[apops] Cisco Security Advisory: Cisco Guard enables Cross Site Scriptin

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  • Subject: [apops] Cisco Security Advisory: Cisco Guard enables Cross Site Scripting
  • From: Cisco Systems Product Security Incident Response Team <psirt at cisco dot com>
  • Date: Wed, 20 Sep 2006 15:00:00 -0000
  • Cc: psirt at cisco dot com
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      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 admin at guard dot example dot com
              admin at guard dot example dot com'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
      http://www.cisco.com/go/psirt 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
      http://www.cisco.com/public/sw-license-agreement.html, or as otherwise
      set forth at Cisco.com Downloads at
      Do not contact either "psirt at cisco dot com" or "security-alert at cisco dot 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
      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: tac at cisco dot 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
      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 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.
        * cust-security-announce at cisco dot com
        * first-teams at first dot org
        * bugtraq at securityfocus dot com
        * vulnwatch at vulnwatch dot org
        * cisco at spot dot colorado dot edu
        * cisco-nsp at puck dot nether dot net
        * full-disclosure at lists.grok dot org dot uk
        * comp.dcom.sys.cisco at newsgate dot cisco dot 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      | 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
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      All contents are Copyright (C) 1992-2006 Cisco Systems, Inc. All rights
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