Article URL: https://github.com/V4bel/Zapscape Comments URL: https://news.ycombinator.com/item?id=49198843 Points: 25 # Comments: 4

This document describes the Zapscape (CVE-2026-64561) vulnerability discovered and reported by Hyunwoo Kim (@v4bel). It is a KVM escape vulnerability that lets a guest escape to the host in a KVM/x86 environment and run commands on the host with kernel (root) privilege. Zapscape is a use-after-free vulnerability in the shadow MMU emulation of KVM/x86, specifically in the recursive zap path that runs when shadow pages are reclaimed. It can trigger the bug with guest-side actions alone to corrupt the host kernel's shadow page, and it can threaten the guest-host isolation of KVM/x86 hosts that accept untrusted guests and expose nested virtualization, particularly multi-tenant x86 public clouds. After reporting this vulnerability to linux-distros@vs.openwall.org, the agreed embargo has ended, so the exploit is posted to oss-security and this Zapscape document is published. For the disclosure timeline, see the technical detail document. The PoC is written to target AMD, and for safe testing, running it under QEMU TCG is recommended. The PoC has the following structure. This PoC is not a weaponized exploit that runs immediately in a cloud environment, but demonstration code that reproduces the vulnerability and the full exploit chain on top of QEMU TCG. To use it in a real cloud environment, the L1 actions the PoC performs must be moved into a guest kernel module, and the exploit must be ported to match the host kernel's kconfig. This is not a difficult task. This PoC is intended to provide accurate information. Do not use it on systems you are not authorized to test. Zapscape (CVE-2026-64561) covers the range from f95eec9bed76 (2020-07-08) to 2abd5287f083 (2026-07-21). It occurs in the same shadow MMU, but it is a separate vulnerability with a different root cause.