Zapscape KVM/x86 Flaw Enables Guest-to-Host Escape via Shadow MMU Use-After-Free
Vulnerability Disclosure · 2 sources · Updated 3mo ago · First seen Aug 6, 2026
A public disclosure detailed Zapscape, tracked as CVE-2026-64561, a guest-to-host escape vulnerability in KVM/x86 caused by a use-after-free in shadow MMU emulation. The flaw occurs in the recursive shadow-page "zap" path and can be triggered through guest-side actions alone, allowing corruption of host kernel shadow pages and breaking guest-host isolation. The issue affects both Intel and AMD hosts; on Intel, exploitation requires that EPT page walk lengths 4 and 5 are both exposed to the L1 guest, while no equivalent constraint was noted for AMD.
The disclosure warns that systems running untrusted guests with nested virtualization enabled are at particular risk, including multi-tenant x86 public cloud environments. Hyunwoo Kim reported the bug to the Linux kernel security team, and the issue has been patched in mainline Linux. The affected range spans from commit f95eec9bed76 through 2abd5287f083, covering code introduced in 2020 and remaining exposed until the July 2026 fix referenced on kernel.org.
