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             AUSCERT External Security Bulletin Redistribution

                CTX239100: Citrix XenServer Security Update
                              2 November 2018


        AusCERT Security Bulletin Summary

Product:           Citrix XenServer
Publisher:         Citrix
Operating System:  Xen
Impact/Access:     Denial of Service -- Existing Account
Resolution:        Patch/Upgrade
CVE Names:         CVE-2018-18883  

Original Bulletin: 

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Citrix XenServer Security Update

Security Bulletin 

Severity: Medium

Created: 26 Oct 2018

Modified: 01 Nov 2018

Applicable Products

  o XenServer 7.6
  o XenServer 7.5
  o XenServer 7.1 LTSR Cumulative Update 1

Description of Problem

A security issue has been identified in Citrix XenServer that may allow a
malicious administrator of an HVM guest VM to crash the host.

This issue affects the following versions of Citrix XenServer:

  o Citrix XenServer 7.6
  o Citrix XenServer 7.5
  o Citrix XenServer 7.1 LTSR CU1

The following vulnerabilities have been addressed:

  o CVE-2018-18883: Nested VT-x usable even when disabled

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Mitigating Factors

Customers with only PV guests are not affected by this issue.

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What Customers Should Do

Hotfixes have been released to address this issue. Citrix recommends that
affected customers install these hotfixes as their patching schedule permits.
The hotfixes can be downloaded from the following locations:

Citrix XenServer 7.6: CTX239128 - https://support.citrix.com/article/CTX239128
Citrix XenServer 7.5: CTX239127 - https://support.citrix.com/article/CTX239127
Citrix XenServer 7.1 LTSR CU1: CTX239126 - https://support.citrix.com/article/

Customers who are using the LivePatching feature of Citrix XenServer will not
need to reboot servers to apply this hotfix if those servers were previously
fully patched.

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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/.

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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  https://www.citrix.com/support/open-a-support-case.html.

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Reporting Security Vulnerabilities

Citrix welcomes input regarding the security of its products and considers any
and all potential vulnerabilities seriously. For guidance on how to report
security-related issues to Citrix, please see the following document: CTX081743
- - Reporting Security Issues to Citrix

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|Date                                  |Change                                |
|26th October 2018                     |Initial Issue                         |
|1st November 2018                     |Update with assigned CVE number       |

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