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             AUSCERT External Security Bulletin Redistribution

                     Citrix Hypervisor Security Update
                             9 September 2021


        AusCERT Security Bulletin Summary

Product:           Citrix Hypervisor
Publisher:         Citrix
Operating System:  Virtualisation
Impact/Access:     Execute Arbitrary Code/Commands -- Existing Account
                   Denial of Service               -- Existing Account
                   Access Confidential Data        -- Existing Account
Resolution:        Patch/Upgrade
CVE Names:         CVE-2021-28701 CVE-2021-28699 CVE-2021-28698
                   CVE-2021-28697 CVE-2021-28696 CVE-2021-28695

Reference:         ESB-2021.3023

Original Bulletin: 

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Citrix Hypervisor Security Update

Reference: CTX325319
Category : High
Created  : 07 September 2021
Modified : 08 September 2021

Applicable Products

  o Citrix Hypervisor

Description of Problem

Several security issues have been discovered in Citrix Hypervisor that,
collectively, may allow privileged code in a guest VM to compromise or crash
the host.
These issues have the following identifiers:
|CVE-ID        |Description|Pre-requisites                                    |
|              |           |Malicious privileged code execution in a guest VM |
|              |           |running on a host with firmware that declares ACPI|
|CVE-2021-28694|Host denial|tables which includes memory regions that are     |
|              |of service |identity mapped for devices that have been        |
|              |           |explicitly assigned, by the host administrator, to|
|              |           |that guest VM in PCI passthrough mode.            |
|CVE-2021-28697|Host       |Malicious privileged code execution in a guest VM |
|              |compromise |that has two or more vCPUs allocated to it        |
|CVE-2021-28698|Host denial|Malicious privileged code execution in a guest VM |
|              |of service |                                                  |
|              |Host       |Malicious privileged code execution in a guest VM |
|CVE-2021-28699|compromise |on a host where the host administrator has        |
|              |           |modified the guest or host grant table limits     |
|CVE-2021-28701|Host       |Malicious privileged code execution in a guest VM |
|              |compromise |that has two or more vCPUs allocated to it        |

All currently supported versions of Citrix Hypervisor are affected by all of
these issues with the exception of CVE-2021-28699 which only affects Citrix
Hypervisor 8.2 LTSR.

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: CTX324257 - https://support.citrix.com/article/
Citrix Hypervisor 7.1 LTSR CU2: CTX324256 - 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

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