Zapscape (CVE-2026-64561): A Six-Year-Old KVM/x86 Shadow-MMU Use-After-Free Gives Guest-to-Host Root

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Hyunwoo Kim (@v4bel) published a working exploit on August 6, 2026 after the embargo lifted on oss-security: a use-after-free in KVM/x86's recursive zap path during shadow page reclamation, triggerable entirely from guest-side actions, yielding kernel-privilege command execution on the host. The affected window runs from commit f95eec9bed76 (July 8, 2020) to 2abd5287f083 (July 21, 2026) — just over six years of Linux kernels. It also works as local privilege escalation anywhere /dev/kvm is world-writable, which is directly relevant to anyone running untrusted agent code in KVM-backed sandboxes or multi-tenant CI runners.