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January 2008

3555 - Cisco Security Advisory: Cisco PIX and ASA Time-to-Live Vulnerability

ID: 3555
Date: 24/01/2008

Title: 3555 - Cisco Security Advisory: Cisco PIX and ASA Time-to-Live Vulnerability
Platform level affected:Security Software
Specific operating systems components affected: Other
Security software:Firewall
Remediation Summary:Update your copy of the software with the download available from the supplier.
Vendors affected:Cisco
Applications affected:PIX 500 Series Security Appliance (PIX) and the Cisco 5500 Series Adaptive Security Appliance (ASA)
Adversity source: Unknown
Attack Vector: Vulnerability exploitation
Virulence: Unknown
Warning Status: Unknown
Potential Damage: Network DOS
Possible Duration: Unknown
Availability of fix: Available
Type of fix: Patch
Source: Cisco
Source URL: http://www.cisco.com/warp/public/707/cisco-sa-20080123-asa.shtml
Abstract: A crafted IP packet vulnerability exists in the Cisco PIX 500 Series Security Appliance (PIX) and the Cisco 5500 Series Adaptive Security Appliance (ASA) that may result in a reload of the device.

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Cisco Security Advisory: Cisco PIX and ASA Time-to-Live Vulnerability

Advisory ID: cisco-sa-20080123-asa

http://www.cisco.com/warp/public/707/cisco-sa-20080123-asa.shtml

Revision 1.0

For Public Release 2008 January 23 1600 UTC (GMT)

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Summary
=======

A crafted IP packet vulnerability exists in the Cisco PIX 500 Series Security Appliance (PIX) and the Cisco 5500 Series Adaptive Security Appliance (ASA) that may result in a reload of the device. This vulnerability is triggered during processing of a crafted IP packet when the Time-to-Live (TTL) decrement feature is enabled.

Common Vulnerabilities and Exposures (CVE) identifier CVE-2008-0028 has been assigned to this vulnerability.

Cisco has released free software updates that address this vulnerability. A workaround that mitigates this vulnerability is available.

This advisory is posted at
http://www.cisco.com/warp/public/707/cisco-sa-20080123-asa.shtml.

Affected Products
=================

Vulnerable Products
+------------------

The TTL decrement feature was introduced in version 7.2(2) and it is disabled by default. The Cisco PIX and ASA security appliances running software versions prior to 7.2(3)006 or 8.0(3) and that have the TTL decrement feature enabled are vulnerable.

By default the PIX and ASA security appliance software does not decrement the TTL of transient packets. The ability to decrement the TTL of transient packets can be enabled on a selective or global basis by using the set connection decrement-ttl command in the policy-map class configuration mode. To determine whether you are running this feature use the show running-config command and search for the set connection decrement-ttl command. Alternatively you can use the include argument to search for this command as follows:

    ASA#show running-config | include decrement-ttl
    set connection decrement-ttl
    ASA#

The set connection decrement-ttl command is part of a configured class-map. In order for this command to take effect it must be applied using a policy-map (assigned globally or to an interface). For more information about the Modular Policy Framework on the Cisco ASA and PIX refer to the following link:

http://www.cisco.com/en/US/docs/security/asa/asa80/configuration/guide/mpc.html

To determine whether you are running a vulnerable version of Cisco PIX or ASA software, issue the show version command-line interface (CLI) command. The following example shows a Cisco ASA Security Appliance that runs software release 7.2(3):

ASA#show version

Cisco Adaptive Security Appliance Software Version 7.2(3)

[...]

Customers who use the Cisco Adaptive Security Device Manager (ASDM) to manage their devices can find the version of the software displayed in the table in the login window or in the upper left corner of the ASDM window. The version notation is similar to the following:

PIX Version 7.2(3)

Products Confirmed Not Vulnerable
+--------------------------------

Cisco PIX and ASA security appliances which do not support the TTL decrement feature or are not explicitly configured for it are not vulnerable.

Note: The TTL decrement feature was introduced in version 7.2(2), and it is disabled by default. The Cisco Firewall Services Module (FWSM) is not vulnerable.

No other Cisco products are currently known to be affected by this vulnerability.

Details
=======

Vulnerability Scoring Details
+----------------------------

Cisco has provided scores for the vulnerability in this advisory based on the Common Vulnerability Scoring System (CVSS). The CVSS scoring in this Security Advisory is done in accordance with CVSS version 2.0.

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.

* Cisco PIX and ASA TTL Vulnerability (CSCsk48199)

CVSS Base Score - 7.8
    Access Vector -            Network
    Access Complexity -        Low
    Authentication -           None
    Confidentiality Impact -   None
    Integrity Impact -         None
    Availability Impact -      Complete

CVSS Temporal Score - 6.4
    Exploitability -           Functional
    Remediation Level -        Official-Fix
    Report Confidence -        Confirmed

Impact
======

Successful exploitation of the vulnerability described in this advisory will result in a reload of the affected device. Repeated exploitation can result in a sustained denial of service (DoS) condition.

Software Versions and Fixes
===========================

This vulnerability is fixed in software version 7.2(3)6 or 8.0(3) and later.

When considering software upgrades, also consult http://www.cisco.com/go/psirt and any subsequent advisories to determine exposure and a complete upgrade solution.

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 Technical Assistance Center (TAC) or your contracted maintenance provider for assistance.

Workarounds
===========

Disable the TTL decrement feature using the no set connection decrement-ttl command in class configuration mode.

    ASA(config)#policy-map localpolicy1
    ASA(config-pmap)#class local_server
    ASA(config-pmap-c)#no set connection decrement-ttl
    ASA(config-pmap-c)#exit

For additional information on identifying and mitigating TTL based attacks, please refer to the Cisco Applied Intelligence White Paper "TTL Expiry Attack Identification and Mitigation", available at:

http://cisco.com/web/about/security/intelligence/ttl-expiry.html

Obtaining Fixed Software
========================

Cisco has released free software updates that address this vulnerability. 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/en/US/products/prod_warranties_item09186a008088e31f.html,
or as otherwise set forth at Cisco.com Downloads at http://www.cisco.com/public/sw-center/sw-usingswc.shtml.

Do not contact 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/warp/public/687/Directory/DirTAC.shtml
for additional TAC contact information, including localized telephone numbers, and instructions and e-mail addresses for use in various languages.

Exploitation and Public Announcements
=====================================

The Cisco PSIRT is not aware of any public announcements or malicious use of the vulnerability described in this advisory.

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://www.cisco.com/warp/public/707/cisco-sa-20080123-asa.shtml

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
================

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/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.

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All contents are Copyright (C) 2006-2008 Cisco Systems, Inc. All rights reserved.
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Updated: Jan 21, 2008 Document ID: 100314

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This advisory contains information released by the original author. Some of the information may have changed since it was released. If the issue affects you, it may be prudent to retrieve the advisory from the site of the original source to ensure that you receive the most current information concerning that problem. Reference to any specific commercial product, process, or service by trade name, trademark manufacturer, or otherwise, does not constitute or imply its endorsement, recommendation, or favouring by CPNI.

The views and opinions of authors expressed within this notice shall not be used for advertising or product endorsement purposes. CPNI shall not accept responsibility for any errors or omissions contained within this advisory. In particular, they shall not be liable for any loss or damage whatsoever, arising from or in connection with the usage of information contained within this advisory.

CSIRTUK is a member of the Forum of Incident Response and Security Teams (FIRST) and has contacts with other international Incident Response Teams (IRTs) in order to foster cooperation and coordination in incident prevention, to prompt rapid reaction to incidents, and to promote information sharing amongst its members and the community at large.