CVE-2026-63937
Received Received - Intake

KVM SEV TOCTOU Vulnerability in Linux Kernel

Publication date: 2026-07-19

Last updated on: 2026-07-19

Assigner: kernel.org

Description
In the Linux kernel, the following vulnerability has been resolved: KVM: SEV: Use READ_ONCE() when reading entries/indices from PSC buffer Use READ_ONCE() when reading entries/indices from the guest-accessible Page State Change buffer to defend against TOCTOU bugs. Don't bother with READ_ONCE()/WRITE_ONCE() for cases where KVM is writing (and not consuming the result!), as the guest isn't supposed to touch the buffer while it's being processed. I.e. using READ_ONCE() is all about protecting against misbehaving guests.

CVSS Scores

EPSS Scores

Probability:
Percentile:

Meta Information

Published
2026-07-19
Last Modified
2026-07-19
Generated
2026-07-20
AI Q&A
2026-07-19
EPSS Evaluated
N/A
NVD
CVE-2026-63937
EUVD
EUVD-2026-45710

Affected Vendors & Products

Showing 1 associated CPE
Vendor Product Version / Range
linux linux_kernel *

Helpful Resources

Exploitability

CWE
CWE Icon
KEV
KEV Icon
CWE ID Description
CWE-UNKNOWN

Attack-Flow Graph

AI Quick Actions

Instant insights powered by AI
Executive Summary

This vulnerability in the Linux kernel involves improper handling of the Page State Change (PSC) buffer in KVM (Kernel-based Virtual Machine) with SEV (Secure Encrypted Virtualization). The issue is that entries or indices read from the guest-accessible PSC buffer are not using READ_ONCE(), which could allow Time-of-Check Time-of-Use (TOCTOU) bugs. This means a misbehaving guest could potentially exploit race conditions to manipulate data.

Detection Guidance

This vulnerability is specific to the Linux kernel's KVM SEV implementation and requires kernel-level inspection. Detection involves checking kernel logs for related errors or verifying the kernel version against patched versions. Commands like 'dmesg | grep -i sev' or 'uname -a' may help identify affected systems.

Impact Analysis

If you use KVM with SEV on a Linux system, a malicious guest could potentially exploit this vulnerability to perform unauthorized actions or disrupt the host system by manipulating the PSC buffer. This could lead to data corruption, privilege escalation, or denial of service on the affected system.

Compliance Impact

This vulnerability does not directly affect compliance with GDPR, HIPAA, or similar standards as it pertains to a specific kernel memory handling issue in KVM SEV. No evidence suggests it impacts data protection or privacy requirements outlined in these regulations.

Mitigation Strategies

Apply the latest kernel patches from your Linux distribution that address this specific KVM SEV issue. Reboot the system after patching to ensure the updated kernel is active. Monitor vendor advisories for further updates.

Chat Assistant

Ask questions about this CVE
Hi! I’m here to help you understand CVE-2026-63937. Ask me anything about the vulnerability, its impact, or mitigation strategies.
0/70

EPSS Chart