Citrix Hypervisor Security Update

Description of Problem

Two security issues have been identified in Citrix Hypervisor (formerly Citrix XenServer) that may allow privileged code in a guest VM to cause the host to crash or become unresponsive.

These issues affect all currently supported versions of Citrix Hypervisor up to and including Citrix Hypervisor 8.2 LTSR.

These issues have the following identifiers:

CVE ID	Description	Type	Pre-requisites
CVE-2021-28038	An attacker with the ability to execute privileged mode code in a guest can perform a denial of service attack against the host	CWE-400: Uncontrolled Resource Consumption	Ability to run privileged code in a guest VM
CVE-2021-28688	An attacker with the ability to execute privileged mode code in a guest can perform a denial of service attack against the host	CWE-400: Uncontrolled Resource Consumption	Ability to run privileged code in a guest VM

An additional issue has been identified in Citrix Hypervisor 8.2 LTSR (only) that may allow malicious network traffic to cause subsequent packets to be dropped.

This issue has the following identifier:

CVE ID	Description	Type	Pre-requisites
CVE-2020-35498	Malicious network traffic on the local network may cause subsequent packets to be dropped	CWE-682: Incorrect Calculation	Access to the local network

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: CTX306481 – <https://support.citrix.com/article/CTX306481&gt; and CTX306423 – <https://support.citrix.com/article/CTX306423&gt;
Citrix XenServer 7.1 LTSR CU2: CTX306480 – <https://support.citrix.com/article/CTX306480&gt;
Citrix XenServer 7.0: CTX306482 – <https://support.citrix.com/article/CTX306482&gt;

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/&gt;.

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 <http://www.citrix.com/site/ss/supportContacts.asp&gt;.

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&gt;

Disclaimer

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 time.

Changelog

Date	Change
2021-03-30	Initial Publication