Cisco Security Advisory

Cisco Secure PIX Firewall TCP Reset Vulnerability

Advisory ID: cisco-sa-20000711-pix-tcp-reset

http://tools.cisco.com/security/center/content/CiscoSecurityAdvisory/cisco-sa-20000711-pix-tcp-reset

Revision 1.0

For Public Release 2000 July 11 10:00  UTC (GMT)


Summary

The Cisco Secure PIX Firewall cannot distinguish between a forged TCP Reset (RST) packet and a genuine TCP RST packet. Any TCP/IP connection established through the Cisco Secure PIX Firewall can be terminated by a third party from the untrusted network if the connection can be uniquely determined. This vulnerability is independent of configuration. There is no workaround.

This vulnerability exists in all Cisco Secure PIX Firewall software releases up to and including 4.2(5), 4.4(4), 5.0(3) and 5.1(1). The defect has been assigned Cisco bug ID CSCdr11711.

This advisory is posted at http://tools.cisco.com/security/center/content/CiscoSecurityAdvisory/cisco-sa-20000711-pix-tcp-reset.

Affected Products

This section provides details on affected products.

Vulnerable Products

Cisco Secure PIX Firewalls with software versions up to and including 4.2(5), 4.4(4), 5.0(3) and 5.1(1) are affected.

Products Confirmed Not Vulnerable

No other Cisco products are currently known to be affected by these vulnerabilities.

Details

When the Cisco Secure PIX Firewall receives a TCP Reset (RST) packet, it evaluates that packet based on data contained in the TCP packet header: source IP address, source port, destination IP address, and destination port. If these four values match an entry in the stateful inspection table, the associated connection will be reset. This affects only TCP sessions. Data exchange based on any other protocol is not affected.

To exploit this vulnerability, an attacker would need to have or infer:

  • Detailed knowledge of the connection table in the Cisco Secure PIX Firewall prior to launching the attack, or
  • Detailed knowledge of the source and destination IP Address and ports associated with a particular connection to be attacked

This particular vulnerability only affects the connection table (which keeps state regarding the connections being made through the device). It does not affect the translation table (in which address mappings are stored).

Cisco Secure PIX Firewall software has been fixed so that it now checks for a valid sequence number before removing a connection from the connection state table.

Vulnerability Scoring Details

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 was not yet adopted.

Impact

Any Cisco Secure PIX Firewall that provides external access to the Internet and for which all of the preceding conditions are met is vulnerable to the disruption of individual sessions.

Software Versions and Fixes

For the version listed in the left-most column below, customers should upgrade to at least the version shown in the center column. Please note the hardware requirements following the table.

Affected Version

Projected First Fixed Regular Release *

Date Available

All versions of Cisco Secure PIX up to version 4.2(5), including 2.7, 3.0, 3.1, 4.0, 4.1

4.4(5)

2000-06-09

All 4.3x and 4.4x versions up to and including version 4.4(4)

4.4(5)

2000-06-09

Version 5.0.x up to and including version 5.0(3)

5.1(2)

2000-06-09

Version 5.1.1

5.1(2)

2000-06-09

* Fix will carry forward into all later versions

A 128MB upgrade for the PIX Firewall is necessary if:

  • Version 4.3 or 4.4 is used on a PIX 'Classic' (excluding PIX10000, PIX-510, PIX-520, and PIX-515)
  • Version 5.0 is used on a PIX 'Classic', PIX10000, or PIX-510 (excluding PIX-520 and PIX-515)

As with any new software installation, customers planning to upgrade should carefully read the release notes and other relevant documentation before beginning any upgrade. Also, it is important to be certain that the new version of Cisco Secure PIX Firewall software is supported by your hardware and especially that enough memory is available.


Workarounds

There are no workarounds for this defect. Customers are urged to upgrade to the versions of code containing the fix for CSCdr11711.

Obtaining Fixed Software

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.

Customers with Service Contracts

Customers with contracts should obtain upgraded software through their regular update channels. For most customers, this means that upgrades should be obtained through the Software Center on Cisco's worldwide website at http://www.cisco.com.

Customers Using Third-Party Support Organizations

Customers whose Cisco products are provided or maintained through prior or existing agreements with third-party support organizations, such as Cisco Partners, authorized resellers, or service providers should contact that support organization for guidance and assistance with the appropriate course of action in regards to this advisory.

The effectiveness of any workaround or fix is dependent on specific customer situations, such as product mix, network topology, traffic behavior, and organizational mission. Due to the variety of affected products and releases, customers should consult with their service provider or support organization to ensure any applied workaround or fix is the most appropriate for use in the intended network before it is deployed.

Customers Without Service Contracts

Customers who purchase direct from Cisco but do not hold a Cisco service contract, and customers who purchase through third-party vendors but are unsuccessful in obtaining fixed software through their point of sale should acquire upgrades by contacting the Cisco Technical Assistance Center (TAC). TAC contacts are as follows.

  • +1 800 553 2447 (toll free from within North America)
  • +1 408 526 7209 (toll call from anywhere in the world)
  • e-mail: tac@cisco.com

Customers should have their product serial number available and be prepared to give the URL of this notice as evidence of entitlement to a free upgrade. Free upgrades for non-contract customers must be requested through the TAC.

Refer to http://www.cisco.com/en/US/support/tsd_cisco_worldwide_contacts.html for additional TAC contact information, including localized telephone numbers, and instructions and e-mail addresses for use in various languages.

Exploitation and Public Announcements

Cisco has received no reports of malicious exploitation of this vulnerability. The vulnerability was reported to Cisco by a customer and has been discussed on BUGTRAQ, a public full-disclosure security mailing list.

Status of This Notice: Final

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.


Distribution

This advisory is posted on Cisco's worldwide website at:

http://tools.cisco.com/security/center/content/CiscoSecurityAdvisory/cisco-sa-20000711-pix-tcp-reset

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
  • first-teams@first.org
  • bugtraq@securityfocus.com
  • vulnwatch@vulnwatch.org
  • cisco@spot.colorado.edu
  • cisco-nsp@puck.nether.net
  • full-disclosure@lists.grok.org.uk
  • comp.dcom.sys.cisco@newsgate.cisco.com

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.


Revision History

Revision 1.0

2000-July -11

Initial public release.

Cisco Security Procedures

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/web/about/security/psirt/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.


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