Cisco IOS cTCP Denial of Service Vulnerability

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Updated:May 31, 2014
Document ID:1454798227195141

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Cisco Security Advisory

Cisco IOS cTCP Denial of Service Vulnerability

High
Advisory ID:
cisco-sa-20090325-ctcp
First Published:
2009 March 25 16:00 GMT
Version 1.1:
Final
Workarounds:
See below
Cisco Bug IDs:
CSCsr16693
CSCsu21828
CVE-2009-0635
CVSS Score:
Base 7.8, Temporal 6.4Click Icon to Copy Verbose Score
AV:N/AC:L/Au:N/C:N/I:N/A:C/E:F/RL:OF/RC:C
CVE-2009-0635

Summary

Affected Products

  • Vulnerable Products

    Cisco IOS devices running versions 12.4(9)T or later and configured for Cisco Tunneling Control Protocol (cTCP) encapsulation for EZVPN server are vulnerable.

    Note: The cTCP encapsulation feature was introduced in Cisco IOS version 12.4(9)T. The cTCP encapsulation feature is disabled by default. Cisco IOS devices configured for EZVPN client are not affected by this vulnerability. Only devices configured as EZVPN servers are vulnerable.

    To configure the cTCP encapsulation feature for Easy VPN, use the crypto ctcp command in global configuration mode. You can optionally specify the port number that the device will listen to with the crypto ctcp port <port> command. Up to ten numbers can be configured and the port value can be from 1 through 65535. If the port keyword is not configured, the default port number is 10000. In the following example, the Cisco IOS device is configured to listen for cTCP messages on port 10000.

    crypto ctcp port 10000

    Note: The port keyword is configured only on the Cisco IOS device acting as an EZVPN server.

    To determine the version of the 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 Cisco IOS Software release 12.3(26) with an installed image name of C2500-IS-L:

        Router#show version
    Cisco Internetwork Operating System Software
    IOS (tm) 2500 Software (C2500-IS-L), Version 12.3(26), RELEASE SOFTWARE (fc2)
    Technical Support: http://www.cisco.com/techsupport
    Copyright (c) 1986-2008 by cisco Systems, Inc.
    Compiled Mon 17-Mar-08 14:39 by dchih

  <output truncated>

    The next example shows a product running Cisco IOS Software release 12.4(20)T with an image name of C1841-ADVENTERPRISEK9-M:

        Router#show version
    Cisco IOS Software, 1841 Software (C1841-ADVENTERPRISEK9-M), Version 12.4(20)T, RELEASE SOFTWARE (fc3)
    Technical Support: http://www.cisco.com/techsupport
    Copyright (c) 1986-2008 by Cisco Systems, Inc.
    Compiled Thu 10-Jul-08 20:25 by prod_rel_team

  <output truncated>

    Additional information on the Cisco IOS release naming conventions can be found on the document entitled "White Paper: Cisco IOS Reference Guide", which is available at http://www.cisco.com/warp/public/620/1.html.

    Products Confirmed Not Vulnerable

    Cisco IOS devices that are not configured for cTCP are not affected by this vulnerability. The Cisco ASA and Cisco VPN 3000 series concentrators are not vulnerable. Cisco IOS devices configured as EZVPN clients are not affected by this vulnerability. The Cisco VPN Client is not vulnerable. Cisco IOS-XR and Cisco IOS-XE software are not affected by this vulnerability. No other Cisco products are currently known to be affected by this vulnerability.

Details

  • The Cisco Tunneling Control Protocol (cTCP) feature is used by Easy VPN remote device operating in an environment in which standard IPSec does not function transparently without modification to existing firewall rules. The cTCP traffic is actually TCP traffic. Cisco IOS cTCP packets are Internet Key Exchange (IKE) or Encapsulating Security Payload (ESP) packets that are being transmitted over TCP.

    A vulnerability exists where a series of TCP packets may cause a Cisco IOS device that is configured as an Easy VPN server with the cTCP encapsulation feature to run out of memory. This vulnerability is documented in Cisco Bug IDs CSCsr16693 ( registered customers only) and CSCsu21828 ( registered customers only) ; and has been assigned the Common Vulnerabilities and Exposures (CVE) identifier CVE-2009-0635.

Workarounds

  • No workarounds are available.

    As an alternative, the IPSec NAT traversal (NAT-T) feature can be used. The IPSec NAT-T feature introduces support for IP Security (IPSec) traffic to travel through Network Address Translation (NAT) or Port Address Translation (PAT) points in the network by addressing many known incompatabilites between NAT and IPSec.

    Note: The NAT-T feature was introduced in Cisco IOS version 12.2(13)T.

    NAT Traversal is a feature that is auto detected by VPN devices. There are no configuration steps for a router running Cisco IOS Release 12.2(13)T and later. If both VPN devices are NAT-T capable, NAT Traversal is auto-detected and auto-negotiated.

    Note: When you enable NAT-T, the Cisco IOS device automatically opens UDP port 4500 on all IPSec enabled interfaces.

    Caution: Be aware that you may need to enable IPSec over UDP on Cisco VPN software clients to support NAT-T. Additionally, you may need to change firewall rules to allow UDP port 500 for Internet Key Exchange (IKE) and UDP port 4500 for NAT-T.

    For more information about NAT-T, refer to the white paper at:

    http://www.cisco.com/en/US/docs/ios/security/configuration/guide/sec_ipsec_nat_transp.html

    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, which is available at the following link:

    https://sec.cloudapps.cisco.com/security/center/content/CiscoAppliedMitigationBulletin/cisco-amb-20090325-ctcp

Fixed Software

  • 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) names a Cisco IOS release train. If a given release train is vulnerable, then the earliest possible releases that contain the fix (along with the anticipated date of availability for each, if applicable) are listed in the "First Fixed Release" column of the table. The "Recommended Release" column indicates the releases which have fixes for all the published vulnerabilities at the time of this Advisory. 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. Cisco recommends upgrading to a release equal to or later than the release in the "Recommended Releases" column of the table.

    Major Release

    Availability of Repaired Releases

    Affected 12.0-Based Releases

    First Fixed Release

    Recommended Release

    There are no affected 12.0 based releases

    Affected 12.1-Based Releases

    First Fixed Release

    Recommended Release

    There are no affected 12.1 based releases

    Affected 12.2-Based Releases

    First Fixed Release

    Recommended Release

    There are no affected 12.2 based releases

    Affected 12.3-Based Releases

    First Fixed Release

    Recommended Release

    There are no affected 12.3 based releases

    Affected 12.4-Based Releases

    First Fixed Release

    Recommended Release

    12.4

    Not Vulnerable

    		  

    12.4JA

    Not Vulnerable

    		  

    12.4JDA

    Not Vulnerable

    		  

    12.4JK

    Not Vulnerable

    		  

    12.4JL

    Not Vulnerable

    		  

    12.4JMA

    Not Vulnerable

    		  

    12.4JMB

    Not Vulnerable

    		  

    12.4JX

    Not Vulnerable

    		  

    12.4MD

    Not Vulnerable

    		  

    12.4MR

    Not Vulnerable

    		  

    12.4SW

    Not Vulnerable

    		  

    12.4T

    12.4(20)T2

    12.4(15)T9; Available on 29-APR-2009

    12.4(22)T1

    12.4(15)T9; Available on 29-APR-2009

    12.4XA

    Not Vulnerable

    		  

    12.4XB

    Not Vulnerable

    		  

    12.4XC

    Not Vulnerable

    		  

    12.4XD

    Not Vulnerable

    		  

    12.4XE

    Not Vulnerable

    		  

    12.4XF

    Not Vulnerable

    		  

    12.4XG

    Not Vulnerable

    		  

    12.4XJ

    Not Vulnerable

    		  

    12.4XK

    Not Vulnerable

    		  

    12.4XL

    Not Vulnerable

    		  

    12.4XM

    Not Vulnerable

    		  

    12.4XN

    Not Vulnerable

    		  

    12.4XP

    Not Vulnerable

    		  

    12.4XQ

    Not Vulnerable

    		  

    12.4XR

    Not Vulnerable

    		  

    12.4XT

    Not Vulnerable

    		  

    12.4XV

    Not Vulnerable

    		  

    12.4XW

    Not Vulnerable

    		  

    12.4XY

    Not Vulnerable

    		  

    12.4XZ

    12.4(15)XZ2

    12.4(15)XZ2

    12.4YA

    12.4(20)YA2

    12.4(20)YA3

    12.4YB

    Not Vulnerable

    		  

    12.4YD

    Not Vulnerable

    		  

Exploitation and Public Announcements

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

    This vulnerability was found during the resolution of a technical support service request.

Cisco Security Vulnerability Policy

  • To learn about Cisco security vulnerability disclosure policies and publications, see the Security Vulnerability Policy. This document also contains instructions for obtaining fixed software and receiving security vulnerability information from Cisco.

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Revision History

  • Revision 1.1

    2009-June-25

    Removed references to the March/09 combined fixed software table.

    Revision 1.0

    2009-March-25

    Initial public release.

    Show Less

Cisco Security Vulnerability Policy

  • To learn about Cisco security vulnerability disclosure policies and publications, see the Security Vulnerability Policy. This document also contains instructions for obtaining fixed software and receiving security vulnerability information from Cisco.

Subscribe to Cisco Security Notifications

Action Links for This Advisory

Related to This Advisory