Cisco Security Advisory: DLSw Vulnerability

Vulnerable Products

Products Confirmed Not Vulnerable

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Data-link switching (DLSw) provides a means of transporting IBM Systems Network Architecture (SNA) and network basic input/output system (NetBIOS) traffic over an IP network.

Establishing DLSw communications involves several operational stages.

1. In phase one, DLSw peers establish two TCP connections with each other via TCP ports 2065 or 2067. Those TCP connections provide the foundation for the DLSw communication.
   
2. After a connection is established, the DLSw partners exchange a list of supported capabilities in phase two. This helps to ensure that the peers use the same options. This is particularly vital when the DLSw partners are manufactured by different vendors.
   
3. Next, the DLSw partners establish circuits between SNA or NetBIOS end systems, and information frames can flow over the circuit.
   

A vulnerability exists in certain Cisco IOS software releases when configured for DLSw. After the connection is established, it is possible for a reload to occur should the device receive an invalid option during the capabilities exchange.

This vulnerability is documented in Cisco Bug ID CSCsf28840 ( registered customers only) .

Vulnerability Scoring Details

Cisco is providing scores for the vulnerabilities in this advisory based on the Common Vulnerability Scoring System (CVSS).

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

Cisco PSIRT will set the bias in all cases to normal. Customers are encouraged to apply the bias parameter when determining the environmental impact of a particular vulnerability.

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

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.

CSCsf28840 ( registered customers only)
CVSS Base Score - 3.3
Access Vector	Access Complexity	Authentication	Confidentiality Impact	Integrity Impact	Availability Impact	Impact Bias
Remote	Low	Not Required	None	None	Complete	Normal
CVSS Temporal Score - 2.7
Exploitability		Remediation Level		Report Confidence
Functional		Official Fix		Confirmed

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Successful exploitation of the vulnerability may result in a reload of the device.

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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.

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" 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).

For more information on the terms "Rebuild" and "Maintenance," consult the following URL: http://www.cisco.com/warp/public/620/1.html.

Major Release	Availability of Repaired Releases
Affected 12.0-Based Release	Rebuild	Maintenance
12.0	Vulnerable; migrate to 12.2(46); available 10-May-07
12.0S		12.0(18)S
12.0SZ	Vulnerable; migrate to 12.0(23)S or later
12.0T	Vulnerable; migrate to 12.2(46); available 10-May-07
12.0WC	12.0(5)WC17
12.0XA	Vulnerable; migrate to 12.2(46); available 10-May-07
12.0XC	Vulnerable; migrate to 12.2(46); available 10-May-07
12.0XD	Vulnerable; migrate to 12.2(46); available 10-May-07
12.0XE	Vulnerable; migrate to 12.1(26)E8
12.0XG	Vulnerable; migrate to 12.2(46); available 10-May-07
12.0XH	Vulnerable; migrate to 12.2(46); available 10-May-07
12.0XI	Vulnerable; migrate to 12.2(46); available 10-May-07
12.0XJ	12.0(4)XJ5
12.0XK	Vulnerable; migrate to 12.2(46); available 10-May-07
12.0XN	Vulnerable; migrate to 12.2(46); available 10-May-07
12.0XQ	Vulnerable; migrate to 12.2(46); available 10-May-07
12.0XR	Vulnerable; migrate to 12.2(46); available 10-May-07
12.0XT	Vulnerable; contact TAC
Affected 12.1-Based Release	Rebuild	Maintenance
12.1	Vulnerable; migrate to 12.2(46); available 10-May-07
12.1AA	Vulnerable; migrate to 12.2(46); available 10-May-07
12.1E	12.1(26)E8
	12.1(27b)E2; available 25-Jun-07
12.1EC	Vulnerable; migrate to 12.2(4)BC1 or later
12.1EX	Vulnerable; migrate to 12.1(26)E8
12.1EZ	Vulnerable; migrate to 12.1(26)E8
12.1T	Vulnerable; migrate to 12.2(46); available 10-May-07
12.1XA	Vulnerable; migrate to 12.2(46); available 10-May-07
12.1XC	Vulnerable; migrate to 12.2(46); available 10-May-07
12.1XD	Vulnerable; migrate to 12.2(46); available 10-May-07
12.1XE	12.1(1)XE1
12.1XG	Vulnerable; migrate to 12.3(21) or later
12.1XH	Vulnerable; migrate to 12.2(46); available 10-May-07
12.1XI	Vulnerable; migrate to 12.2(46); available 10-May-07
12.1XJ	Vulnerable; migrate to 12.3(21) or later
12.1XM	Vulnerable; migrate to 12.3(21) or later
12.1XP	Vulnerable; migrate to 12.3(21) or later
12.1XQ	Vulnerable; migrate to 12.3(21) or later
12.1XS	Vulnerable; migrate to 12.2(46); available 10-May-07
12.1XT	12.1(3)XT2
12.1XV	12.1(5)XV1
12.1XW	Vulnerable; migrate to 12.2(46); available 10-May-07
12.1XX	Vulnerable; migrate to 12.2(46); available 10-May-07
12.1XY	Vulnerable; migrate to 12.2(46); available 10-May-07
12.1XZ	Vulnerable; migrate to 12.2(46); available 10-May-07
12.1YA	Vulnerable; migrate to 12.3(21) or later
12.1YB	Vulnerable; migrate to 12.3(21) or later
12.1YD	Vulnerable; migrate to 12.3(21) or later
12.1YI	Vulnerable; migrate to 12.3(21) or later
Affected 12.2-Based Release	Rebuild	Maintenance
12.2		12.2(46); available 10-May-07
12.2B	Vulnerable; migrate to 12.4(12) or later
12.2BW	Vulnerable; migrate to 12.3(21) or later
12.2BY	Vulnerable; migrate to 12.4(12) or later
12.2DD	Vulnerable; migrate to 12.4(12) or later
12.2DX	Vulnerable; migrate to 12.4(12) or later
12.2IXA	Vulnerable; migrate to 12.2(18)IXC or later
12.2IXB	Vulnerable; migrate to 12.2(18)IXC or later
12.2MC	Vulnerable; migrate to 12.4(12) or later
12.2S		12.2(30)S
12.2SB	12.2(28)SB6
	12.2(31)SB2
12.2SBC	Vulnerable; migrate to 12.2(31)SB2 or later
12.2SRA	12.2(33)SRA2
12.2SU	Vulnerable; migrate to 12.4(12) or later
12.2SV		12.2(26)SV
12.2SW	12.2(25)SW9
12.2SX	Vulnerable; migrate to 12.2(18)SXE6b
12.2SXA	Vulnerable; migrate to 12.2(18)SXE6b
12.2SXB	Vulnerable; migrate to 12.2(18)SXE6b
12.2SXD	Vulnerable; migrate to 12.2(18)SXE6b
12.2SXE	12.2(18)SXE6b
12.2SXF	12.2(18)SXF8
12.2SY	Vulnerable; migrate to 12.2(18)SXE6b
12.2SZ	Vulnerable; migrate to 12.2(30)S or later
12.2T	Vulnerable; migrate to 12.3(21) or later
12.2TPC	Vulnerable; contact TAC
12.2XA	Vulnerable; migrate to 12.3(21) or later
12.2XB	12.2(2)XB17
12.2XC	Vulnerable; migrate to 12.4(12) or later
12.2XD	Vulnerable; migrate to 12.3(21) or later
12.2XG	Vulnerable; migrate to 12.3(21) or later
12.2XH	Vulnerable; migrate to 12.3(21) or later
12.2XJ	Vulnerable; migrate to 12.3(21) or later
12.2XK	Vulnerable; migrate to 12.3(21) or later
12.2XL	Vulnerable; migrate to 12.3(21) or later
12.2XM	Vulnerable; migrate to 12.3(21) or later
12.2XN	Vulnerable; migrate to 12.3(21) or later
12.2XQ	Vulnerable; migrate to 12.3(21) or later
12.2XT	Vulnerable; migrate to 12.3(21) or later
12.2XU	Vulnerable; migrate to 12.3(21) or later
12.2XV	Vulnerable; migrate to 12.3(21) or later
12.2XW	Vulnerable; migrate to 12.3(21) or later
12.2YA	12.2(4)YA10
12.2YB	Vulnerable; migrate to 12.3(21) or later
12.2YC	Vulnerable; migrate to 12.3(21) or later
12.2YD	Vulnerable; migrate to 12.4(12) or later
12.2YE	Vulnerable; migrate to 12.2(30)S or later
12.2YF	Vulnerable; migrate to 12.3(21) or later
12.2YH	Vulnerable; migrate to 12.3(21) or later
12.2YJ	12.2(8)YJ1
12.2YL	Vulnerable; migrate to 12.4(12) or later
12.2YM	Vulnerable; migrate to 12.4(12) or later
12.2YN	Vulnerable; migrate to 12.4(12) or later
12.2YT	Vulnerable; migrate to 12.3(21) or later
12.2YU	Vulnerable; migrate to 12.4(12) or later
12.2YV	12.2(11)YV1
12.2YW	Vulnerable; migrate to 12.4(12) or later
12.2YX	Vulnerable; migrate to 12.4(12) or later
12.2YY	Vulnerable; migrate to 12.4(12) or later
12.2YZ	Vulnerable; migrate to 12.2(30)S or later
12.2ZA	Vulnerable; migrate to 12.2(18)SXE6b
12.2ZB	Vulnerable; migrate to 12.4(12) or later
12.2ZD	Vulnerable; contact TAC
12.2ZE	Vulnerable; migrate to 12.3(21) or later
12.2ZF	Vulnerable; migrate to 12.4(12) or later
12.2ZH	12.2(13)ZH6
12.2ZJ	Vulnerable; migrate to 12.4(12) or later
12.2ZL	Vulnerable; contact TAC
12.2ZN	Vulnerable; migrate to 12.4(12) or later
12.2ZP	Migrate to 12.2(20)S7 or later
12.2ZU	Vulnerable; contact TAC
12.2ZV	12.2(28a)ZV1
12.2ZW	Vulnerable; migrate to 12.2(33)SRB
12.2ZX		12.2(28)ZX
Affected 12.3-Based Release	Rebuild	Maintenance
12.3		12.3(21)
12.3B	Vulnerable; migrate to 12.4(12) or later
12.3BW	Vulnerable; migrate to 12.4(12) or later
12.3T	Vulnerable; migrate to 12.4(12) or later
12.3XA	12.3(2)XA5
12.3XB	Vulnerable; migrate to 12.4(12) or later
12.3XC	12.3(2)XC3
12.3XD	Vulnerable; migrate to 12.4(12) or later
12.3XE	12.3(2)XE2
12.3XF	Vulnerable; migrate to 12.4(12) or later
12.3XG	Vulnerable; contact TAC
12.3XH	Vulnerable; migrate to 12.4(12) or later
12.3XI	12.3(7)XI8a
12.3XJ	Vulnerable; migrate to 12.4(11)T1
12.3XK	Vulnerable; migrate to 12.4(12) or later
12.3XQ	Vulnerable; migrate to 12.4(12) or later
12.3XR	Vulnerable; contact TAC
12.3XU	Vulnerable; migrate to 12.4(4)T7 or later
12.3XW	Vulnerable; migrate to 12.4(11)T1
12.3XX	12.3(8)XX2
12.3YF	Vulnerable; migrate to 12.4(11)T1
12.3YG	12.3(8)YG5
12.3YH	Vulnerable; migrate to 12.4(4)T7 or later
12.3YI	Vulnerable; migrate to 12.4(4)T7 or later
12.3YJ	Vulnerable; migrate to 12.4(6)T6 or later
12.3YK	Vulnerable; migrate to 12.4(4)T7 or later
12.3YM	Vulnerable; contact TAC
12.3YQ	Vulnerable; migrate to 12.4(6)T6 or later
12.3YT	Vulnerable; migrate to 12.4(4)T7 or later
12.3YU	Vulnerable; contact TAC
12.3YX	Vulnerable; migrate to 12.4(11)T1
12.3YZ	Vulnerable; contact TAC
Affected 12.4-Based Release	Rebuild	Maintenance
12.4	12.4(7d)
	12.4(8c)
	12.4(10a)	12.4(12)
12.4T	12.4(4)T7
	12.4(6)T6
	12.4(9)T3
	12.4(11)T1
12.4XA	Vulnerable; migrate to 12.4(6)T6 or later
12.4XB	Vulnerable; contact TAC
12.4XC	12.4(4)XC6
12.4XD	12.4(4)XD5
12.4XE	Vulnerable; contact TAC

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The effectiveness of any mitigation 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 mitigation or fix is the most appropriate for use in the intended network before it is deployed.

Additional mitigations that can be deployed on Cisco devices within the network are available in the Cisco Applied Mitigation Bulletin companion document for this advisory: http://www.cisco.com/warp/public/707/cisco-amb-20070110-dlsw.shtml

Configure Explicitly Defined DLSw Peers

If DLSw is configured with no remote peers defined, then it must be operating in promiscuous mode on one end of the connection. Promiscuous mode could allow for any device to attempt to establish a DLSw peer with the router. To prevent malicious connections, DLSw peers may be explicitly defined with the dlsw remote-peer command removing the need for promiscuous mode.

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Cisco will make free software available to address this vulnerability for affected customers. This advisory will be updated as fixed software becomes available. 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.

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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.

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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 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.

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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
  

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.

Refer to http://www.cisco.com/warp/public/687/Directory/DirTAC.shtml for additional TAC contact information, including special localized telephone numbers and instructions and e-mail addresses for use in various languages.

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This vulnerability was reported to Cisco by Martyn Ruks of MWR InfoSecurity and was originally presented at DEFCON in August 2006.

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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.

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This advisory is posted on Cisco's worldwide website at: http://www.cisco.com/warp/public/707/cisco-sa-20070110-dlsw.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.

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Revision 1.2	2007-April-20	Corrected release information and dates, especially for 12.2(46) fixes.
Revision 1.1	2007-January-12	Corrected release dates for 12.4(11)T1
Revision 1.0	2007-January-10	Initial public release

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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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