Integer underflow in Linux kernel - CVE-2026-63940

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Main Vulnerability Database Vulnerabilities #VU138710

Integer underflow in Linux kernel - CVE-2026-63940

Published: July 20, 2026


Vulnerability identifier: #VU138710
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-2026-63940
CWE-ID: CWE-191
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 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.


Affected software

Linux kernel
openEuler
Ubuntu
python3-perf-debuginfo
python3-perf
perf-debuginfo
perf
kernel-tools-devel
kernel
bpftool
bpftool-debuginfo
kernel-debuginfo
kernel-debugsource
kernel-devel
kernel-headers
kernel-source
kernel-tools
kernel-tools-debuginfo
linux-nvidia-tegra (Ubuntu package)
linux-ibm (Ubuntu package)
linux-aws (Ubuntu package)
linux-azure (Ubuntu package)
linux-gcp-7.0 (Ubuntu package)
linux-oracle-7.0 (Ubuntu package)
linux-azure-7.0 (Ubuntu package)
linux-nvidia (Ubuntu package)
linux-nvidia-bos (Ubuntu package)

How to mitigate CVE-2026-63940

Install security update from vendor's repository.

Linux kernel - update to 7.0 rc3
python3-perf-debuginfo - update to 5.10.0-328.0.0.229
python3-perf - update to 5.10.0-328.0.0.229
perf-debuginfo - update to 5.10.0-328.0.0.229
perf - update to 5.10.0-328.0.0.229
kernel-tools-devel - update to 5.10.0-328.0.0.229
kernel - update to 5.10.0-328.0.0.229
bpftool - update to 5.10.0-328.0.0.229
bpftool-debuginfo - update to 5.10.0-328.0.0.229
kernel-debuginfo - update to 5.10.0-328.0.0.229
kernel-debugsource - update to 5.10.0-328.0.0.229
kernel-devel - update to 5.10.0-328.0.0.229
kernel-headers - update to 5.10.0-328.0.0.229
kernel-source - update to 5.10.0-328.0.0.229
kernel-tools - update to 5.10.0-328.0.0.229
kernel-tools-debuginfo - update to 5.10.0-328.0.0.229
linux-nvidia-tegra (Ubuntu package) - update to 6.8.0-1035.38
linux-ibm (Ubuntu package) - addressed in versions 7.0.0-1008.8, 7.0.0-1010.10
linux-aws (Ubuntu package) - addressed in versions 7.0.0-1009.9, 7.0.0-1015.15
linux-azure (Ubuntu package) - addressed in versions 7.0.0-1009.9, 7.0.0-1010.10
linux-gcp-7.0 (Ubuntu package) - update to 7.0.0-1011.11~24.04.1
linux-oracle-7.0 (Ubuntu package) - update to 7.0.0-1011.11~24.04.1
linux-azure-7.0 (Ubuntu package) - update to 7.0.0-1014.14~24.04.1
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