Is CVE-2021-3656 being actively exploited?

CVE-2021-3656 is not currently listed in the CISA Known Exploited Vulnerabilities (KEV) catalog.

What is the CVSS score for CVE-2021-3656?

CVE-2021-3656 has a CVSS 3.1 base score of 8.8 (HIGH).

CVE-2021-3656

HIGH · CVSS 8.8EPSS 0.7%EU EUVD

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.

Key facts

CVSS score: 8.8 (v3.1)
Severity: HIGH
CVSS vector: CVSS:3.1/AV:L/AC:L/PR:L/UI:N/S:C/C:H/I:H/A:H
Weakness (CWE): CWE-862
EPSS score: 0.7% (50th percentile)
In CISA KEV: No
In EU EUVD: Yes (EUVD-2021-26951)
Published: March 4, 2022
NVD last modified: June 17, 2026
Status: Modified

EU Vulnerability Database (EUVD)

This vulnerability is also tracked by ENISA as EUVD-2021-26951 in the EU Vulnerability Database. Last updated in EUVD on August 3, 2024.

View on the EU Vulnerability Database

Affected products

fedoraproject / fedora
fedoraproject / fedora
linux / linux kernel
linux / linux kernel
linux / linux kernel
linux / linux kernel
linux / linux kernel
linux / linux kernel
linux / linux kernel
linux / linux kernel
redhat / 3scale api management
redhat / codeready linux builder
redhat / enterprise linux
redhat / enterprise linux
redhat / enterprise linux desktop
redhat / enterprise linux eus
redhat / enterprise linux eus
redhat / enterprise linux eus
redhat / enterprise linux for ibm z systems
redhat / enterprise linux for ibm z systems
redhat / enterprise linux for ibm z systems eus
redhat / enterprise linux for ibm z systems eus
redhat / enterprise linux for ibm z systems eus
redhat / enterprise linux for power big endian
redhat / enterprise linux for power little endian
redhat / enterprise linux for power little endian
redhat / enterprise linux for power little endian eus
redhat / enterprise linux for power little endian eus
redhat / enterprise linux for power little endian eus
redhat / enterprise linux for real time
redhat / enterprise linux for real time
redhat / enterprise linux for real time for nfv
redhat / enterprise linux for real time for nfv
redhat / enterprise linux for real time for nfv tus
redhat / enterprise linux for real time for nfv tus
redhat / enterprise linux for real time tus
redhat / enterprise linux for real time tus
redhat / enterprise linux for scientific computing
redhat / enterprise linux server
redhat / enterprise linux server aus
redhat / enterprise linux server aus
redhat / enterprise linux server aus
redhat / enterprise linux server aus
redhat / enterprise linux server for power little endian update services for sap solutions
redhat / enterprise linux server for power little endian update services for sap solutions
redhat / enterprise linux server for power little endian update services for sap solutions
redhat / enterprise linux server for power little endian update services for sap solutions
redhat / enterprise linux server tus
redhat / enterprise linux server tus
redhat / enterprise linux server tus

and 10 more…

Certified products that may be affected

26 FIPS 140 or Common Criteria certified products, from automated matching by sec-certs.org.

Red Hat Enterprise Linux 8 NSS Cryptographic Module - Red Hat, Inc. - FIPS 140 5513 - active
Red Hat Enterprise Linux 8 Kernel Cryptographic API - Red Hat, LLC - FIPS 140 5461 - active
Red Hat Enterprise Linux 8 Kernel Cryptographic API - Red Hat, Inc. - FIPS 140 5089 - active
Red Hat Enterprise Linux 8 OpenSSL Cryptographic Module - Red Hat®, Inc. - FIPS 140 4642 - historical
Red Hat Enterprise Linux 8 NSS Cryptographic Module - Red Hat®, Inc. - FIPS 140 4458 - historical

See all 26 in the Security Certifications Explorer.

References

https://bugzilla.redhat.com/show_bug.cgi?id=1983988(Issue Tracking, Third Party Advisory)
https://git.kernel.org/pub/scm/virt/kvm/kvm.git/commit/?id=c7dfa4009965a9b2d7b329ee970eb8da0d32f0bc(Patch, Third Party Advisory)
https://github.com/torvalds/linux/commit/c7dfa4009965a9b2d7b329ee970eb8da0d32f0bc(Patch, Third Party Advisory)
https://www.openwall.com/lists/oss-security/2021/08/16/1(Mailing List, Third Party Advisory)

Last updated September 17, 2026 · Source: NVD, CISA KEV, FIRST.org EPSS

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