CVE-2021-3656 Privilege escalation in KVM

What is CVE-2021-3656?

CVE-2021-3656 is a high-severity vulnerability in Fedoraproject Fedora, published on 4 Mar 2022. It can only be exploited from the same machine or local network, with no action from the victim.

Official description

A flaw was found in the KVM's AMD code for supporting SVM nested virtualization. The flaw occurs when processing the VMCB (virtual machine control block) provided by the L1 guest to spawn/handle a nested guest (L2). Due to improper validation of the "virt_ext" field, this issue could allow a malicious L1 to disable both VMLOAD/VMSAVE intercepts and VLS (Virtual VMLOAD/VMSAVE) for the L2 guest. As a result, the L2 guest would be allowed to read/write physical pages of the host, resulting in a crash of the entire system, leak of sensitive data or potential guest-to-host escape.

Weakness: CWE-862

Which versions are affected by CVE-2021-3656?

It affects 26 products.

Products include Fedoraproject Fedora, Linux kernel, Redhat 3scale Api Management, Redhat Codeready Linux Builder, Redhat Enterprise Linux, Redhat Enterprise Linux Desktop and 20 more.

How do I fix CVE-2021-3656?

Apply the vendor's patch.

Is CVE-2021-3656 being exploited?

There is no known exploitation of CVE-2021-3656 in the wild and no public exploit code.

Public exploit code: 1 proofs of concept on GitHub.

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All Fedoraproject Fedora vulnerabilities

Sources

• CVE record
• NVD
• OSV
• How this page is made

Also known as DEBIAN-CVE-2021-3656, UBUNTU-CVE-2021-3656.