SB20260425154 - Improper access control in Linux kernel kernel cpu

Description

This security bulletin contains information about 1 vulnerability.

1) Improper access control (CVE-ID: CVE-2026-31561)

CWE-ID: CWE-284 - Improper Access Control

CVSSv4: CVSS:4.0/AV:L/AC:L/AT:N/PR:H/UI:N/VC:H/VI:H/VA:H/SC:N/SI:N/SA:N/E:U/U:Clear

The vulnerability allows a local privileged user to disable security protections.

The vulnerability exists due to improper access control in CR4 pinning logic when modifying CR4 during early boot on application processors that are not online yet. A local privileged user can modify the online bit in writable memory and disable CR4 pinning to disable SMAP/SMEP and disable security protections.

The issue is particularly relevant in SEV-ES, SEV-SNP, or TDX guest environments during a short early-boot window.

Remediation

Install update from vendor's website.

References

• https://git.kernel.org/stable/c/00d956dafa76f86a73424fe5cce3d604a8be2e4b
• https://git.kernel.org/stable/c/411df123c017169922cc767affce76282b8e6c85
• https://git.kernel.org/stable/c/a6e14114684d2324e5401617d6d01acb4a4e0e22
• https://git.kernel.org/stable/c/d7853d9fe94abf43b46c57b0b7f8418198b7615a