Cisco Security Advisory

DLSw Vulnerability

Advisory ID: cisco-sa-20070110-dlsw

http://tools.cisco.com/security/center/content/CiscoSecurityAdvisory/cisco-sa-20070110-dlsw

Revision 1.2

For Public Release 2007 January 10 16:00  UTC (GMT)


Summary

A vulnerability exists in the Data-link Switching (DLSw) feature in Cisco IOS where an invalid value in a DLSw message could result in a reload of the DLSw device. Successful exploitation of this vulnerability requires that an attacker be able to establish a DLSw connection to the device.

There are workarounds available for this vulnerability, as detailed in the Workarounds section below.

This advisory is posted at http://tools.cisco.com/security/center/content/CiscoSecurityAdvisory/cisco-sa-20070110-dlsw

Affected Products

Vulnerable Products

This security advisory applies to all Cisco products that run Cisco IOS Software versions 11.0 through 12.4 configured for DLSw. A system which contains the DLSw feature, but does not have it enabled, is not affected.

A router which is configured for DLSw will have a line in the configurations defining a local DLSw peer. This definition can be seen by issuing the command show running-config and looking for lines similar to the following:

dlsw local-peer peer-id 

To determine if DLSw is enabled on your Cisco IOS device, it is also possible to issue the show dlsw statistics command while in enable mode and look for output similar to:

Router#show dlsw statistics
DLSw+ Control Queue Statistics:
 SNA Control Queue (count/max/dropped):     (0/0/0)
 Netbios Control Queue (count/max/dropped): (0/0/0)
 Other Control Queue (count/max/dropped):   (0/100/0)
 Critical Control Queue (count/max):        (0/0)

DLSw+ Border Peer Caching Statistics:

       0 Border Peer Frames processed
       0 Border frames found Local
       0 Border frames found Remote
       0 Border frames found Group Cache

A device which is not configured for DLSw will simply return to a command prompt with no output.

A device which does not support the DLSw feature will return output similar to:

Router#show dlsw statistics
              ^
% Invalid input detected at '^' marker.

Any version of Cisco IOS prior to the versions which will be listed in the Software Versions and Fixes section below may be vulnerable.

To determine the version of Cisco IOS software running on a Cisco product, log in to the device and issue the show version command to display the system banner. Cisco IOS Software will identify itself as "Internetwork Operating System Software" or simply "IOS". On the next line of output, the image name will be displayed between parentheses, followed by "Version" and the IOS release name. Other Cisco devices will not have the show version command or will give different output.

The following example identifies a Cisco product running IOS release 12.3(6) with an installed image name of C3640-I-M:

Cisco Internetwork Operating System Software
IOS (tm) 3600 Software (C3640-I-M), Version 12.3(6), RELEASE SOFTWARE (fc3)

The next example shows a product running IOS release 12.3(11)T3 with an image name of C3845-ADVIPSERVICESK9-M:

Cisco IOS Software, 3800 Software (C3845-ADVIPSERVICESK9-M), Version 12.3(11)T3,
 RELEASE SOFTWARE (fc4)
Technical Support: http://www.cisco.com/techsupport
Copyright (c) 1986-2005 by Cisco Systems, Inc.

Additional information about Cisco IOS release naming can be found at http://www.cisco.com/warp/public/620/1.html.

No other Cisco products are currently known to be affected by the vulnerability addressed in this advisory.

Products Confirmed Not Vulnerable

Products confirmed not to be vulnerable include devices which are not configured for DLSw.

Details

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

Vulnerability Scoring Details

Impact

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

Software Versions and Fixes

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


Workarounds

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://tools.cisco.com/security/center/content/CiscoAppliedMitigationBulletin/cisco-amb-20070110-dlsw

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.

Obtaining Fixed Software

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.

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 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.

Customers Without Service Contracts

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.

Exploitation and Public Announcements

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

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-20070110-dlsw

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 1.2

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

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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