CVE-2021-29657

Severity: high (CVSS 7.4 v3.1)
Exploited in the wild: not listed in CISA KEV
EPSS: 0.4% probability of exploitation in the next 30 days
Public exploit or detection template: yes
Published: 2021-07-22 · updated 2026-06-17
Weakness: CWE-367

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.

Affected products

Linux kernel: from 5.10 before 5.10.28; from 5.11 before 5.11.12 — fixed in 5.10.28, 5.11.12

How to fix

Upgrade to a fixed version: Linux kernel 5.10.28, 5.11.12. Check the vendor advisory for mitigations.

References

http://packetstormsecurity.com/files/163324/KVM-nested_svm_vmrun-Double-Fetch.html
https://bugs.chromium.org/p/project-zero/issues/detail?id=2177
https://cdn.kernel.org/pub/linux/kernel/v5.x/ChangeLog-5.11.12
https://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git/commit/?id=a58d9166a756a0f4a6618e4f593232593d6df134
https://security.netapp.com/advisory/ntap-20210902-0008/
http://packetstormsecurity.com/files/163324/KVM-nested_svm_vmrun-Double-Fetch.html
https://bugs.chromium.org/p/project-zero/issues/detail?id=2177
https://cdn.kernel.org/pub/linux/kernel/v5.x/ChangeLog-5.11.12
https://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git/commit/?id=a58d9166a756a0f4a6618e4f593232593d6df134
https://security.netapp.com/advisory/ntap-20210902-0008/

Get alerted when CVE-2021-29657 or the next vulnerability affects your stack