PT-2026-61256 · Linux · Linux

CVE-2026-63939 · Published 2026-07-19 · Updated 2026-07-19

NVD

CVSS v3.1

9.3

Critical

Base vector

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

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.

Fix

Related Identifiers

CVE-2026-63939

Affected Products

Linux

References · 5

• https://nvd.nist.gov/vuln/detail/CVE-2026-63939 · Security Note
• https://git.kernel.org/stable/c/5867d7e202e09f037cefe77f7af4413c7c0fa088 · Note
• https://git.kernel.org/stable/c/9f0a9e780f02c02d025a190f1885e1d1d73b87bd · Note
• https://git.kernel.org/stable/c/6ca9400d36005ffdca25f80186bea781c7e1dc4c · Note
• https://git.kernel.org/stable/c/6644565527c4c5f507088b1c9ddf72de47790b68 · Note