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             AUSCERT External Security Bulletin Redistribution

       Citrix patches speculative execution variant 4a in XenServer
                                28 May 2018


        AusCERT Security Bulletin Summary

Product:           Citrix XenServer
Publisher:         Citrix
Operating System:  Windows
Impact/Access:     Access Privileged Data -- Existing Account
Resolution:        Patch/Upgrade
CVE Names:         CVE-2018-3639  

Original Bulletin: 

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Citrix XenServer Security Update for CVE-2018-3639

Security Bulletin | Created: 22 May 2018 | Modified: 22 May 2018

Applicable Products

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

Description of Problem

CVE-2018-3639 Speculative Store Bypass Disable is an issue that may affect
third-party software that runs in guest VMs on Citrix XenServer.  This is not
an issue caused by Citrix XenServer and Citrix is unaware of any means of
exploiting this issue against XenServer itself.
Third-party software can mitigate this issue by restructuring of the code; for
Intel CPUs, third-party software may instead choose to mitigate this issue by
selectively enabling and disabling a CPU feature known as memory
disambiguation.  This requires both new host firmware and the new functionality
of that firmware to be exposed to guest VMs.  To expose this firmware
functionality, Citrix is releasing hotfixes for supported versions of Citrix
XenServer 7.x.

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What Customers Should Do

Customers wishing to expose the new host firmware functionality to their guest
VMs should install both the Citrix XenServer hotfixes and updated host firmware
or BIOS code.  The locations of the Citrix XenServer hotfixes are listed below;
Citrix recommends following your hardware supplier's guidance for firmware

Citrix XenServer 7.4: CTX235133 - https://support.citrix.com/article/CTX235133

Citrix XenServer 7.3: CTX235132 - https://support.citrix.com/article/CTX235132

Citrix XenServer 7.1 LTSR CU1: CTX235131 - https://support.citrix.com/article/

Citrix XenServer 7.0: CTX235130 - https://support.citrix.com/article/CTX235130

Note that, in line with previous issues that were not vulnerabilities in Citrix
XenServer, mitigations are not available for versions 6.x of Citrix XenServer.

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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                                       |
|22nd May 2018                  |Initial Publication                          |

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