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             AUSCERT External Security Bulletin Redistribution

                     Citrix Hypervisor Security Update
                             13 November 2020


        AusCERT Security Bulletin Summary

Product:           Citrix Hypervisor
Publisher:         Citrix
Operating System:  Virtualisation
                   Citrix XenServer
Impact/Access:     Access Confidential Data -- Existing Account
Resolution:        Patch/Upgrade
CVE Names:         CVE-2020-8698 CVE-2020-8696 

Reference:         ESB-2020.4033

Original Bulletin: 

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

Citrix Hypervisor Security Update

Reference: CTX285937

Category : Medium

Created  : 12 Nov 2020

Modified : 12 Nov 2020

Applicable Products

  o Citrix Hypervisor
  o XenServer

Description of Problem

A security issue has been identified in Citrix Hypervisor that may allow
privileged code running in a guest VM to infer details of some computations
occurring in other VMs on the host. This may, for example, be used to infer a
secret encryption key used by a web server in a different VM.

A CVE identifier for this issue is not yet available.

|CVE ID               |Description          |Vulnerability Type   |Pre-conditions       |
|TBA                  |Side-channel attack  |CWE-1300             |Malicious code       |
|                     |through exposed      |                     |executing on the     |
|                     |power-monitoring     |                     |host.                |
|                     |interface            |                     |                     |

This issue affects all currently supported versions of Citrix Hypervisor up to
and including Citrix Hypervisor 8.2 LTSR.

In addition, Citrix is aware of two recently disclosed issues affecting Intel
CPUs which are addressed by updated microcode from Intel. Although these are
issues in the underlying hardware platform, Citrix has included this updated
microcode in the hotfixes associated with this bulletin to assist customers who
have not obtained updated firmware from their hardware vendor. These issues
have the following identifiers:

  o CVE-2020-8696
  o CVE-2020-8698

These CPU issues may allow code running in a VM to obtain data being used in
computations within other VMs or other processes within the same VM.

Customers should note that it is necessary to reboot the host for the microcode
update that protects against these Intel CPU issues to take effect. Customers
who are using the Live Patching feature of Citrix Hypervisor and who do not
need the microcode update (either because they are using a CPU from a different
vendor or because they have already updated their host BIOS/UEFI firmware) do
not need to reboot the host after applying the update.

What Customers Should Do

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

Citrix Hypervisor 8.2 LTSR: CTX285172 - https://support.citrix.com/article/

Citrix Hypervisor 8.1: CTX285171 - https://support.citrix.com/article/CTX285171

Citrix XenServer 7.1 LTSR CU2: CTX285170 - https://support.citrix.com/article/

Citrix XenServer 7.0: CTX285169 - https://support.citrix.com/article/CTX285169

Customers who are using the Live Patching feature of Citrix Hypervisor should
consider rebooting the host machine if they are in need of the microcode update
described above.


|Date                      |Change                                            |
|2020-11-12                |Initial Publication                               |

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