Improper access control in Linux kernel - CVE-2026-63941

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Main Vulnerability Database Vulnerabilities #VU138711

Improper access control in Linux kernel - CVE-2026-63941

Published: July 20, 2026


Vulnerability identifier: #VU138711
CSH Severity: Low
CVSS v4: 4.8 [CVSS:4.0/AV:L/AC:L/AT:N/PR:L/UI:N/VC:N/VI:L/VA:N/SC:N/SI:N/SA:N]
CVE-ID: CVE-2026-63941
CWE-ID: CWE-284
Exploitation vector: Local access
Exploit availability: No public exploit available

Vulnerability details

The vulnerability allows a local user to bypass intended vector length restrictions for a nested guest.

The vulnerability exists due to improper access control in the KVM arm64 nested virtualization SVE register handling for ZCR_EL2 when restoring SVE context for an L2 guest after handling guest hypervisor updates through ZCR_EL1. A local user can write an uncapped ZCR_EL2 value via ZCR_EL1 to bypass intended vector length restrictions for a nested guest.

The issue affects VHE guest hypervisor scenarios in nested virtualization on arm64 systems with SVE enabled.


Affected software

Linux kernel
Ubuntu
linux-ibm (Ubuntu package)
linux-azure (Ubuntu package)
linux-aws (Ubuntu package)
linux-nvidia (Ubuntu package)
linux-nvidia-bos (Ubuntu package)

How to mitigate CVE-2026-63941

Install security update from vendor's repository.

Linux kernel - update to 7.0 rc3
linux-ibm (Ubuntu package) - addressed in versions 7.0.0-1008.8, 7.0.0-1010.10
linux-azure (Ubuntu package) - addressed in versions 7.0.0-1009.9, 7.0.0-1010.10
linux-aws (Ubuntu package) - addressed in versions 7.0.0-1009.9, 7.0.0-1015.15
linux-nvidia (Ubuntu package) - addressed in versions 7.0.0-1016.16, 7.0.0-1016.16~24.04.1
linux-nvidia-bos (Ubuntu package) - update to 7.0.0-2016.16

External References

Related Security Bulletins