CVE-2021-29657: Linux Kernel

High severity, CVSS 7.4. EPSS: 0.4% chance of exploitation in the next 30 days.

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 Linux Kernel: from 5.10, before 5.10.28 (fixed in 5.10.28); from 5.11, before 5.11.12 (fixed in 5.11.12)

Published 2021-07-22. Last modified 2026-06-17.