CVE-2021-29657

Name: CVE-2021-29657
Creator: NVD / NIST
Published: 2021-07-22T17:15:09.47+00:00
License: https://creativecommons.org/publicdomain/zero/1.0/

HIGHCVSS 7.4/10EPSS 0.41%

Last modified Jun 17, 2026

CVE-2021-29657 is a high-severity vulnerability rated 7.4/10 on the CVSS scale. arch/x86/kvm/svm/nested.c in the Linux kernel before 5.11.12 has a use-after-free in which an AMD KVM guest can bypass access control on host OS MSRs when there are nested guests, aka CID-a58d9166a756. This occurs because of a TOCTOU race condition associated with a VMCB12 double fetch in nested_svm_vmrun.. EPSS estimates a 0.41% chance of exploitation in the next 30 days.

Description

arch/x86/kvm/svm/nested.c in the Linux kernel before 5.11.12 has a use-after-free in which an AMD KVM guest can bypass access control on host OS MSRs when there are nested guests, aka CID-a58d9166a756. This occurs because of a TOCTOU race condition associated with a VMCB12 double fetch in nested_svm_vmrun.

Metrics

CVSS 3.1

7.4/10

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

EPSS Probability

0.41%

32.9th percentile

Probability of exploitation in the next 30 days. Learn more

Weakness Enumeration

Affected Software

Vendor	Product	Versions
Linux	Linux Kernel	>= 5.10, < 5.10.28
Linux	Linux Kernel	>= 5.11, < 5.11.12

References

http://packetstormsecurity.com/files/163324/KVM-nested_svm_vmrun-Double-Fetch.htmlThird Party Advisory, VDB Entry
https://bugs.chromium.org/p/project-zero/issues/detail?id=2177Exploit, Mailing List, Patch, Third Party Advisory
https://cdn.kernel.org/pub/linux/kernel/v5.x/ChangeLog-5.11.12Exploit, Patch, Vendor Advisory
https://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git/commit/?id=a58d9166a756a0f4a6618e4f593232593d6df134Patch, Third Party Advisory
https://security.netapp.com/advisory/ntap-20210902-0008/Third Party Advisory
http://packetstormsecurity.com/files/163324/KVM-nested_svm_vmrun-Double-Fetch.htmlThird Party Advisory, VDB Entry
https://bugs.chromium.org/p/project-zero/issues/detail?id=2177Exploit, Mailing List, Patch, Third Party Advisory
https://cdn.kernel.org/pub/linux/kernel/v5.x/ChangeLog-5.11.12Exploit, Patch, Vendor Advisory
https://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git/commit/?id=a58d9166a756a0f4a6618e4f593232593d6df134Patch, Third Party Advisory
https://security.netapp.com/advisory/ntap-20210902-0008/Third Party Advisory

Timeline

Published: Jul 22, 2021
Last Modified: Jun 17, 2026
Status: Modified

Frequently Asked Questions

What is CVE-2021-29657?

How severe is CVE-2021-29657?

CVE-2021-29657 has a CVSS score of 7.4/10 (HIGH severity). The EPSS model estimates a 0.41% probability of exploitation in the next 30 days.

How do I fix CVE-2021-29657?

Check the vendor references and advisories linked above for patched versions and mitigation guidance. You can also run a Strix scan to test if your systems are affected.

Are you affected by CVE-2021-29657?

Run a free Strix scan to check your systems for this vulnerability.

Scan your code now

Source: NVD / NIST