[nsp] Cisco Security Advisory: A Vulnerability in IOS Firewall Feature Set

From: Cisco Systems Product Security Incident Response Team (psirt@cisco.com)
Date: Wed Nov 28 2001 - 11:10:23 EST

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Cisco Security Advisory: A Vulnerability in IOS Firewall Feature Set

Revision 1.0

For Public Release 2001 November 28 08:00 (UTC -0800)

Summary

   The IOS Firewall Feature set, also known as Cisco Secure Integrated
   Software, also known as Context Based Access Control, and introduced
   in IOS version 11.2P, has a vulnerability which permits traffic
   normally expected to be denied by the dynamic access control lists.

   This vulnerability is documented as Cisco Bug ID CSCdv48261.

   No other Cisco product is vulnerable.

   There is no workaround.

   This advisory is available at the
   http://www.cisco.com/warp/public/707/IOS-cbac-dynacl-pub.shtml

Affected Products

   Only configurations implementing CBAC are affected. An affected
   configuration includes the lines "ip inspect" in your router's
   configuration. Here is one example:

ip inspect name rule1 udp
ip inspect name rule1 tcp
!
!
interface FastEthernet0/1
ip address 1.2.3.4 255.255.255.0
ip inspect rule1 in
duplex auto
speed auto
!

   The filename of the router image, available via "show version"
   command, includes an "o" in the section between the hyphens, if the
   software includes the IOS Firewall Featureset, as in the following
   example.

   Router>show version
   Cisco Internetwork Operating System Software
   IOS (tm) C2600 Software (C2600-IO3-M), Version 12.1(5)T, RELEASE
   SOFTWARE (fc1)
   (the rest is truncated)

   In this example the image file name is c2600-io3-m. Since it has an
   "o" in its name, this image can support CBAC. For additional
   information regarding Cisco IOS image identifiers consult the document
   at http://www.cisco.com/warp/public/620/5.shtml#identifiers. The
   major affected Cisco IOS trains are:

     * 11.2P
     * 11.3T
     * 12.0, 12.0T
     * 12.1, 12.1T, 12.1E
     * 12.2, 12.2T

   In addition to these, several Early Deployment (also known as X
   releases) are affected. The complete list is given in the Software
   Versions and Fixes section of this advisory.

   Affected hardware models are:

     * Cisco routers in the following series: 800, 820, 950, 1400, 1600,
       1700, 2500, 2600, 3600, 4000 Gateway, 4224, 7100, 7200, 7400,
       7500, SOHO 70, ubr900, ICS7750.

     * The Catalyst 5000 and 6000 if they are running Cisco IOS software.

   No other Cisco products are affected.

Details

   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.

Impact

   By allowing packets of different type into the protected network, the
   customer is exposed to much bigger threat. This vulnerability can be
   expoited for recoinassance purposes, but only for a single port and
   host that initiated a sesion 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.

Software Versions and Fixes

Obtaining Fixed Software

   Cisco is offering free software upgrades to eliminate this
   vulnerability for all affected customers.

   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
   Web site at http://www.cisco.com.

   Customers whose Cisco products are provided or maintained through
   prior or existing agreement with third-party support organizations
   such as Cisco Partners, authorized resellers, or service providers
   should contact that support organization for assistance with the
   upgrade, which should be free of charge.

   Customers who purchase direct from Cisco but who do not hold a Cisco
   service contract and customers who purchase through third party
   vendors but are unsuccessful at obtaining fixed software through their
   point of sale should get their 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

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

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

Workarounds

There is no workaround.

Exploitation and Public Announcements

   This vulnerability was discovered by a customer. 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 is a final notice. Although Cisco cannot guarantee the accuracy
   of all statements in this notice, all of the facts have been checked
   to the best of our ability. Cisco does not anticipate issuing updated
   versions of this notice unless there is some material change in the
   facts. Should there be a significant change in the facts, Cisco may
   update this notice.

   A standalone copy or paraphrase of the text of this security advisory
   that omits the distribution URL in the following section is an
   uncontrolled copy, and may lack important information or contain
   factual errors.

Distribution

   This notice will be posted on Cisco's Worldwide Web site at
   http://www.cisco.com/warp/public/707/IOS-cbac-dynacl-pub.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
     * 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 notice, if any, will be placed on Cisco's
   Worldwide Web server, but may or may not be actively announced on
   mailing lists or newsgroups. Users concerned about this problem are
   encouraged to check the URL given above for any updates.

Revision History

Revision 1.0 2001-November-28 08:00 GMT-0800 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 Web site at
   http://www.cisco.com/warp/public/707/sec_incident_response.shtml.
   This includes instructions for press inquiries regarding Cisco
   security notices.

   All Cisco Security Advisories are available at
   http://www.cisco.com/go/psirt
     _________________________________________________________________

   This notice is Copyright 2001 by Cisco Systems, Inc. This notice may
   be redistributed freely after the release date given at the top of the
   text, provided that redistributed copies are complete and unmodified,
   and include all date and version information.
     _________________________________________________________________

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Next message: Travis Pugh: "Re: Pix info - audit info and logging and general"
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