High · CVSS 8.8CVE-2026-63937

KVM: SEV: Use READ_ONCE() when reading entries/indices from PSC bufferCVE-2026-63937

Answer in brief

CVE-2026-63937 records a High severity (CVSS 8.8) vulnerability in KVM: SEV: Use READ_ONCE() when reading entries/indices from PSC buffer. The current sources do not mark it as known exploited. The current feed maps Linux/Linux (generic), Linux/Linux (generic). Check affected ranges and fixed versions before updating.

Analysis pending evidence review

HOL Guard separates source facts from reviewed analysis. See the methodology.

Published Jul 19, 2026Updated Oct 27, 2026Source checked Nov 4, 2026First seen by HOL Aug 5, 2026Material review Oct 27, 2026

Upstream Advisory

Key facts

Risk: High · CVSS 8.8
Exploitation: Not marked as known exploited
Affected software: 8 mapped packages or products
Fix availability: Available

Why this deserves its current priority

CVSS is 8.8. The current sources do not mark it as known exploited. Treat this as a source-backed prioritization signal, not a statement about your environment.

Analysis status

Analysis pending evidence review

Factual feed record only; HOL analysis is not approved for indexing. Read the methodology.

Affected scope and exposure questions

The current feed maps Linux/Linux (generic), Linux/Linux (generic). Check affected ranges and fixed versions before updating.

Affected products and reported versions
Product	Affected versions	Fixed versions
cpe:2.3:o:linux:linux_kernel::::::::	Not reported	Not reported
cpe:2.3:o:linux:linux_kernel:7.1:rc1::::::	Not reported	Not reported
cpe:2.3:o:linux:linux_kernel:7.1:rc2::::::	Not reported	Not reported
cpe:2.3:o:linux:linux_kernel:7.1:rc3::::::	Not reported	Not reported
cpe:2.3:o:linux:linux_kernel:7.1:rc4::::::	Not reported	Not reported
cpe:2.3:o:linux:linux_kernel:7.1:rc5::::::	Not reported	Not reported

Mapped affected packages and fixed versions
Package	Affected range	Fixed version
Linux/Linuxgeneric	>=9b54e248d2644be71cb394eb85f31ad99e023a05 <bd232801ef1d1fd985d2d4ca3cd1d888303ca86f \|\| >=9b54e248d2644be71cb394eb85f31ad99e023a05 <b1dfaa6f7a957726a6800135be3659fbe4bbf2a4 \|\| >=9b54e248d2644be71cb394eb85f31ad99e023a05 <edbbe88f83b524434974e84808d3093199d67c24 \|\| >=9b54e248d2644be71cb394eb85f31ad99e023a05 <c8cc238093ca6c99267032f6cfe78f59389f3157	bd232801ef1d1fd985d2d4ca3cd1d888303ca86f, b1dfaa6f7a957726a6800135be3659fbe4bbf2a4, edbbe88f83b524434974e84808d3093199d67c24, c8cc238093ca6c99267032f6cfe78f59389f3157
Linux/Linuxgeneric	6.11	Not reported

Recommended response

Check inventory. Check lockfiles and deployed manifests for Linux/Linux, Linux/Linux.
Review the reported fix. Update Linux/Linux to bd232801ef1d1fd985d2d4ca3cd1d888303ca86f if you use the affected versions. Test the change in a non-production environment first.

Evidence timeline and material changes

Published upstream
Jul 19, 2026
Evidence: source:cvelist:source_dates:source-dates:record
Source modified
Oct 27, 2026
Evidence: source:cvelist:source_dates:source-dates:record
First seen by HOL
Aug 5, 2026

Sources and claim methodology

Upstream source 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.

Quoted source text, attributed separately from HOL analysis.

Time-of-check/time-of-use double fetch in the Zephyr i3c_transfer() syscall handler allows kernel-mode control-flow hijack from user modeAlso CWE-367