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             AUSCERT External Security Bulletin Redistribution

                     Citrix Hypervisor Security Update
                               10 June 2021


        AusCERT Security Bulletin Summary

Product:           Hypervisor
Publisher:         Citrix
Operating System:  Virtualisation
Impact/Access:     Denial of Service        -- Existing Account
                   Access Confidential Data -- Existing Account
Resolution:        Patch/Upgrade
CVE Names:         CVE-2021-28692 CVE-2021-27379 CVE-2021-26313
                   CVE-2021-0089 CVE-2020-15565 

Reference:         ESB-2021.1314

Original Bulletin: 

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Citrix Hypervisor Security Update

Reference: CTX316324
Category : Medium
Created  : 09 June 2021
Modified : 09 June 2021

Applicable Products

  o Citrix Hypervisor

Description of Problem

Several security issues have been identified that affect Citrix Hypervisor:

Two issues, each of which may each allow privileged code in a guest VM to cause
the host to crash or become unresponsive. These two issues only affect systems
where the malicious guest VM has a physical PCI device passed through to it by
the host administrator.

These issues have the following identifiers:

  o CVE-2021-27379
  o CVE-2021-28692

A further issue that affects underlying CPU hardware. Although this is not an
issue in the Citrix Hypervisor product itself, Citrix is releasing hotfixes
that also address this CPU issue. This issue is of a type known as "speculative
execution attacks" and may allow malicious code running on a CPU to infer the
value of registers or memory belonging to other processes running on that CPU.

This issue has the following identifiers:

  o CVE-2021-0089 (Intel CPUs)/CVE-2021-26313 (AMD CPUs)

|CVE ID        |Description                  |Pre-conditions                  |
|              |                             |malicious guest VM must have a  |
|              |privileged code in a guest VM|physical PCI device passed      |
|CVE-2021-27379|may cause the host to crash  |through by the host             |
|              |or become unresponsive       |administrator and the attacker  |
|              |                             |must be able to execute         |
|              |                             |privileged code                 |
|              |                             |malicious guest VM must have a  |
|              |privileged code in a guest VM|physical PCI device passed      |
|CVE-2021-28692|may cause the host to crash  |through by the host             |
|              |or become unresponsive       |administrator and the attacker  |
|              |                             |must be able to execute         |
|              |                             |privileged code                 |
|              |malicious code running on a  |                                |
|CVE-2021-0089/|CPU could infer the value of |Ability to execute code in a    |
|CVE-2021-26313|registers or memory belonging|guest VM                        |
|              |to other processes running on|                                |
|              |that CPU                     |                                |

Mitigating Factors

Customers who have not assigned a PCI device to a guest VM are not affected by
CVE-2021-27379 or CVE-2021-28692

What Customers Should Do

Citrix has released hotfixes to address these issues. 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: CTX313807 - https://support.citrix.com/article/
Citrix XenServer 7.1 LTSR CU2: CTX313806 - https://support.citrix.com/article/

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 https://support.citrix.com/ .

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/ .

Reporting Security Vulnerabilities to Citrix

Citrix welcomes input regarding the security of its products and considers any
and all potential vulnerabilities seriously. For details on our vulnerability
response process and guidance on how to report security-related issues to
Citrix, please see the following webpage: https://www.citrix.com/about/
trust-center/vulnerability-process.html .


This document is provided on an "as is" basis and does not imply any kind of
guarantee or warranty, including the warranties of merchantability or fitness
for a particular use. Your use of the information on the document is at your
own risk. Citrix reserves the right to change or update this document at any


Date       Change
2021-06-09 Initial Publication

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