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Cisco Security Advisory: Cisco IOS Software Layer 2 Tunneling Protocol (L2TP) Denial of Service Vulnerability
From: Cisco Systems Product Security Incident Response Team <psirt () cisco com>
Date: Wed, 24 Sep 2008 17:50:00 +0200

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Hash: SHA1

Cisco Security Advisory: Cisco IOS Software Layer 2 Tunneling
Protocol (L2TP) Denial of Service Vulnerability

Advisory ID: cisco-sa-20080924-l2tp

http://www.cisco.com/warp/public/707/cisco-sa-20080924-l2tp.shtml

Revision 1.0

For Public Release 2008 September 24 1600 UTC (GMT)

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

Summary
=======

A vulnerability exists in the Cisco IOS software implementation of
Layer 2 Tunneling Protocol (L2TP), which affects limited Cisco IOS
software releases.

Several features enable the L2TP mgmt daemon process within Cisco IOS
software, including but not limited to Layer 2 virtual private
networks (L2VPN), Layer 2 Tunnel Protocol Version 3 (L2TPv3), Stack
Group Bidding Protocol (SGBP) and Cisco Virtual Private Dial-Up
Networks (VPDN). Once this process is enabled the device is
vulnerable.

This vulnerability will result in a reload of the device when
processing a specially crafted L2TP packet.

Cisco has released free software updates that address this
vulnerability.

Workarounds that mitigate this vulnerability are available.

This advisory is posted at 
http://www.cisco.com/warp/public/707/cisco-sa-20080924-l2tp.shtml

Note:  The September 24, 2008 IOS Advisory bundled publication
includes twelve Security Advisories. Eleven of the advisories address
vulnerabilities in Cisco's IOS software, and one advisory addresses
vulnerabilities in Cisco Unified Communications Manager. Each
Advisory lists the releases that correct the vulnerability described
in the Advisory. Please reference the following software table to
find a release that fixes all published IOS software Advisories as of
September 24th, 2008:

http://www.cisco.com/warp/public/707/cisco-sa-20080924-bundle.shtml

Individual publication links are listed below:

  * http://www.cisco.com/warp/public/707/cisco-sa-20080924-iosips.shtml
  * http://www.cisco.com/warp/public/707/cisco-sa-20080924-ssl.shtml
  * http://www.cisco.com/warp/public/707/cisco-sa-20080924-sip.shtml
  * http://www.cisco.com/warp/public/707/cisco-sa-20080924-cucm.shtml
  * http://www.cisco.com/warp/public/707/cisco-sa-20080924-vpn.shtml
  * http://www.cisco.com/warp/public/707/cisco-sa-20080924-mfi.shtml
  * http://www.cisco.com/warp/public/707/cisco-sa-20080924-ipc.shtml
  * http://www.cisco.com/warp/public/707/cisco-sa-20080924-ubr.shtml
  * http://www.cisco.com/warp/public/707/cisco-sa-20080924-multicast.shtml
  * http://www.cisco.com/warp/public/707/cisco-sa-20080924-sccp.shtml
  * http://www.cisco.com/warp/public/707/cisco-sa-20080924-iosfw.shtml

Affected Products
=================

All devices running affected versions of 12.2 or 12.4 Cisco IOS
system software and that have a vulnerable configuration are affected
by this vulnerability.

Vulnerable Products
+------------------

To determine if a device is vulnerable, first confirm that the device
is running an affected version of 12.2 or 12.4 Cisco IOS system
software. Then check for the process L2TP mgmt daemon running on the
device.

To determine the software version 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 that is running
Cisco IOS Software Release 12.4(11)T2:

    Router#show version
    Cisco IOS Software, 7200 Software (C7200-ADVSECURITYK9-M), Version 12.4(11)T2, RELEASE SOFTWARE (fc4)
    Technical Support: http://www.cisco.com/techsupport
    Copyright (c) 1986-2007 by Cisco Systems, Inc.
    Compiled Tue 01-May-07 04:19 by prod_rel_team


    <output truncated>


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

To check if the process L2TP mgmt daemon is running on a device, log
into the command line interface (CLI) and issue the command show
processes | include L2TP . (NOTE: The command is case sensitive.) If
the output returns a line with the process name L2TP mgmt daemon, the
device is vulnerable. The following example shows a device running
the L2TP mgmt daemon process:

    Router#show processes | include L2TP
     158 Mwe 62590FE4            4          3    133322900/24000  0 L2TP mgmt daemon
    Router#

The L2TP mgmt daemon is started by several different types of
configurations that may be deployed in networks that leverage the
L2TP protocol. If any of the following commands appear within a
device's configuration, show running-config, then the device will
have started the L2TP mgmt daemon and is vulnerable.

  * Device is configured with Virtual Private Dial-Up Networks
    (VPDN).
    The command vpdn enable will appear in the device configuration.
  * Device is configured for L2TP or L2TPv3 Client-Initiated VPDN
    Tunneling.
    The command pseudowire peer-ip-address vcid pw-class 
    pw-class-name " appears in the device configuration.
  * Device is configured with Stack Group Bidding Protocol (SGBP).
    The command sgbp group group-name will appear in the device
    configuration.
  * A L2TP signaling template has been defined.
    The command l2tp-class l2tp-class name will appear in the device
    configuration.
  * Devices configured for Layer 2 Tunnel Protocol Version 3
    The commands pseudowire-class pseudowire-class name and a
    successfully applied interface xconnect command will appear in
    the device configuration.

Products Confirmed Not Vulnerable
+--------------------------------

  * Devices that are running Cisco IOS versions that are not
    explicitly listed in the software table below as vulnerable, are
    not affected.
  * Cisco IOS XR is not affected.
  * Cisco IOS XE is not affected.

No other Cisco products are currently known to be affected by this
vulnerability.

Details
=======

Documented in RFC2661, L2TP and RFC3931, L2TPv3 are protocols for
tunneling network traffic between two peers over an existing network.

A device running affected 12.2 and 12.4 versions of Cisco IOS and
that has the L2TP mgmt daemon process running will reload when
processing a specially crafted L2TP packet.

Several features leverage the L2TP protocol and start the L2TP mgmt
daemon within Cisco IOS. These features have been outlined in this
advisory under the Vulnerable Products section.

This vulnerability is documented in Cisco bug ID CSCsh48879 
and Common Vulnerabilities and Exposures (CVE) identifier 
CVE-2008-3813 has been assigned to this vulnerability.

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

CSCsh48879 - Crafted L2TP packet triggers a device reload.

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 the vulnerability will result in a reload
of the device. Repeated exploitation may result in an extended 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     |         Availability of Repaired Releases          |
|   Release    |                                                    |
|--------------+----------------------------------------------------|
|   Affected   |                                   |  Recommended   |
|  12.0-Based  |        First Fixed Release        |    Release     |
|   Releases   |                                   |                |
|-------------------------------------------------------------------|
| There are no affected 12.0 based releases                         |
|-------------------------------------------------------------------|
|   Affected   |                                   |  Recommended   |
|  12.1-Based  |        First Fixed Release        |    Release     |
|   Releases   |                                   |                |
|-------------------------------------------------------------------|
| There are no affected 12.1 based releases                         |
|-------------------------------------------------------------------|
|   Affected   |                                   |  Recommended   |
|  12.2-Based  |        First Fixed Release        |    Release     |
|   Releases   |                                   |                |
|--------------+-----------------------------------+----------------|
| 12.2         | Not Vulnerable                    |                |
|--------------+-----------------------------------+----------------|
| 12.2B        | Not Vulnerable                    |                |
|--------------+-----------------------------------+----------------|
| 12.2BC       | Not Vulnerable                    |                |
|--------------+-----------------------------------+----------------|
| 12.2BW       | Not Vulnerable                    |                |
|--------------+-----------------------------------+----------------|
| 12.2BX       | Not Vulnerable                    |                |
|--------------+-----------------------------------+----------------|
| 12.2BY       | Not Vulnerable                    |                |
|--------------+-----------------------------------+----------------|
| 12.2BZ       | Not Vulnerable                    |                |
|--------------+-----------------------------------+----------------|
| 12.2CX       | Not Vulnerable                    |                |
|--------------+-----------------------------------+----------------|
| 12.2CY       | Not Vulnerable                    |                |
|--------------+-----------------------------------+----------------|
| 12.2CZ       | Not Vulnerable                    |                |
|--------------+-----------------------------------+----------------|
| 12.2DA       | Not Vulnerable                    |                |
|--------------+-----------------------------------+----------------|
| 12.2DD       | Not Vulnerable                    |                |
|--------------+-----------------------------------+----------------|
| 12.2DX       | Not Vulnerable                    |                |
|--------------+-----------------------------------+----------------|
| 12.2EW       | Not Vulnerable                    |                |
|--------------+-----------------------------------+----------------|
| 12.2EWA      | Not Vulnerable                    |                |
|--------------+-----------------------------------+----------------|
| 12.2EX       | Not Vulnerable                    |                |
|--------------+-----------------------------------+----------------|
| 12.2EY       | Not Vulnerable                    |                |
|--------------+-----------------------------------+----------------|
| 12.2EZ       | Not Vulnerable                    |                |
|--------------+-----------------------------------+----------------|
| 12.2FX       | Not Vulnerable                    |                |
|--------------+-----------------------------------+----------------|
| 12.2FY       | Not Vulnerable                    |                |
|--------------+-----------------------------------+----------------|
| 12.2FZ       | Not Vulnerable                    |                |
|--------------+-----------------------------------+----------------|
| 12.2IRB      | Not Vulnerable                    |                |
|--------------+-----------------------------------+----------------|
| 12.2IXA      | Not Vulnerable                    |                |
|--------------+-----------------------------------+----------------|
| 12.2IXB      | Not Vulnerable                    |                |
|--------------+-----------------------------------+----------------|
| 12.2IXC      | Not Vulnerable                    |                |
|--------------+-----------------------------------+----------------|
| 12.2IXD      | Not Vulnerable                    |                |
|--------------+-----------------------------------+----------------|
| 12.2IXE      | Not Vulnerable                    |                |
|--------------+-----------------------------------+----------------|
| 12.2IXF      | Not Vulnerable                    |                |
|--------------+-----------------------------------+----------------|
| 12.2IXG      | Not Vulnerable                    |                |
|--------------+-----------------------------------+----------------|
| 12.2JA       | Not Vulnerable                    |                |
|--------------+-----------------------------------+----------------|
| 12.2JK       | Not Vulnerable                    |                |
|--------------+-----------------------------------+----------------|
| 12.2MB       | Not Vulnerable                    |                |
|--------------+-----------------------------------+----------------|
| 12.2MC       | Not Vulnerable                    |                |
|--------------+-----------------------------------+----------------|
| 12.2S        | Not Vulnerable                    |                |
|--------------+-----------------------------------+----------------|
| 12.2SB       | Not Vulnerable                    |                |
|--------------+-----------------------------------+----------------|
| 12.2SBC      | Not Vulnerable                    |                |
|--------------+-----------------------------------+----------------|
| 12.2SCA      | Not Vulnerable                    |                |
|--------------+-----------------------------------+----------------|
|              | Note: Releases prior to 12.2(37)  |                |
| 12.2SE       | SE are not vulnerable. First      | 12.2(46)SE     |
|              | fixed in 12.2(44)SE               |                |
|--------------+-----------------------------------+----------------|
| 12.2SEA      | Not Vulnerable                    |                |
|--------------+-----------------------------------+----------------|
| 12.2SEB      | Not Vulnerable                    |                |
|--------------+-----------------------------------+----------------|
| 12.2SEC      | Not Vulnerable                    |                |
|--------------+-----------------------------------+----------------|
| 12.2SED      | Not Vulnerable                    |                |
|--------------+-----------------------------------+----------------|
| 12.2SEE      | Not Vulnerable                    |                |
|--------------+-----------------------------------+----------------|
| 12.2SEF      | Not Vulnerable                    |                |
|--------------+-----------------------------------+----------------|
| 12.2SEG      | Not Vulnerable                    |                |
|--------------+-----------------------------------+----------------|
|              | Note: Releases prior to 12.2(37)  |                |
| 12.2SG       | SG are not vulnerable. First      | 12.2(46)SG1    |
|              | Fixed in 12.2(44)SG               |                |
|--------------+-----------------------------------+----------------|
| 12.2SGA      | Not Vulnerable                    |                |
|--------------+-----------------------------------+----------------|
| 12.2SL       | Not Vulnerable                    |                |
|--------------+-----------------------------------+----------------|
| 12.2SM       | Not Vulnerable                    |                |
|--------------+-----------------------------------+----------------|
| 12.2SO       | Not Vulnerable                    |                |
|--------------+-----------------------------------+----------------|
| 12.2SRA      | Not Vulnerable                    |                |
|--------------+-----------------------------------+----------------|
| 12.2SRB      | 12.2(33)SRB1                      | 12.2(33)SRB4   |
|--------------+-----------------------------------+----------------|
| 12.2SRC      | Not Vulnerable                    |                |
|--------------+-----------------------------------+----------------|
| 12.2SU       | Not Vulnerable                    |                |
|--------------+-----------------------------------+----------------|
| 12.2SV       | Not Vulnerable                    |                |
|--------------+-----------------------------------+----------------|
| 12.2SVA      | Not Vulnerable                    |                |
|--------------+-----------------------------------+----------------|
| 12.2SVC      | Not Vulnerable                    |                |
|--------------+-----------------------------------+----------------|
| 12.2SVD      | Not Vulnerable                    |                |
|--------------+-----------------------------------+----------------|
| 12.2SW       | Not Vulnerable                    |                |
|--------------+-----------------------------------+----------------|
| 12.2SX       | Not Vulnerable                    |                |
|--------------+-----------------------------------+----------------|
| 12.2SXA      | Not Vulnerable                    |                |
|--------------+-----------------------------------+----------------|
| 12.2SXB      | Not Vulnerable                    |                |
|--------------+-----------------------------------+----------------|
| 12.2SXD      | Not Vulnerable                    |                |
|--------------+-----------------------------------+----------------|
| 12.2SXE      | Not Vulnerable                    |                |
|--------------+-----------------------------------+----------------|
| 12.2SXF      | Not Vulnerable                    |                |
|--------------+-----------------------------------+----------------|
| 12.2SXH      | Not Vulnerable                    |                |
|--------------+-----------------------------------+----------------|
| 12.2SY       | Not Vulnerable                    |                |
|--------------+-----------------------------------+----------------|
| 12.2SZ       | Not Vulnerable                    |                |
|--------------+-----------------------------------+----------------|
| 12.2T        | Not Vulnerable                    |                |
|--------------+-----------------------------------+----------------|
| 12.2TPC      | Not Vulnerable                    |                |
|--------------+-----------------------------------+----------------|
| 12.2XA       | Not Vulnerable                    |                |
|--------------+-----------------------------------+----------------|
| 12.2XB       | Not Vulnerable                    |                |
|--------------+-----------------------------------+----------------|
| 12.2XC       | Not Vulnerable                    |                |
|--------------+-----------------------------------+----------------|
| 12.2XD       | Not Vulnerable                    |                |
|--------------+-----------------------------------+----------------|
| 12.2XE       | Not Vulnerable                    |                |
|--------------+-----------------------------------+----------------|
| 12.2XF       | Not Vulnerable                    |                |
|--------------+-----------------------------------+----------------|
| 12.2XG       | Not Vulnerable                    |                |
|--------------+-----------------------------------+----------------|
| 12.2XH       | Not Vulnerable                    |                |
|--------------+-----------------------------------+----------------|
| 12.2XI       | Not Vulnerable                    |                |
|--------------+-----------------------------------+----------------|
| 12.2XJ       | Not Vulnerable                    |                |
|--------------+-----------------------------------+----------------|
| 12.2XK       | Not Vulnerable                    |                |
|--------------+-----------------------------------+----------------|
| 12.2XL       | Not Vulnerable                    |                |
|--------------+-----------------------------------+----------------|
| 12.2XM       | Not Vulnerable                    |                |
|--------------+-----------------------------------+----------------|
| 12.2XN       | Not Vulnerable                    |                |
|--------------+-----------------------------------+----------------|
| 12.2XNA      | Not Vulnerable                    |                |
|--------------+-----------------------------------+----------------|
| 12.2XNB      | Not Vulnerable                    |                |
|--------------+-----------------------------------+----------------|
| 12.2XO       | Not Vulnerable                    |                |
|--------------+-----------------------------------+----------------|
| 12.2XQ       | Not Vulnerable                    |                |
|--------------+-----------------------------------+----------------|
| 12.2XR       | Not Vulnerable                    |                |
|--------------+-----------------------------------+----------------|
| 12.2XS       | Not Vulnerable                    |                |
|--------------+-----------------------------------+----------------|
| 12.2XT       | Not Vulnerable                    |                |
|--------------+-----------------------------------+----------------|
| 12.2XU       | Not Vulnerable                    |                |
|--------------+-----------------------------------+----------------|
| 12.2XV       | Not Vulnerable                    |                |
|--------------+-----------------------------------+----------------|
| 12.2XW       | Not Vulnerable                    |                |
|--------------+-----------------------------------+----------------|
| 12.2YA       | Not Vulnerable                    |                |
|--------------+-----------------------------------+----------------|
| 12.2YB       | Not Vulnerable                    |                |
|--------------+-----------------------------------+----------------|
| 12.2YC       | Not Vulnerable                    |                |
|--------------+-----------------------------------+----------------|
| 12.2YD       | Not Vulnerable                    |                |
|--------------+-----------------------------------+----------------|
| 12.2YE       | Not Vulnerable                    |                |
|--------------+-----------------------------------+----------------|
| 12.2YF       | Not Vulnerable                    |                |
|--------------+-----------------------------------+----------------|
| 12.2YG       | Not Vulnerable                    |                |
|--------------+-----------------------------------+----------------|
| 12.2YH       | Not Vulnerable                    |                |
|--------------+-----------------------------------+----------------|
| 12.2YJ       | Not Vulnerable                    |                |
|--------------+-----------------------------------+----------------|
| 12.2YK       | Not Vulnerable                    |                |
|--------------+-----------------------------------+----------------|
| 12.2YL       | Not Vulnerable                    |                |
|--------------+-----------------------------------+----------------|
| 12.2YM       | Not Vulnerable                    |                |
|--------------+-----------------------------------+----------------|
| 12.2YN       | Not Vulnerable                    |                |
|--------------+-----------------------------------+----------------|
| 12.2YO       | Not Vulnerable                    |                |
|--------------+-----------------------------------+----------------|
| 12.2YP       | Not Vulnerable                    |                |
|--------------+-----------------------------------+----------------|
| 12.2YQ       | Not Vulnerable                    |                |
|--------------+-----------------------------------+----------------|
| 12.2YR       | Not Vulnerable                    |                |
|--------------+-----------------------------------+----------------|
| 12.2YS       | Not Vulnerable                    |                |
|--------------+-----------------------------------+----------------|
| 12.2YT       | Not Vulnerable                    |                |
|--------------+-----------------------------------+----------------|
| 12.2YU       | Not Vulnerable                    |                |
|--------------+-----------------------------------+----------------|
| 12.2YV       | Not Vulnerable                    |                |
|--------------+-----------------------------------+----------------|
| 12.2YW       | Not Vulnerable                    |                |
|--------------+-----------------------------------+----------------|
| 12.2YX       | Not Vulnerable                    |                |
|--------------+-----------------------------------+----------------|
| 12.2YY       | Not Vulnerable                    |                |
|--------------+-----------------------------------+----------------|
| 12.2YZ       | Not Vulnerable                    |                |
|--------------+-----------------------------------+----------------|
| 12.2ZA       | Not Vulnerable                    |                |
|--------------+-----------------------------------+----------------|
| 12.2ZB       | Not Vulnerable                    |                |
|--------------+-----------------------------------+----------------|
| 12.2ZC       | Not Vulnerable                    |                |
|--------------+-----------------------------------+----------------|
| 12.2ZD       | Not Vulnerable                    |                |
|--------------+-----------------------------------+----------------|
| 12.2ZE       | Not Vulnerable                    |                |
|--------------+-----------------------------------+----------------|
| 12.2ZF       | Not Vulnerable                    |                |
|--------------+-----------------------------------+----------------|
| 12.2ZG       | Not Vulnerable                    |                |
|--------------+-----------------------------------+----------------|
| 12.2ZH       | Not Vulnerable                    |                |
|--------------+-----------------------------------+----------------|
| 12.2ZJ       | Not Vulnerable                    |                |
|--------------+-----------------------------------+----------------|
| 12.2ZL       | Not Vulnerable                    |                |
|--------------+-----------------------------------+----------------|
| 12.2ZP       | Not Vulnerable                    |                |
|--------------+-----------------------------------+----------------|
| 12.2ZU       | Not Vulnerable                    |                |
|--------------+-----------------------------------+----------------|
| 12.2ZX       | Not Vulnerable                    |                |
|--------------+-----------------------------------+----------------|
| 12.2ZY       | Not Vulnerable                    |                |
|--------------+-----------------------------------+----------------|
| 12.2ZYA      | Not Vulnerable                    |                |
|--------------+-----------------------------------+----------------|
|   Affected   |                                   |  Recommended   |
|  12.3-Based  |        First Fixed Release        |    Release     |
|   Releases   |                                   |                |
|-------------------------------------------------------------------|
| There are no affected 12.3 based releases                         |
|-------------------------------------------------------------------|
|   Affected   |                                   |  Recommended   |
|  12.4-Based  |        First Fixed Release        |    Release     |
|   Releases   |                                   |                |
|--------------+-----------------------------------+----------------|
| 12.4         | Not Vulnerable                    |                |
|--------------+-----------------------------------+----------------|
| 12.4JA       | Not Vulnerable                    |                |
|--------------+-----------------------------------+----------------|
| 12.4JK       | Not Vulnerable                    |                |
|--------------+-----------------------------------+----------------|
| 12.4JL       | Not Vulnerable                    |                |
|--------------+-----------------------------------+----------------|
| 12.4JMA      | Not Vulnerable                    |                |
|--------------+-----------------------------------+----------------|
| 12.4JMB      | Not Vulnerable                    |                |
|--------------+-----------------------------------+----------------|
| 12.4JMC      | Not Vulnerable                    |                |
|--------------+-----------------------------------+----------------|
| 12.4JX       | Not Vulnerable                    |                |
|--------------+-----------------------------------+----------------|
| 12.4MD       | Not Vulnerable                    |                |
|--------------+-----------------------------------+----------------|
|              | Note: Releases prior to 12.4(11)  |                |
| 12.4MR       | MR are not vulnerable. First      | 12.4(19)MR     |
|              | fixed in 12.4(16)MR               |                |
|--------------+-----------------------------------+----------------|
|              |                                   | 12.4(15)SW2;   |
| 12.4SW       | 12.4(11)SW3                       | Available on   |
|              |                                   | 28-SEP-08      |
|--------------+-----------------------------------+----------------|
|              | Note: Releases prior to 12.4(11)T |                |
| 12.4T        | are not vulnerable. First fixed   | 12.4(15)T7     |
|              | in 12.4(15)T                      |                |
|--------------+-----------------------------------+----------------|
| 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       | Vulnerable; first fixed in 12.4T  | 12.4(15)T7     |
|--------------+-----------------------------------+----------------|
| 12.4XK       | Not Vulnerable                    |                |
|--------------+-----------------------------------+----------------|
| 12.4XL       | Not Vulnerable                    |                |
|--------------+-----------------------------------+----------------|
| 12.4XM       | Not Vulnerable                    |                |
|--------------+-----------------------------------+----------------|
| 12.4XN       | Not Vulnerable                    |                |
|--------------+-----------------------------------+----------------|
| 12.4XP       | Not Vulnerable                    |                |
|--------------+-----------------------------------+----------------|
| 12.4XQ       | Not Vulnerable                    |                |
|--------------+-----------------------------------+----------------|
| 12.4XT       | Not Vulnerable                    |                |
|--------------+-----------------------------------+----------------|
| 12.4XV       | Vulnerable; contact TAC           |                |
|--------------+-----------------------------------+----------------|
| 12.4XW       | 12.4(11)XW1                       | 12.4(11)XW9    |
|--------------+-----------------------------------+----------------|
| 12.4XY       | Not Vulnerable                    |                |
|--------------+-----------------------------------+----------------|
| 12.4XZ       | Not Vulnerable                    |                |
|--------------+-----------------------------------+----------------|
| 12.4YA       | Not Vulnerable                    |                |
+-------------------------------------------------------------------+

Workarounds
===========

The following workarounds have been identified for this
vulnerability.

Note:  L2TP implementations will need to allow UDP 1701, from trusted
addresses to infrastructure addresses. This does not provide for a
full mitigation as the source addresses may be spoofed.

Note:  L2TPv3 over IP only implementations need to deny all UDP 1701
from anywhere to the infrastructure addresses.

  * Infrastructure Access Control Lists
    Although it is often difficult to block traffic that transits a
    network, it is possible to identify traffic that should never be
    allowed to target infrastructure devices and block that traffic
    at the border of networks. Infrastructure Access Control Lists
    (iACLs) are a network security best practice and should be
    considered as a long-term addition to good network security as
    well as a workaround for these specific vulnerabilities. The iACL
    example below should be included as part of the deployed
    infrastructure access-list which will protect all devices with IP
    addresses in the infrastructure IP address range:



        !--- Permit L2TP UDP 1701 packets from all trusted
        !--- sources destined to infrastructure addresses.
        !--- NOTE: This does not prevent spoofed attacks.
        !---           To be a full mitigation, no trusted source
        !---           addresses should be listed.
        !---           Omit this line if using a L2TPv3 over IP implementation only.


        access-list 150 permit udp TRUSTED_SOURCE_ADDRESSES MASK
           INFRASTRUCTURE_ADDRESSES MASK eq 1701


        !--- Deny L2TP UDP 1701 packets from all
        !--- sources destined to infrastructure addresses.


        access-list 150 deny udp any INFRASTRUCTURE_ADDRESSES MASK eq 1701


        !--- If using a L2TPv3 over IP implementation ensure to allow L2TPv3


        access-list 150 permit 115 <source_ip_address and mask>
           <destination_ip_address and mask>


        !--- Permit/deny all other Layer 3 and Layer 4 traffic in accordance
        !--- with existing security policies and configurations
        !--- Permit all other traffic to transit the device.


        access-list 150 permit ip any any


        !--- Apply access-list to all interfaces (only one example shown)


        interface serial 2/0
        ip access-group 150 in

    The white paper entitled "Protecting Your Core: Infrastructure
    Protection Access Control Lists" presents guidelines and
    recommended deployment techniques for infrastructure protection
    access lists. This white paper can be obtained at the following
    link: 
    http://www.cisco.com/en/US/tech/tk648/tk361/technologies_white_paper09186a00801a1a55.shtml

  * Control Plane Policing
    Control Plane Policing (CoPP) can be used to block L2TP access to
    the device. Cisco IOS software releases 12.0S, 12.2SX, 12.2S,
    12.3T, 12.4, and 12.4T support the CoPP feature. CoPP can be
    configured on a device to protect the management and control
    planes and minimize the risk and effectiveness of direct
    infrastructure attacks by explicitly permitting only authorized
    traffic that is sent to infrastructure devices in accordance with
    existing security policies and configurations. The CoPP example
    below should be included as part of the deployed CoPP which will
    protect all devices with IP addresses in the infrastructure IP
    address range.



        !--- Deny all trusted source L2TP UDP traffic sent to all IP addresses
        !--- configured on all interfaces of the affected device so that it
        !--- will not be policed by the CoPP feature.

        !--- NOTE: This does not prevent spoofed attacks.
        !---           To be a full mitigation, no trusted source
        !---           addresses should be listed.
        !---           Omit this line if using an L2TPv3 over IP implementation only.


        access-list 111 deny udp TRUSTED_SOURCE_ADDRESSES MASK
           INFRASTRUCTURE_ADDRESSES MASK eq 1701


        !--- Permit all L2TP UDP traffic sent to all IP addresses
        !--- configured on all interfaces of the affected device so that it
        !--- will be policed and dropped by the CoPP feature


        access-list 111 permit udp any INFRASTRUCTURE_ADDRESSES MASK eq 1701


        !--- If using an L2TPv3 over IP implementation ensure not to drop L2TPv3


        access-list 111 deny 115 <source_ip_address and mask>
           <destination_ip_address and mask>


        !--- Permit (Police or Drop)/Deny (Allow) all other Layer3 and Layer4
        !--- traffic in accordance with existing security policies and
        !--- configurations for traffic that is authorized to be sent
        !--- to infrastructure devices

        !--- Create a Class-Map for traffic to be policed by
        !--- the CoPP feature



        class-map match-all drop-l2tp-class
        match access-group 111



        !--- Create a Policy-Map that will be applied to the
        !--- Control-Plane of the device.


        policy-map drop-l2tp-traffic
        class drop-l2tp-class
        drop



        !--- Apply the Policy-Map to the 
        !--- Control-Plane of the device


        control-plane

        service-policy input drop-l2tp-traffic

    In the above CoPP example, the access control list entries (ACEs)
    that match the potential exploit packets with the "permit" action
    result in these packets being discarded by the policy-map "drop"
    function, while packets that match the "deny" action (not shown)
    are not affected by the policy-map drop function. Please note
    that the policy-map syntax is different in the 12.2S and 12.0S
    Cisco IOS trains:

        policy-map drop-l2tp-traffic
        class drop-l2tp-class
        police 32000 1500 1500 conform-action drop exceed-action drop

    Additional information on the configuration and use of the CoPP
    feature is available at the following link: 
    http://www.cisco.com/web/about/security/intelligence/coppwp_gs.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: 
http://www.cisco.com/warp/public/707/cisco-amb-20080924-l2tp.shtml

Obtaining Fixed Software
========================

Cisco has released free software updates that address these
vulnerabilities. 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/products/prod_warranties_item09186a008088e31f.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/warp/public/687/Directory/DirTAC.shtml
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 by Cisco through internal testing.

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-20080924-l2tp.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.

Revision History
================

+----------------------------------------+
| Revision |                   | Initial |
| 1.0      | 2008-September-24 | 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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