Out-of-bounds read in Linux kernel - CVE-2026-63938

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Main Vulnerability Database Vulnerabilities #VU138708

Out-of-bounds read in Linux kernel - CVE-2026-63938

Published: July 20, 2026


Vulnerability identifier: #VU138708
CSH Severity: Low
CVSS v4: 6.8 [CVSS:4.0/AV:L/AC:L/AT:N/PR:L/UI:N/VC:N/VI:N/VA:H/SC:N/SI:N/SA:N]
CVE-ID: CVE-2026-63938
CWE-ID: CWE-125
Exploitation vector: Local access
Exploit availability: No public exploit available

Vulnerability details

The vulnerability allows a local user to cause a denial of service.

The vulnerability exists due to an out-of-bounds read in the KVM SEV PSC request handling in arch/x86/kvm/svm/sev.c when processing Page State Change requests with indices that exceed the effective scratch buffer size. A local user can provide a crafted PSC buffer pointer and PSC indices to cause a denial of service.

The issue arises if the guest-provided pointer is not exactly at the start of the GHCB shared buffer, which can reduce the effective size of the scratch area.


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-2026-63938

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