Heap-based buffer overflow in Linux kernel - CVE-2026-63939

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Main Vulnerability Database Vulnerabilities #VU138709

Heap-based buffer overflow in Linux kernel - CVE-2026-63939

Published: July 20, 2026


Vulnerability identifier: #VU138709
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-2026-63939
CWE-ID: CWE-122
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 a heap-based buffer overflow in the KVM SEV GHCB scratch area handling in arch/x86/kvm/svm/sev.c when processing PSC requests with a guest-provided scratch area pointer. A local user can provide a crafted scratch area pointer and length values to cause a denial of service.

The issue occurs when the scratch area is located in the GHCB shared buffer, where only the minimum header length was tracked instead of the full effective scratch area size.


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-2026-63939

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