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

Summary: Researcher Hyunwoo Kim disclosed Zapscape, tracked as CVE-2026-64561, a KVM/x86 shadow-MMU flaw in which a stale-root check ordering error can lead to a use-after-free and let an attacker with L1 guest kernel privileges escape KVM isolation and run commands on the host as root. The upstream fix, commit 2abd5287f083, moves the stale-root check after make_mmu_pages_available(); the National Vulnerability Database lists Linux 5.9 and later as affected until fixed releases including 6.6.148, 6.12.101, 6.18.42, 7.1.6, and 7.2-rc5, and Red Hat assigned a preliminary CVSS score of 7.0.
Key Takeaway: The exposure is conditional but concrete: hosts that expose nested virtualization to untrusted guests, where guest root is the starting point, and Kim's public proof-of-concept creates a root-owned file named /Zapscape on a vulnerable host. As of August 6, 2026, Debian's tracker still listed bullseye, bookworm, and trixie kernel packages, including their security repositories, as vulnerable.

Read the original at The Hacker News ↗

Topics: Vulnerabilities & Patching
Mentions: CVE-2026-64561
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