CVE-2026-63939 Details
Description
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.
A vulnerability in the Linux kernel's KVM (Kernel-based Virtual Machine) SEV (Secure Encrypted Virtualization) implementation has been addressed. The issue arose in the management of the GHCB (Guest Hypervisor Communication Block) scratch area length when the area was located in the GHCB shared buffer. The vulnerability could lead to buffer overflows. The problem occurred because KVM initially handled the length correctly for most scenarios, but not for Page State Change (PSC) requests, where the length parameter only indicated the minimum required size. To rectify this, the length parameter has been renamed to better reflect its purpose, and the calculation of the scratch area length has been adjusted to prevent potential buffer overflows.
Users can upgrade to the latest version of the Linux kernel where this vulnerability has been fixed. Instructions for upgrading the kernel can be found in the official Linux kernel documentation.
Metrics
CVSS 4.0 Severity and Vector Strings:
No CVSS 4.0 data is available for this CVE.
CVSS 3.x Severity and Vector Strings:
No data available for CVSS Version 2.0 on this CVE.
No SSVC data is available for this CVE.
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Weakness Enumeration
No weakness enumeration is available for this CVE.
Affected Products
No affected product data is available for this CVE.
Change History
2 change records found show changes
| Date | Action | Recorded By |
|---|---|---|
| Jul 20, 2026 | CVE Modified | kernel.org |
| Jul 19, 2026 | New CVE Received | kernel.org |