MMU Emulation of Kvm/x86. the Use-after-free Bug, Triggered by Guest-side Actions Alone, Lets a Guest Escape to the Host and Run Commands

The PoC targets AMD and is designed for safe testing under QEMU TCG; it is demonstration code, not a weaponized exploit, but porting it to a real cloud environment is not difficult. The vulnerability affects KVM versions from f95eec9bed76 (2020-07-08) to 2abd5287f083 (2026-07-21). Unlike the similar Januscape (CVE-2026-53359), on Intel it triggers only when both EPT page walk length 4 and 5 are exposed to L1. It requires L1 kernel privilege, which is typically satisfied on public cloud instances.

The embargo ended after reporting to linux-distros@vs.openwall.org, and the exploit was posted to oss-security. Kim recommends establishing a sustainable patching process for host hypervisors.