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Category:   Device (Intrusion Detection)  >   Cisco Guard Vendors:   Cisco
Cisco Guard Input Validation Flaw in Anti-Spoofing Feature Permits Cross-Site Scripting Attacks
SecurityTracker Alert ID:  1016890
SecurityTracker URL:
CVE Reference:   CVE-2006-4909   (Links to External Site)
Updated:  Jun 3 2008
Original Entry Date:  Sep 20 2006
Impact:   Disclosure of authentication information, Disclosure of user information, Execution of arbitrary code via network, Modification of user information
Fix Available:  Yes  Vendor Confirmed:  Yes  
Version(s): prior to 5.1(6)
Description:   A vulnerability was reported in Cisco Guard. A remote user can conduct cross-site scripting attacks.

When the anit-spoofing feature is enabled, the device does not properly filter HTML code from user-supplied input. A remote user can create a specially crafted URL that, when loaded by a target user, will cause arbitrary scripting code to be executed by the target user's browser. The code will originate from an arbitrary site protected by the device. As a result, the code will be able to access the target user's cookies (including authentication cookies), if any, associated with the site, access data recently submitted by the target user via web form to the site, or take actions on the site acting as the target user.

A remote user can exploit this even if the protected website does not contain a cross-site scripting vulnerability if the site returns a meta refresh in response to an invalid link where the site does not validate the link data.

The following products are affected:

* Cisco Guard Appliance (Software Version 3.X)
* Cisco Guard Blade (Software Version 4.X)
* Cisco Guard Appliance [Software Version 5.0(3)]
* Cisco Guard Appliance [Software Version 5.1(5)]

Cisco has assigned bug ID CSCsf01438 to this vulnerability.

A customer reported this vulnerability to Cisco.

Impact:   A remote user can access the target user's cookies (including authentication cookies), if any, associated with arbitrary sites protected by the device, access data recently submitted by the target user via web form to the site, or take actions on the site acting as the target user.
Solution:   Cisco has issued a fixed version (5.1(6)) of the Cisco Anomaly Guard code.

The Cisco advisory is available at:

Vendor URL: (Links to External Site)
Cause:   Input validation error

Message History:   None.

 Source Message Contents

Subject:  Cisco Security Advisory: Cisco Guard enables Cross Site Scripting

Hash: SHA1

Cisco Security Advisory: Cisco Guard Enables Cross Site Scripting

Advisory ID: cisco-sa-20060920-guardxss

Revision 1.0

For Public Release 2006 September 20 1600 UTC (GMT)



    Affected Products
    Software Version and Fixes
    Obtaining Fixed Software
    Exploitation and Public Announcements
    Status of this Notice: FINAL
    Revision History
    Cisco Security Procedures



A vulnerability in the Cisco Guard may enable an attacker to send a
web browser client to a malicious website with the use of Cross Site
Scripting (XSS) when the Guard is providing anti-spoofing services
between the web browser client and a webserver. The attacker may
exploit this by providing a malicious URL for the web browser client
to go to, often in email, followed off of a malicious website, or in
an instant message. This issue may occur even if the protected
website does not allow XSS. A software upgrade is required to fix
this vulnerability. There is a workaround available to mitigate the
effects of the vulnerability.

This advisory is available at

Affected Products

The Cisco Guard is the only affected product. Details are available

Vulnerable Products

The following Cisco products are vulnerable.

  * Cisco Guard Appliance (Software Version 3.X)
  * Cisco Guard Blade (Software Version 4.X)
  * Cisco Guard Appliance [Software Version 5.0(3)]
  * Cisco Guard Appliance [Software Version 5.1(5)]

Products Confirmed Not Vulnerable

No other Cisco products have been found to be vulnerable.

There are three ways to determine the software version that your
Cisco Guard DDoS mitigation appliance is running. An example of each
method is shown here:

  * Virtual terminal or local serial console connection
    To determine the software version number through the local serial
    console use a serial cable and a terminal emulation program to
    connect to the appliance. Once you are connected, press the Enter
    key of your terminal and the Guard will present, without even
    logging in, the version of the software running on the devices:
        Cisco Guard Version 3.1(0.12)
        GUARD login:
    In this example the Cisco Guard is running software version 3.1.
    For a virtual terminal, the procedure is the same except that no
    serial cable or terminal emulation program is needed (a standard
    keyboard and monitor are directly connected to the appliance).
  * Remote Secure Shell (SSH) connection
    To obtain the software version number through a SSH session, use
    a SSH client to log in to the Cisco Guard and issue the show
    version command-line interface (CLI) command.
        prompt$ ssh's password:
        Last login: Wed Nov 24 22:45:53 on ttyS0
        admin@GUARD#show version
        Copyright (c) 2000-2004 Cisco Systems, Inc. All rights reserved.
        Software License Agreement
        Cisco Anomaly Guard
        Release: 3.1(0.12)
        Date:    2004/10/27 19:58:14
        GUARD uptime is 3 weeks, 3 days, 17 hours, 53 minutes
        System Serial Number:  XXXXXXX
    In this example, the Cisco Traffic Anomaly Guard is running
    software version 3.1.
  * Remote secure web session
    To obtain the software version that Cisco Guard is running
    through a secure web interface, open the URL 
    https://IP address of your Guard/ in a web browser, log in, 
    and then click on the About link located on the top right section
    of the browser window.


The Cisco Guard DDoS Mitigation Appliance is a distributed
denial-of-service (DDoS) protection system. Malicious DOS traffic is
identified with a Cisco Detector and diverted to the Guard for attack
mitigation. Under normal circumstances, the Guard plays no role in
valid traffic; it is specifically designed to deal with large volumes
of invalid traffic.

Cross Site Scripting (XSS) is an attack where a user follows a link
that contains an embedded script. The link often looks valid, and
sends the user to a valid site. The recipient website does not
contain the link that is sent and sends a meta-refresh back to the
user without validating the data it is sent. When receiving the
meta-refresh, the web browser interprets the script as an instruction
from the website and the script is executed on the user's machine .

In this case, when the anti-spoofing feature is enabled, all diverted
HTTP traffic is inspected and then a meta-refresh is sent to the
client containing the original request. If the original URL contains
a script and a specific character sequence, the meta-refresh from the
Guard will allow the client machine to execute the malicious script.

Several conditions are required to be true in order for the malicious
script to be processed:

  * The client user must follow a URL with a specifically formatted,
    embedded script to a site protected by the Guard.
  * The Guard must be running active basic protection, going through
    basic/redirect protection.
  * The specially crafted http request must be diverted through the
    Guard, and processed by the Guard.

Only if all of the above conditions are met will the client receive
the meta-refresh and process the embedded script.

This vulnerability is being tracked by bug ID CSCsf01438. 


Successful exploitation of the vulnerability may result in malicious
executable code being run by an individual user using a web browser.

Software Version and Fixes

When considering software upgrades, also consult and any subsequent advisories to
determine exposure and a complete upgrade solution.

This vulnerability is fixed in version 5.1(6) of the Cisco Anomaly
Guard code.

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.


Changing the basic/redirect protection to basic/safe-reset protects
the client from executing the embedded script. Instead of providing a
layer seven http meta-refresh to the browser with the malicious URL
intact, the Guard provides a layer three TCP-RST to end the
connection. This can cause minor compatability issues, as some
firewalls do not forward the TCP-RST. However, this method protects
users from any XSS attacks until the Guard can be upgraded to a fixed
version of code.

To turn off basic/redirect and configure basic/safe-reset, please
follow the example below.

 1. Show the zone.
        user@GUARD#show zone test
         **** USER FILTERS ****
        Row Source IP Source Mask     Proto DPort Frg Action Rate Burst Units RxRate(pps)
        10  * 6     80    no  basic/redirect
        user@GUARD#config t
        user@GUARD-conf#zone test
        user@GUARD-conf-zone-test# no user-filter 10
 2. Configure basic/safe-reset dynamic filter.
        user@GUARD-conf-zone-test#user-filter 10 basic/safe-reset * 6 80
 3. Show that the filter is applied.
        user@GUARD#show zone test
         **** USER FILTERS ****
        Row Source IP Source Mask     Proto DPort Frg Action Rate Burst Units RxRate(pps)
        10  * 6     80    no  basic/safe-reset
For more information, please refer to the configuration guide:

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

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, or as otherwise
set forth at Downloads at

Do not contact either "" or ""
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
for the appliance or 
for the 7600 module.

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 get 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:

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

Refer to
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 reported to Cisco by a customer.

Status of this Notice: FINAL


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.


This advisory is posted on Cisco's worldwide website at:

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.


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      | 2006-September-20 | 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
This includes instructions for press inquiries regarding Cisco
security notices.  All Cisco security advisories are available at

- ---------------------------------------------------------------------
All contents are Copyright (C) 1992-2006 Cisco Systems, Inc. All rights
Version: GnuPG v1.4.2.2 (SunOS)



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