US CISA warns of DoS flaws in Citrix Hypervisor

Citrix addressed vulnerabilities in Hypervisor that could be exploited by threat actors to execute code in a virtual machine to trigger a denial of service condition on the host.

US CISA warns that Citrix has released security updates to address flaws in Hypervisor that could be exploited by threat actors to execute code in a virtual machine to trigger a denial of service condition on the host.

Citrix Hypervisor (XenServer) is a high-performance hypervisor optimized for virtual app and desktop workloads and based on the Xen Project hypervisor.

“Citrix has released security updates to address vulnerabilities in Hypervisor (formerly XenServer). An attacker could exploit some of these vulnerabilities to cause a denial-of-service condition.” reads the advisory published by CISA.

“CISA encourages users and administrators to review Citrix Security Update CTX306565 and apply the necessary updates.”

The two vulnerabilities, tracked as CVE-2021-28038 and CVE-2021-28688, could be abused to cause the host to crash or become unresponsive. An attacker would have to be able to execute privileged code in a guest virtual machine.

“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.” reads the advisory published by Citrix.

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

The CVE-2021-28038 vulnerability is a Uncontrolled Resource Consumption issue, it could be exploited by an attacker with the ability to execute privileged mode code in a guest can perform a denial of service attack against the host.

“An issue was discovered in the Linux kernel through 5.11.3, as used with Xen PV. A certain part of the netback driver lacks necessary treatment of errors such as failed memory allocations (as a result of changes to the handling of grant mapping errors). A host OS denial of service may occur during misbehavior of a networking frontend driver.” reads the security advisory.

The flaw was caused by an incomplete fix for CVE-2021-26931.

The CVE-2021-28688 vulnerability is also an Uncontrolled Resource Consumption issue that impacts all Linux versions that include the fix for CVE-2021-26930 (XSA-365).

“A malicious or buggy frontend driver may be able to cause resource leaks from the corresponding backend driver. This can result in a host-wide Denial of Sevice (DoS).” reads the advisory.

Citrix also fixed another issue, tracked CVE-2020-35498, that affects Hypervisor 8.2 LTSR only, and which could result in malicious network traffic causing subsequent packets to be dropped.

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Pierluigi Paganini

(SecurityAffairs – hacking, CITRIX)

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Pierluigi Paganini

Pierluigi Paganini is member of the ENISA (European Union Agency for Network and Information Security) Threat Landscape Stakeholder Group and Cyber G7 Group, he is also a Security Evangelist, Security Analyst and Freelance Writer. Editor-in-Chief at "Cyber Defense Magazine", Pierluigi is a cyber security expert with over 20 years experience in the field, he is Certified Ethical Hacker at EC Council in London. The passion for writing and a strong belief that security is founded on sharing and awareness led Pierluigi to find the security blog "Security Affairs" recently named a Top National Security Resource for US. Pierluigi is a member of the "The Hacker News" team and he is a writer for some major publications in the field such as Cyber War Zone, ICTTF, Infosec Island, Infosec Institute, The Hacker News Magazine and for many other Security magazines. Author of the Books "The Deep Dark Web" and “Digital Virtual Currency and Bitcoin”.