Linux kernel KVM SEV flaw can allow guest-to-host buffer overflow and potential host compromise; impacts virtualization infrastructure widely used in cloud and enterprise.
CVE-2026-63939
KVM SEV GHCB buffer overflow allows guest-to-host compromise.
Is CVE-2026-63939 being exploited?
Not confirmed. CVE-2026-63939 does not appear in CISA's Known Exploited Vulnerabilities catalog, which records only exploitation that has been observed and reported publicly. That is evidence of absence of a report, not evidence the flaw is unattacked. EPSS currently estimates a 0.19% probability of exploitation in the next 30 days.
How severe is CVE-2026-63939?
CVE-2026-63939 is rated Critical with a CVSS score of 9.3. Severity describes how bad exploitation would be, not how likely it is: pair it with exploitation evidence before deciding what to patch first.
Is there a patch for CVE-2026-63939?
Yes. A fix has been recorded for CVE-2026-63939. The vendor advisory is the authority on the exact fixed version — apply it from there rather than from a summary.
What does CVE-2026-63939 affect?
CVE-2026-63939 affects Linux kernel with KVM and AMD SEV enabled, Virtualization hosts, Cloud providers using SEV, GHCB/PSC guest interfaces. Confirm the exact affected versions against the vendor advisory before deciding you are exposed.
What should I do about CVE-2026-63939?
Apply vendor Linux kernel KVM/SEV patches immediately; isolate or suspend SEV guests until patched.
Exploitation status reflects CISA's KEV catalog as we last synced it. Check the catalog directly.
Guest-crafted PSC requests can overflow GHCB scratch area in KVM SEV, enabling guest-to-host escape, arbitrary code execution, or host compromise.
Immediate action required
- affected>= 9b54e248d2644be71cb394eb85f31ad99e023a05 and < 6ca9400d36005ffdca25f80186bea781c7e1dc4c
- affected>= 9b54e248d2644be71cb394eb85f31ad99e023a05 and < 9f0a9e780f02c02d025a190f1885e1d1d73b87bd
- affected>= 9b54e248d2644be71cb394eb85f31ad99e023a05 and < 6644565527c4c5f507088b1c9ddf72de47790b68
- affected>= 9b54e248d2644be71cb394eb85f31ad99e023a05 and < 5867d7e202e09f037cefe77f7af4413c7c0fa088
- affected6.11
As published in the CVE Program record. A version outside these ranges is not a statement that it is unaffected — vendors sometimes understate a range, and distribution-backported builds carry upstream numbers that do not reflect what was patched into them.