Zapscape: KVM/x86 use-after-free lets guests escape to host
CVE-2026-64561 corrupts host shadow pages from untrusted guests when nested virtualization is exposed, especially on multi-tenant clouds.
A use-after-free in KVM’s x86 shadow MMU, disclosed as Zapscape (CVE-2026-64561), lets a malicious guest break out to the host on both Intel and AMD systems.
The flaw sits in the recursive reclaim path that tears down shadow pages. Guest-controlled actions alone can free a still-active shadow page and corrupt host kernel state, undermining guest-host isolation on machines that take untrusted tenants and expose nested virtualization. Multi-tenant x86 public clouds are the clearest practical target.
On Intel hosts the bug is reachable only when both 4-level and 5-level EPT walks are offered to the level-1 guest. AMD systems have no equivalent gate. The issue is distinct from the earlier Januscape escape (CVE-2026-53359).
Hyunwoo Kim reported the vulnerability; it is fixed in mainline Linux. Operators who run nested KVM for untrusted workloads should treat host updates as urgent.