CVE-2026-63939
CriticalCVSS 9.3Exploitation Probability (EPSS)
Low risk10th percentile - higher than 10% of all known CVEs
Summary
In the Linux kernel KVM SEV module, a vulnerability was found due to incorrect calculation of the maximum scratch area length in GHCB. This bug can cause a buffer overflow when processing PSC requests if the minimum length is passed instead of the full size.
Risk Assessment
The organization is at risk of a buffer overflow in KVM with SEV virtualization, potentially allowing a malicious guest to corrupt host memory or cause a denial of service.
Recommendation
Immediately update the Linux kernel to a version containing the fix (commit correcting the GHCB scratch area length calculation).
Original NVD description (English source)
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.