Operating System:

[Win]

Published:

18 December 2009

Protect yourself against future threats.

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             AUSCERT External Security Bulletin Redistribution

                               ESB-2009.1662
        Vulnerability in Citrix NetScaler and Citrix Access Gateway
           Enterprise Edition Could Result in Denial of Service
                             18 December 2009

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        AusCERT Security Bulletin Summary
        ---------------------------------

Product:           Access Gateway 7.0 Enterprise Edition
                   Access Gateway 8.0 Enterprise Edition
                   Access Gateway 8.1 Enterprise Edition
                   Access Gateway 9.0 Enterprise Edition
                   Access Gateway 9.1 Enterprise Edition
                   NetScaler Application Delivery Software 7.0
                   NetScaler Application Delivery Software 8.0
                   NetScaler Application Delivery Software 8.1
                   NetScaler Application Delivery Software 9.0
                   NetScaler Application Delivery Software 9.1
                   NetScaler VPX 9.1
Publisher:         Citrix
Operating System:  Windows
Impact/Access:     Denial of Service -- Remote with User Interaction
Resolution:        Patch/Upgrade
CVE Names:         CVE-2008-4609  

Reference:         ESB-2009.1372
                   ESB-2009.1284
                   ESB-2009.1267.2
                   ESB-2009.1263

Original Bulletin: 
   http://support.citrix.com/article/CTX123649

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Vulnerability in Citrix NetScaler and Citrix Access Gateway Enterprise Edition 
Could Result in Denial of Service

Document ID: CTX123649   /   Created On: Dec 16, 2009   /   Updated On: Dec 
16, 2009

Average Rating: not yet rated

Severity: Medium

Description of Problem

A vulnerability has been identified in the NetScaler and Access Gateway 
Enterprise Edition appliance firmware that could result in a limited denial 
of service.

This vulnerability has been assigned the following CVE number(s):

       CVE CVE-2008-4609: The TCP implementation in (1) Linux, (2) platforms 
       based on BSD Unix, (3) Microsoft Windows, (4) Cisco products, and 
       probably other operating systems allows remote attackers to cause a 
       denial of service (connection queue exhaustion) via multiple vectors 
       that manipulate information in the TCP state table, as demonstrated by 
       sockstress.

This vulnerability is present in versions of all versions of Citrix NetScaler 
and Citrix Access Gateway Enterprise Edition up to and including version 9.1.

Mitigating Factors

In order to sustain this denial of service, the attacker would have to maintain 
a high volume of traffic against the target appliance.

What Customers Should Do

This vulnerability has been addressed in versions 9.1.100.3 and 8.1.68.7 of the 
firmware for Citrix NetScaler and Access Gateway Enterprise Edition.

Citrix recommends that customers upgrade their NetScaler and Access Gateway 
Enterprise Edition appliances to these builds of the versions 8.1 and 9.1 
firmware, available at the following locations:

Citrix NetScaler:

http://www.citrix.com/English/ss/downloads/results.asp?productID=21679

Citrix Access Gateway Enterprise Edition: http://www.citrix.com/English/ss/downloads/results.asp?productID=15005&c1=pov1680613

Customers using versions of the NetScaler and Access Gateway Enterprise Edition 
firmware that do not currently have a fix available are recommended to 
implement the following mitigations:

NetScaler/Access Gateway Enterprise Edition 9.0/9.1

- From the NSCLI,

      1. Ensure that the limited persist probe is enabled. The setting is 
         enabled by default, but can be verified using the following command:

      >  show ns tcpparam

      If the probe is not enabled, it can be enabled using the following 
      command:

      >  set tcpparam limitedPersist ENABLED

      2. Modify the client idle timeout value for an existing vServer or 
         service to a lower value, e.g. 60 seconds, using the following 
         command:

      > Set lb vserver <vsvrname> -clttimeout 60

      3. Modify the global client idle timeout value to a lower value, e.g. 
         60 seconds, using the following command:

      For TCP vServers

      > set ns timeout -tcpclient 60

      For HTTP vServers

      > set ns timeout -httpclient 60

NetScaler/Access Gateway Enterprise Edition 8.1

- From the shell,

      1. Ensure that the limited persist probe is enabled. The setting is 
         enabled by default, but can be verified and enabled using the 
         following command:

      bash#  nsapimgr -ys limited_persistprobe=1

- From the NSCLI,

      1. Modify the client idle timeout value for an existing vServer or 
         service to a lower value, e.g. 60 seconds, using the following 
         command:

      > Set lb vserver <vsvrname> -clttimeout 60

      2. Modify the global client idle timeout value to a lower value, e.g. 60 
         seconds, using the following command:

      > set ns timeout -client 60

NetScaler/Access Gateway Enterprise Edition 8.0

- From the shell,

      1. Ensure that the limited persist probe is enabled. The setting is 
         enabled by default, but can be verified and enabled using the 
         following command:

      bash#  nsapimgr -ys limited_persistprobe=1

- From the NSCLI,

      2. Modify the client idle timeout value for an existing vServer or 
         service to a lower value, e.g. 60 seconds, using the following 
         command:

      > Set lb vserver <vsvrname> -clttimeout 60

      3. Modify the global client idle timeout value to a lower value, e.g. 60 
         seconds, using the following command:

      > set ns idletimeout tcpclt 60

NetScaler 7.0

- From the shell,

      1. Ensure that the limited persist probe is enabled. The setting is 
         enabled by default, but can be verified and enabled using the 
         following command:

      bash#  nsapimgr -ys limited_persistprobe=1

- From the NSCLI,

      2. Modify the client idle timeout value for an existing vServer or 
         service to a lower value, e.g. 60 seconds, using the following 
         command:

      > Set lb vserver <vsvrname> -clttimeout 60

- From the shell,

      3. Modify the global client idle timeout value to a lower value, e.g. 60 
         seconds, using the following command:

      bash# nsapimgr ys clientconnidletimeout=6000

            Note that this timeout value increments in 10ms intervals.

Citrix recommends that thorough testing is carried out on any NetScaler or 
Access Gateway Enterprise Edition appliance that has been modified in this way 
prior to deployment in a live environment.

What Citrix Is Doing

Citrix is notifying customers and channel partners about this potential 
security issue. This article is also available from the Citrix Knowledge Center 
at http://support.citrix.com/.

Obtaining Support on This Issue

If you require technical assistance with this issue, please contact Citrix 
Technical Support. Contact details for Citrix Technical Support are available 
at http://www.citrix.com/site/ss/supportContacts.asp.

Reporting Security Vulnerabilities to Citrix

Citrix welcomes input regarding the security of its products and considers any 
and all potential vulnerabilities seriously. If you would like to report a 
security issue to Citrix, please compose an e-mail to secure@citrix.com stating 
the exact version of the product in which the vulnerability was found and the 
steps needed to reproduce the vulnerability

This document applies to:

    * Access Gateway 7.0 Enterprise Edition
    * Access Gateway 8.0 Enterprise Edition
    * Access Gateway 8.1 Enterprise Edition
    * Access Gateway 9.0 Enterprise Edition
    * Access Gateway 9.1 Enterprise Edition
    * NetScaler Application Delivery Software 7.0
    * NetScaler Application Delivery Software 8.0
    * NetScaler Application Delivery Software 8.1
    * NetScaler Application Delivery Software 9.0
    * NetScaler Application Delivery Software 9.1
    * NetScaler VPX 9.1

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