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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)

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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_paper09186a00...

* 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.htm..., 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 ============================

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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 ==========================

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