CVE-2021-29657

What it is

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.

At a glance

Exploitability

Can be exploited locally on the machine without logging in. High risk of data exposure, data tampering, service disruption.

Exploit odds

0.4% chance of exploitation in the next 30 days (EPSS).

Fix

A patch, advisory or fixed version is referenced. Upgrade or apply it.

Timeline

1. 2021-07-22 17:15 UTC PublishedDisclosed publicly on CVE.org and NVD
2. 2026-06-17 03:48 UTC Last updatedMost recent change to the record

Why it ranks here

• Exploited in the wild: no, CISA does not list it.
• Exploit odds: 0.4% in the next 30 days (EPSS).
• Severity: 7.4 HIGH (CVSS).
• Fix: a patch or advisory is linked.

Details

Published

2021-07-22 17:15 UTC

Last modified

2026-06-17 03:48 UTC

Exploit probability

0.4% · EPSS, next 30 days

Weakness

CWE-367

Record status

Modified

Affected

• Linux Kernel < 5.10.28
• Linux Kernel < 5.11.12

Attack profile CVSS 3.1 · 7.4

Attack vector

Local

Complexity

High

Privileges needed

None

User interaction

None

Scope

Unchanged

Confidentiality

High

Integrity

High

Availability

High

Is it in your code?

Hand this to your coding agent. It searches your project for the affected products and checks versions. Nothing leaves your machine.

Read https://cve-list.com/agent/cve/CVE-2021-29657.md and follow it. Check whether this project is affected by CVE-2021-29657. Read only. Don't change anything and don't upload my code. Tell me yes, no or not sure, with the file as proof.

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