Hash: SHA256

             AUSCERT External Security Bulletin Redistribution

                     Citrix XenServer Security Update
                             14 November 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-2018-18883  

Original Bulletin: 

Revision History:  November 14 2018: Update with assigned CVE number 
                   October  29 2018: Initial Release

- --------------------------BEGIN INCLUDED TEXT--------------------


Citrix XenServer Security Update

Security Bulletin
Priority: Medium
Created: 26 Oct 2018
Modified: 13 Nov 2018

Applicable Products

  * XenServer 7.6
  * XenServer 7.5
  * 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: 

  * Citrix XenServer 7.6
  * Citrix XenServer 7.5
  * Citrix XenServer 7.1 LTSR CU1 

The following vulnerabilities have been addressed: 

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

Mitigating Factors

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

- -------------------------------------------------------------------------------

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.

- -------------------------------------------------------------------------------


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

- --------------------------END INCLUDED TEXT--------------------

You have received this e-mail bulletin as a result of your organisation's
registration with AusCERT. The mailing list you are subscribed to is
maintained within your organisation, so if you do not wish to continue
receiving these bulletins you should contact your local IT manager. If
you do not know who that is, please send an email to auscert@auscert.org.au
and we will forward your request to the appropriate person.

NOTE: Third Party Rights
This security bulletin is provided as a service to AusCERT's members.  As
AusCERT did not write the document quoted above, AusCERT has had no control
over its content. The decision to follow or act on information or advice
contained in this security bulletin is the responsibility of each user or
organisation, and should be considered in accordance with your organisation's
site policies and procedures. AusCERT takes no responsibility for consequences
which may arise from following or acting on information or advice contained in
this security bulletin.

NOTE: This is only the original release of the security bulletin.  It may
not be updated when updates to the original are made.  If downloading at
a later date, it is recommended that the bulletin is retrieved directly
from the author's website to ensure that the information is still current.

Contact information for the authors of the original document is included
in the Security Bulletin above.  If you have any questions or need further
information, please contact them directly.

Previous advisories and external security bulletins can be retrieved from:


Australian Computer Emergency Response Team
The University of Queensland
Qld 4072

Internet Email: auscert@auscert.org.au
Facsimile:      (07) 3365 7031
Telephone:      (07) 3365 4417 (International: +61 7 3365 4417)
                AusCERT personnel answer during Queensland business hours
                which are GMT+10:00 (AEST).
                On call after hours for member emergencies only.
Comment: http://www.auscert.org.au/render.html?it=1967