CVE-2021-29657 Use after free in n/a

What is CVE-2021-29657?

CVE-2021-29657 is a high-severity use after free vulnerability in Linux kernel, published on 22 Jul 2021. It can only be exploited from the same machine or local network, with no action from the victim.

Official 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.

Weakness: CWE-416, CWE-367

Which versions are affected by CVE-2021-29657?

It affects 1 product.

Products include Linux kernel.

How do I fix CVE-2021-29657?

Apply the vendor's patch.

Upgrade to the fixed version. These bugs are found with fuzzing and sanitisers and avoided by memory-safe languages. More about Use after free.

Is CVE-2021-29657 being exploited?

There is no known exploitation of CVE-2021-29657 in the wild and no public exploit code.

Other vulnerabilities in Linux kernel

• CVE-2026-53266 Linux Kernel Out-of-Bounds Write Exploited High 8.8
• CVE-2013-6282 Linux Kernel Improper Input Validation Exploited High 8.8
• CVE-2022-0185 Linux Kernel Heap-Based Buffer Overflow Exploited High 8.4
• CVE-2013-2094 Linux Kernel Privilege Escalation Exploited High 8.4
• CVE-2026-53362 Linux Kernel Unspecified Exploited High 7.8

All Linux kernel vulnerabilities

Sources

• CVE record
• NVD
• OSV
• GitHub advisory
• How this page is made

Also known as AZL-6554, DEBIAN-CVE-2021-29657, GHSA-m46m-jr5m-g95h, UBUNTU-CVE-2021-29657.