CVE-2026-63937 KVM: SEV: Use READ_ONCE() when reading entries/indices from PSC buffer
A race condition in KVM SEV allows a malicious guest to exploit TOCTOU bugs in the PSC buffer, potentially leading to privilege escalation or code execution.
- Exploited in the wild
- Not known
- Login needed
- Any signed-in user
- Attackable
- Local or same network only
- Victim action needed
- Not needed
- Fix
- Available
What is CVE-2026-63937?
CVE-2026-63937 is a high-severity vulnerability in Linux kernel, published on 19 Jul 2026. It can only be exploited from the same machine or local network, with no action from the victim.
Official 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.
Weakness: CWE-367
Which versions are affected by CVE-2026-63937?
It affects 1 product.
Products include Linux kernel.
How do I fix CVE-2026-63937?
Apply the vendor's patch.
Is CVE-2026-63937 being exploited?
There is no known exploitation of CVE-2026-63937 in the wild and no public exploit code.
Other vulnerabilities in Linux kernel
Sources
Also known as BELL-CVE-2026-63937, DEBIAN-CVE-2026-63937, GHSA-vv26-frjx-jxxh, UBUNTU-CVE-2026-63937.