How severe is CVE-2021-29657?

CVE-2021-29657 has a CVSS 3.x base score of 7.4, rated high severity. It is exploitable over local access with high attack complexity, requires no privileges and no user interaction. Impact on confidentiality is high, integrity high, and availability high.

Is CVE-2021-29657 being actively exploited?

It is not currently listed in CISA's KEV catalog. Its EPSS exploit-prediction score is 0% (33rd percentile), an estimate of the probability of exploitation in the next 30 days.

What products are affected by CVE-2021-29657?

CVE-2021-29657 affects Linux Linux Kernel. See the affected-products list for the exact vulnerable versions.

How do I fix CVE-2021-29657?

Review the linked vendor and NVD advisories for patched versions and mitigations, then upgrade or apply the recommended workaround. Given its high severity, prioritise patching exposed systems.

When was CVE-2021-29657 published?

CVE-2021-29657 was published on 2021-07-22 and last updated on 2026-06-17.

CVE-2021-29657

CVE-2021-29657 is a high-severity vulnerability in Linux Linux Kernel with a CVSS 3.x base score of 7.4. It is not currently listed as actively exploited by CISA, and its EPSS exploit-prediction score is low. The underlying weakness is classified as CWE-367.

Key facts

Severity: High (CVSS 3.x base score 7.4)
CVSS v2: 6.9
EPSS exploit prediction: 0% (33rd percentile)
Actively exploited: Not listed in CISA KEV
Weakness: CWE-367
Affected product: Linux Linux Kernel
Published: 2021-07-22
Last modified: 2026-06-17

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.

Frequently asked questions

What is CVE-2021-29657?: 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.
How severe is CVE-2021-29657?: CVE-2021-29657 has a CVSS 3.x base score of 7.4, rated high severity. It is exploitable over local access with high attack complexity, requires no privileges and no user interaction. Impact on confidentiality is high, integrity high, and availability high.
Is CVE-2021-29657 being actively exploited?: It is not currently listed in CISA's KEV catalog. Its EPSS exploit-prediction score is 0% (33rd percentile), an estimate of the probability of exploitation in the next 30 days.
What products are affected by CVE-2021-29657?: CVE-2021-29657 affects Linux Linux Kernel. See the affected-products list for the exact vulnerable versions.
How do I fix CVE-2021-29657?: Review the linked vendor and NVD advisories for patched versions and mitigations, then upgrade or apply the recommended workaround. Given its high severity, prioritise patching exposed systems.
When was CVE-2021-29657 published?: CVE-2021-29657 was published on 2021-07-22 and last updated on 2026-06-17.

References

Affected products (1)

cpe:2.3:o:linux:linux_kernel:*:*:*:*:*:*:*:*

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