New Zapscape KVM Flaw Could Let Privileged L1 Guest Code Escape to Linux Hosts

Zapscape, a new Linux kernel vulnerability, could allow an attacker with kernel privileges inside an L1 guest virtual machine (VM) to escape KVM isolation and execute code on the host. The flaw is tracked as CVE-2026-64561 and affects KVM/x86's shadow memory management unit (MMU), which manages shadow page tables used for nested guest memory translation. During guest-triggered page fault handling, KVM can reclaim MMU pages and invalidate the shadow MMU root page still being used by the fault-handling path. Reclaim could then invalidate that same root, but KVM continued the fault path and created child shadow pages under it. If reclaim invalidates the current root, KVM now restarts the fault with RET_PF_RETRY instead of continuing to map or fetch under the invalid root.