.

By allowing packets of different type into the protected network, the customer is exposed to much bigger threat. This vulnerability can be exploited for reconnaissance purposes, but only for a single port and host that initiated a session in the first place. Depending on the exact session parameters, it may be possible to send data to processes that were supposed to be accessible only from within the trusted network. In the worst case, it is possible to open an interactive session to a host on the protected network. In that case, there must be a process running on the host that is listening to the port for which a hole is opened by CBAC.

Each row of the table 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 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 earliest fixed release) is known to be vulnerable. The release should be upgraded at least to the indicated release or a later version (greater than the earliest fixed release label). When selecting a release, keep in mind the following definitions:

• Maintenance - Most heavily tested and highly recommended release of any label in a 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 effect the repair.
  
• 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 via manufacturing, and usually they are not available for customer download from CCO without prior arrangement with the Cisco TAC.
  

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

More information on Cisco IOS release names and abbreviations is available at http://www.cisco.com/warp/public/620/1.html.

There is no workaround.

Cisco has made free software available to address this vulnerability for affected customers. Prior to deploying software, customers should consult their maintenance provider or check the software for feature set compatibility and known issues specific to their environment.

Customers may only install and expect support for the feature sets they have purchased. By installing, downloading, accessing or otherwise using such software upgrades, customers agree to be bound by the terms of Cisco's software license terms found at http://www.cisco.com/public/sw-license-agreement.html, or as otherwise set forth at Cisco.com Downloads at http://www.cisco.com/public/sw-center/sw-usingswc.shtml.

Do not contact either "psirt@cisco.com" or "security-alert@cisco.com" for software upgrades.

This vulnerability was discovered by a customer. The Cisco PSIRT is not aware of any public announcements or malicious use of the vulnerabilities described in this advisory.

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 notice will be posted on Cisco's Worldwide Web site at http://tools.cisco.com/security/center/content/CiscoSecurityAdvisory/cisco-sa-20011128-ios-cbac-dynacl. 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
  
• first-teams@first.org (includes CERT/CC)
  
• cisco@spot.colorado.edu
  
• comp.dcom.sys.cisco
  
• firewalls@lists.gnac.com
  
• 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.