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Vulnerability record · CVE-2021-3656 · published 4 March 2022

CVE-2021-3656: Linux kernel missing authorization vulnerability

Linux · Linux Kernel

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.

8.8 CVSS 3.1 High EPSS 0.66% · top 50.5% CWE-862 · Missing authorization
8.8CVSS 3.1 base score, v2 7.2
0.66%EPSS exploitation probability, 30 days
NoNot in CISA KEV
26Affected product versions listed by NVD
8References
17 Jun 2026Last modified by NVD

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.

CVSS:3.1/AV:L/AC:L/PR:L/UI:N/S:C/C:H/I:H/A:H

Affected products

26 vulnerable configurations from NVD's CPE data, grouped by vendor and product.

References

LinkTags
https://bugzilla.redhat.com/show_bug.cgi?id=1983988 Issue TrackingThird Party Advisory
https://git.kernel.org/pub/scm/virt/kvm/kvm.git/commit/?id=c7dfa4009965a9b2d7b329ee970eb8da0d32f0bc PatchThird Party Advisory
https://github.com/torvalds/linux/commit/c7dfa4009965a9b2d7b329ee970eb8da0d32f0bc PatchThird Party Advisory
https://www.openwall.com/lists/oss-security/2021/08/16/1 Mailing ListThird Party Advisory
https://bugzilla.redhat.com/show_bug.cgi?id=1983988 Issue TrackingThird Party Advisory
https://git.kernel.org/pub/scm/virt/kvm/kvm.git/commit/?id=c7dfa4009965a9b2d7b329ee970eb8da0d32f0bc PatchThird Party Advisory
https://github.com/torvalds/linux/commit/c7dfa4009965a9b2d7b329ee970eb8da0d32f0bc PatchThird Party Advisory
https://www.openwall.com/lists/oss-security/2021/08/16/1 Mailing ListThird Party Advisory

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Source: NIST National Vulnerability Database (record CVE-2021-3656), CISA KEV, FIRST EPSS (scores of 2026-09-26). This page is refreshed as NVD updates the record.