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Denial of Service Vulnerability in Cisco Wide Area Application Services (WAAS) Software



Cisco Security Advisory: Denial of Service Vulnerability in Cisco Wide Area Application Services (WAAS) Software
Cisco Security Advisory: Denial of Service Vulnerability in Cisco Wide Area Application Services (WAAS) Software



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Cisco Security Advisory: Denial of Service Vulnerability in Cisco Wide
Area Application Services (WAAS) Software

Advisory ID: cisco-sa-20070718-waas

http://www.cisco.com/warp/public/707/cisco-sa-20070718-waas.shtml 

Revision 1.0

For Public Release 2007 July 18 1600 UTC (GMT)

+----------------------------------------------------------------------

Summary
======
The Cisco Wide Area Application Services (WAAS) software contains a
denial of service (DoS) vulnerability that may cause some devices
that run WAAS software (WAE appliance and NM-WAE-502 module) to stop
processing all types of traffic, including data traffic and management
traffic. This condition may occur if a device running WAAS software is
configured for Edge Services, which utilizes Common Internet File System
(CIFS) optimization and receives a flood of TCP SYN packets on port 139
or 445.

Cisco has made free software available to address this vulnerability for
affected customers. Workarounds are available to mitigate the effects of
this vulnerability.

This advisory is posted at
http://www.cisco.com/warp/public/707/cisco-sa-20070718-waas.shtml. 

Affected Products
================
Vulnerable Products
+------------------

The vulnerability described in this document applies to both the
WAE appliance and the NM-WAE-502 network module with Edge Services
configured, which use CIFS optimization. Edge Services and CIFS
optimization are disabled by default. CIFS functionality is only
available once Edge Services are manually configured from the WAAS
Central Manager. Only WAAS software versions 4.0.7 and 4.0.9 are
affected by this vulnerability.

In order to determine whether Edge Services are configured and to
display the WAAS software version information, use the WAAS Central
Manager GUI. The "show version" EXEC command from the CLI will also
display the WAAS software version information.

Determine whether Edge Services are configured and display the WAAS
software version information by following the steps below.

 1. Log on to WAAS Central Manager.
 2. Select the "Devices" tab.
 3. Look under the Services column. "Edge" will denote if Edge
    Services are configured.
 4. Look under the Software Version column. The software version for
    each device is identified.

The example below shows the output of the "show version" command from a
WAE appliance CLI. In this example, the WAE is running version 4.0.9.

    CE-115-16#show version
    Cisco Wide Area Application Services Software (WAAS)
    Copyright (c) 1999-2007 by Cisco Systems, Inc.
    Cisco Wide Area Application Services Software Release 4.0.9 (build b10 Apr  6 2007)
    Version: fe611-4.0.9.10

    Compiled 15:26:06 Apr  6 2007 by cnbuild

    System was restarted on Sat Jun 16 05:03:41 2007.
    The system has been up for 33 minutes, 40 seconds.

    CE-115-16#

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

No other Cisco products or versions of WAAS software that are not
explicitly identified in this advisory are currently known to be
affected by this vulnerability.

WAE appliances and NM-WAE-502 modules that are not configured to
provide Edge Services performing CIFS optimization are not affected.
The NM-WAE-302 is not susceptible to this vulnerability as it cannot be
configured for CIFS optimization.

Details
======
The Cisco Wide Area Application Services solution uses a combination of
application acceleration and WAN optimization techniques to mitigate
application and transport latency. WAAS software is utilized on the Wide
Area Application Engine appliance and the Wide Area Application Services
Network Module that are incorporated in the solution.

A DoS vulnerability exists in some versions of WAAS software that may
cause some devices that run WAAS software (WAE appliance and
NM-WAE-502 module) to stop processing all types of traffic, including
traffic going through the device (data traffic) and traffic
terminating on the device (management traffic). If the WAAS device
has Edge Services, which uses CIFS optimization configured, and
receives a flood of TCP SYN packets on ports 139 or 445, this
vulnerability may be triggered, resulting in a DoS condition. Ports
139 and 445 are utilized by the CIFS functionality of the WAAS
software. This condition may result from network traffic that is sent
directly to the WAAS platform, or by automated systems such as
hostscanners, portscanners, or network worms.

This vulnerability is documented in Cisco Bug ID CSCsi58809.

Vulnerability Scoring Details
+----------------------------

Cisco is providing 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 1.0.

Cisco will provide a base and temporal score. Customers can then
compute environmental scores to assist in determining the impact of the
vulnerability in individual networks.

Cisco PSIRT will set the bias in all cases to normal. Customers
are encouraged to apply the bias parameter when determining the
environmental impact of a particular vulnerability.

CVSS is a standards-based scoring method that conveys vulnerability
severity and helps determine urgency and priority of response.

Cisco has provided an FAQ to answer additional questions regarding
CVSS at
http://www.cisco.com/web/about/security/intelligence/cvss-qandas.html. 

Cisco has also provided a CVSS calculator to help compute the
environmental impact for individual networks at
http://intellishield.cisco.com/security/alertmanager/cvss. 

CSCsi58809: SYN flood causes device to become unresponsive

CVSS Base Score: 3.3
    Access Vector: Remote
    Access Complexity: Low
    Authentication: Not Required
    Confidentiality Impact: None
    Integrity Impact: None
    Availability Impact: Complete
    Impact Bias: Normal

CVSS Temporal Score: 2.7
    Exploitability: Functional
    Remediation Level: Official Fix
    Report Confidence: Confirmed

Impact
=====
Successful exploitation of the vulnerability described in this document
may allow a remote host to cause a device that is running an affected
version of the WAAS software with Edge Services using CIFS optimization
configured to enter into an unresponsive state. During this unresponsive
state, no services are provided, including management access to the
device. Recovery of the system from this unresponsive state can only
be accomplished by resetting or power cycling the affected device. The
following process can be used to remotely recover the NM-WAE-502.

Remote Recovery of the NM-WAE-502
+--------------------------------

Log in to the router and issue the following command from IOS CLI to
reboot the NM-WAE-502:

    Router# service-module integrated-Service-Engine / reset

Software Version 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.

This vulnerability is fixed in version 4.0.11 of the Cisco WAAS
software. WAAS public software releases have version numbers that end in
odd numbers and can be downloaded from the following URL:

http://www.cisco.com/pcgi-bin/tablebuild.pl/waas40?psrtdcat20e2 

Workarounds
==========
If the device that is running WAAS software does not need to provide
Edge Services, then disabling Edge Services is a viable workaround. When
the Edge Services are turned off, CIFS clients may not benefit from the
response time reduction that is associated with the operation of the
CIFS cache, preposition and other CIFS latency optimizations. However,
other Layer 4 optimizations will continue to apply according to the
application policy settings.

In order to disable Edge Services, which includes the CIFS accelerator
and CIFS auto discovery features, follow the steps below.

 1. Log in to WAAS Central Manager.
 2. Select the "Devices" tab.
 3. Select the "Devices" category (or "Device Groups" if using
    multiple devices in groups).
 4. Choose target device or group.
 5. Choose "File Services" located in the left column under
    "Contents."
 6. Choose "Edge configuration" located under "File Services."
 7. Uncheck "Enable Edge Server."
 8. Click Submit.

Transit ACLs (tACL)
+------------------

Filters that block access to TCP ports 139 and 445 packets should be
deployed at the network edge as part of a transit access list, which
will protect the router where the filter is configured as well as
other devices behind it. Filters should also be deployed in front of
vulnerable network devices so that TCP ports 139 and 445 packets are
only allowed from trusted CIFS Clients to trusted CIFS Servers.

Further information about transit ACLs is available in the white
paper "Transit Access Control Lists: Filtering at Your Edge" at
the following link:
http://www.cisco.com/en/US/tech/tk648/tk361/technologies_white_paper09186a00801afc76.shtml 

Further information about configuring ACLs on the WAAS client
is in the "Creating and Managing IP Access Control Lists for
WAAS Devices" chapter of the WAAS Configuration Guide at the
following link:
http://www.cisco.com/en/US/products/ps6870/products_configuration_guide_chapter09186a00807bb6b9.html 

Additional mitigations that can be deployed on Cisco devices within
the network are discussed in the Cisco Applied Intelligence companion
document for this advisory available at the following link:
http://www.cisco.com/warp/public/707/cisco-air-20070718-waas.shtml 

Obtaining Fixed Software
=======================
Cisco will make free software available to address this vulnerability
for affected customers. This advisory will be updated as fixed software
becomes available. Prior to deploying software, customers should consult
their maintenance provider or check the software for feature set
compatibility and known issues specific to their environment.

Customers may only install and expect support for the feature
sets they have purchased. By installing, downloading, accessing
or otherwise using such software upgrades, customers agree to
be bound by the terms of Cisco's software license terms found
at http://www.cisco.com/public/sw-license-agreement.html, 
or as otherwise set forth at Cisco.com Downloads at
http://www.cisco.com/public/sw-center/sw-usingswc.shtml. 

Do not contact either "psirt@cisco.com" or "security-alert@cisco.com" 
for software upgrades.

Customers with Service Contracts
+-------------------------------

Customers with contracts should obtain upgraded software through their
regular update channels. For most customers, this means that upgrades
should be obtained through the Software Center on Cisco's worldwide
website at http://www.cisco.com. 

Customers using Third Party Support Organizations
+------------------------------------------------

Customers whose Cisco products are provided or maintained through prior
or existing agreement with third-party support organizations such as
Cisco Partners, authorized resellers, or service providers should
contact that support organization for guidance and assistance with the
appropriate course of action in regards to this advisory.

The effectiveness of any workaround or fix is dependent on specific
customer situations such as product mix, network topology, traffic
behavior, and organizational mission. Due to the variety of affected
products and releases, customers should consult with their service
provider or support organization to ensure any applied workaround or fix
is the most appropriate for use in the intended network before it is
deployed.

Customers without Service Contracts
+----------------------------------

Customers who purchase direct from Cisco but who do not hold a Cisco
service contract and customers who purchase through third-party vendors
but are unsuccessful at obtaining fixed software through their point
of sale should obtain their upgrades by contacting the Cisco Technical
Assistance Center (TAC). TAC contacts are as follows.

  * +1 800 553 2447 (toll free from within North America)
  * +1 408 526 7209 (toll call from anywhere in the world)
* e-mail: tac@cisco.com 

Have your product serial number available and give the URL of this
notice as evidence of your entitlement to a free upgrade. Free upgrades
for non-contract customers must be requested through the TAC.

Refer to http://www.cisco.com/warp/public/687/Directory/DirTAC.shtml 
for additional TAC contact information, including special localized
telephone numbers and instructions and e-mail addresses for use in
various languages.

Exploitation and Public Announcements
====================================
The Cisco PSIRT is not aware of any public announcements or malicious
use of the vulnerability described in this advisory.

This vulnerability was discovered during the resolution of customer
support cases.

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-20070718-waas.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 1.0  | 2007-July-18  | Initial public release    |
+-----------------------------------------------------------+

Cisco Security Procedures
========================
Complete information on reporting security vulnerabilities in
Cisco products, obtaining assistance with security incidents, and
registering to receive security information from Cisco, is available
on Cisco's worldwide website at
http://www.cisco.com/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. 

+--------------------------------------------------------------------
All contents are Copyright(C) 2006-2007 Cisco Systems, Inc.
All rights reserved.
+--------------------------------------------------------------------

Updated: Jul 18, 2007                              Document ID: 92020

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