CVE-2026-63939

9.3 CRITICAL 0.2% exploit odds Fix listed Memory safety OS & kernel

What it is

In the Linux kernel, the following vulnerability has been resolved: KVM: SEV: Compute the correct max length of the in-GHCB scratch area When setting the length of the GHCB scratch area, and the area is in the GHCB shared buffer, set the effective length of the scratch area to the max possible size given the start of the guest-provided pointer, and the end of the shared buffer. The code was "fine" when first introduced, as KVM doesn't consult the length of the buffer when emulating MMIO, because the passed in @len always specifies the *max* size required. But for PSC requests, the incoming @len is just the minimum length (to process the header), and KVM needs to know the full size of the scratch area to avoid buffer overflows (spoiler alert). Opportunistically rename @len => @min_len to better reflect its role.

At a glance

Exploitability: Can be exploited locally on the machine without logging in. High risk of data exposure, data tampering, service disruption.
Exploit odds: 0.2% chance of exploitation in the next 30 days (EPSS).
Fix: A patch, advisory or fixed version is referenced. Upgrade or apply it.

Timeline

2026-07-19 16:17 UTC PublishedDisclosed publicly on CVE.org and NVD
2026-10-28 18:33 UTC Last updatedMost recent change to the record

Why it ranks here

Exploited in the wild: no, CISA does not list it.
Exploit odds: 0.2% in the next 30 days (EPSS).
Severity: 9.3 CRITICAL (CVSS).
Fix: a patch or advisory is linked.

Details

Published: 2026-07-19 16:17 UTC
Last modified: 2026-10-28 18:33 UTC
Exploit probability: 0.2% · EPSS, next 30 days
Weakness: CWE-122
Record status: Analyzed

Affected

Linux Kernel < 6.12.93
Linux Kernel < 6.18.35
Linux Kernel < 7.0.12
Linux Kernel 7.1

Attack profile CVSS 3.1 · 9.3

Attack vector: Local
Complexity: Low
Privileges needed: None
User interaction: None
Scope: Changed
Confidentiality: High
Integrity: High
Availability: High

Raw vector

CVSS:3.1/AV:L/AC:L/PR:N/UI:N/S:C/C:H/I:H/A:H

Is it in your code?

Hand this to your coding agent. It searches your project for the affected products and checks versions. Nothing leaves your machine.

Read https://cve-list.com/agent/cve/CVE-2026-63939.md and follow it. Check whether this project is affected by CVE-2026-63939. Read only. Don't change anything and don't upload my code. Tell me yes, no or not sure, with the file as proof.

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Fix and advisories

References

NVD record · CVE.org record