SB20260720291 - Time-of-check Time-of-use (TOCTOU) Race Condition in Linux kernel kvm svm

Description

This security bulletin contains information about 1 vulnerability.

1) Time-of-check Time-of-use (TOCTOU) Race Condition (CVE-ID: CVE-2026-63937)

CWE-ID: CWE-367 - Time-of-check Time-of-use (TOCTOU) Race Condition

CVSSv4: 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]

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

The vulnerability exists due to a time-of-check time-of-use race condition in the KVM SEV Page State Change buffer handling in arch/x86/kvm/svm/sev.c when processing guest-accessible PSC buffer entries and indices. A local user can modify buffer values during processing to cause a denial of service.

The issue involves guest-accessible PSC buffer header fields and entries used for validation and array indexing.

Remediation

Install update from vendor's website.

References

• https://git.kernel.org/stable/c/b1dfaa6f7a957726a6800135be3659fbe4bbf2a4
• https://git.kernel.org/stable/c/bd232801ef1d1fd985d2d4ca3cd1d888303ca86f
• https://git.kernel.org/stable/c/c8cc238093ca6c99267032f6cfe78f59389f3157
• https://git.kernel.org/stable/c/edbbe88f83b524434974e84808d3093199d67c24