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Cisco Security Advisory: Cisco IOS cTCP Denial of Service
Vulnerability

Advisory ID: cisco-sa-20090325-ctcp

http://www.cisco.com/warp/public/707/cisco-sa-20090325-ctcp.shtml 

Revision 1.0

For Public Release 2009 March 25 1600 UTC (GMT)

- ---------------------------------------------------------------------

Summary
======
A series of TCP packets may cause a denial of service (DoS) condition
on Cisco IOS devices that are configured as Easy VPN servers with the
Cisco Tunneling Control Protocol (cTCP) encapsulation feature. Cisco
has released free software updates that address this vulnerability.
No workarounds are available; however, the IPSec NAT traversal
(NAT-T) feature can be used as an alternative.

This advisory is posted at 
http://www.cisco.com/warp/public/707/cisco-sa-20090325-ctcp.shtml 

Note: The March 25, 2009, Cisco IOS Security Advisory bundled
publication includes eight Security Advisories. All of the advisories
address vulnerabilities in Cisco IOS Software. Each advisory lists
the releases that correct the vulnerability or vulnerabilities in the
advisory. The following table lists releases that correct all Cisco
IOS Software vulnerabilities that have been published in Cisco
Security Advisories on March 25, 2009, or earlier.

http://www.cisco.com/warp/public/707/cisco-sa-20090325-bundle.shtml 

Individual publication links are listed below:

  * Cisco IOS cTCP Denial of Service Vulnerability
http://www.cisco.com/warp/public/707/cisco-sa-20090325-ctcp.shtml 

  * Cisco IOS Software Multiple Features IP Sockets Vulnerability
http://www.cisco.com/warp/public/707/cisco-sa-20090325-ip.shtml 

  * Cisco IOS Software Mobile IP and Mobile IPv6 Vulnerabilities
http://www.cisco.com/warp/public/707/cisco-sa-20090325-mobileip.shtml 

  * Cisco IOS Software Secure Copy Privilege Escalation Vulnerability
http://www.cisco.com/warp/public/707/cisco-sa-20090325-scp.shtml 

  * Cisco IOS Software Session Initiation Protocol Denial of Service
    Vulnerability
http://www.cisco.com/warp/public/707/cisco-sa-20090325-sip.shtml 

  * Cisco IOS Software Multiple Features Crafted TCP Sequence
    Vulnerability
http://www.cisco.com/warp/public/707/cisco-sa-20090325-tcp.shtml 

  * Cisco IOS Software Multiple Features Crafted UDP Packet
    Vulnerability
http://www.cisco.com/warp/public/707/cisco-sa-20090325-udp.shtml 

  * Cisco IOS Software WebVPN and SSLVPN Vulnerabilities
http://www.cisco.com/warp/public/707/cisco-sa-20090325-webvpn.shtml 

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  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

      



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

      


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 and CSCsu21828; and has 
been assigned the Common Vulnerabilities and Exposures (CVE) 
identifier CVE-2009-0635.

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. 

CSCsr16693 - cTCP server may crash when processing a series of TCP
             packets

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

CSCsu21828 - Cisco IOS Device may crash with cTCP enabled

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 this vulnerability may cause the affected
device to run out of memory. Repeated exploitation will result in a
denial of service (DoS) condition.

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) 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        | First Fixed Release   | Recommended Release   |
| Releases          |                       |                       |
|-------------------------------------------------------------------|
| There are no affected 12.0 based releases                         |
|-------------------------------------------------------------------|
| Affected          |                       |                       |
| 12.1-Based        | First Fixed Release   | Recommended Release   |
| Releases          |                       |                       |
|-------------------------------------------------------------------|
| There are no affected 12.1 based releases                         |
|-------------------------------------------------------------------|
| Affected          |                       |                       |
| 12.2-Based        | First Fixed Release   | Recommended Release   |
| Releases          |                       |                       |
|-------------------------------------------------------------------|
| There are no affected 12.2 based releases                         |
|-------------------------------------------------------------------|
| Affected          |                       |                       |
| 12.3-Based        | First Fixed Release   | Recommended Release   |
| Releases          |                       |                       |
|-------------------------------------------------------------------|
| There are no affected 12.3 based releases                         |
|-------------------------------------------------------------------|
| Affected          |                       |                       |
| 12.4-Based        | First Fixed Release   | Recommended Release   |
| Releases          |                       |                       |
|-------------------+-----------------------+-----------------------|
| 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        |                       |
|-------------------+-----------------------+-----------------------|
|                   | 12.4(20)T2            | 12.4(22)T1            |
| 12.4T             |                       |                       |
|                   | 12.4(15)T9; Available | 12.4(15)T9; Available |
|                   | on 29-APR-2009        | 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        |                       |
+-------------------------------------------------------------------+

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:

http://www.cisco.com/warp/public/707/cisco-amb-20090325-ctcp.shtml 

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/docs/general/warranty/English/EU1KEN_.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/en/US/support/tsd_cisco_worldwide_contacts.html 
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.

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

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-20090325-ctcp.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-bulletins@lists.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 |               | Initial    |
| 1.0      | 2009-March-25 | 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/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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