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             AUSCERT External Security Bulletin Redistribution

       Denial of service vulnerabilities patched in Citrix XenServer
                               29 June 2018


        AusCERT Security Bulletin Summary

Product:           Citrix XenServer
Publisher:         Citrix
Operating System:  Virtualisation
Impact/Access:     Denial of Service -- Existing Account
Resolution:        Patch/Upgrade
CVE Names:         CVE-2018-12893 CVE-2018-12891 

Original Bulletin: 

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Citrix XenServer Multiple Security Updates

Security Bulletin | Priority: High
Created: 28 Jun 2018 | Modified: 28 Jun 2018

Applicable Products

  * XenServer 7.5
  * XenServer 7.4
  * XenServer 7.3
  * XenServer 7.1 LTSR Cumulative Update 1
  * XenServer 7.0

Description of Problem

Two issues have been identified within Citrix XenServer, which could, if
exploited, allow unprivileged code in a PV guest VM to cause the host to crash
or become unresponsive.

These vulnerabilities affect all currently supported versions of Citrix
XenServer up to and including Citrix XenServer 7.5.

The following vulnerabilities have been addressed:

  * CVE-2018-12893: (High) x86: #DB exception safety check can be triggered by
    a guest
  * CVE-2018-12891: (Medium) preemption checks bypassed in x86 PV MM handling

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What Customers Should Do

Hotfixes have been released to address these issues. Citrix recommends that
affected customers install these hotfixes as soon as possible. The hotfixes can
be downloaded from the following locations:

  * Citrix XenServer 7.5: CTX236153 ? https://support.citrix.com/article/
  * Citrix XenServer 7.4: CTX236152 ? https://support.citrix.com/article/
  * Citrix XenServer 7.3: CTX236151 ? https://support.citrix.com/article/
  * Citrix XenServer 7.1 LTSR CU1: CTX236150 ? https://support.citrix.com/
  * Citrix XenServer 7.0: CTX236149 ? https://support.citrix.com/article/

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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                                                |
|28th June 2018        |Initial issue                                         |
|28th June 2018        |Typo - Mark bulletin as High severity                 |
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