Integer underflow in Linux kernel - CVE-2026-63940
Published: July 20, 2026
Vulnerability identifier: #VU138710
CSH Severity: Low
CVSS v4.0: 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/E:U/U:Clear
CVE-ID: CVE-2026-63940
CWE-ID: CWE-191
Exploitation vector: Local access
Exploit availability:
No public exploit available
Vendor: Linux Foundation
Affected software:
Linux kernel
Linux kernel
Detailed vulnerability description
The vulnerability allows a local user to cause a denial of service.
The vulnerability exists due to an integer underflow in KVM SEV Port I/O handling in arch/x86/kvm/svm/sev.c when processing Port I/O requests with a length or count of 0. A local user can trigger a zero-length Port I/O request to cause a denial of service.
The issue affects the handling of VMGEXIT and string I/O requests in the KVM SEV implementation.
How to mitigate CVE-2026-63940
Install security update from vendor's repository.