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

Severity: high (CVSS 8.8 v3.1)
Exploited in the wild: not listed in CISA KEV
EPSS: 0.1% probability of exploitation in the next 30 days
Public exploit or detection template: none known
Published: 2026-07-19 · updated 2026-10-27
Weakness: CWE-367

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.

Affected products

Linux kernel: from 6.11 before 6.12.93; from 6.13 before 6.18.35; from 6.19 before 7.0.12; 7.1-rc1, 7.1-rc2, 7.1-rc3, 7.1-rc4, 7.1-rc5 — fixed in 6.12.93, 6.18.35, 7.0.12
Linux kernel: 6.11 — fixed in 7.1

How to fix

Upgrade to a fixed version: Linux kernel 6.12.93, 6.18.35, 7.0.12; Linux kernel 7.1. Check the vendor advisory for mitigations.

References

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