KVM Shadow Paging Use-After-Free Exposes x86 Hosts to Guest-Triggered Memory Corruption

A use-after-free vulnerability in KVM's shadow paging code was disclosed after researchers Alexander Bulekov and Fred Griffoul of Amazon found stale reverse mappings in shadow EPT through fuzzing. The flaw affects x86 guests and is exploitable when nested virtualization is enabled on Intel or AMD processors, or when systems use shadow paging with EPT or NPT disabled. Maintainers said the bug can lead to kernel memory corruption and denial of service on the host, making it a guest-to-host risk in affected virtualization setups.

The disclosure was coordinated by Sandipan Roy, who said reporters and maintainers agreed to an embargo that ended on March 29, 2026 at 16:00 UTC. Solar Designer said the issue had first been shared with the linux-distros list on March 10, 2026 and acknowledged the embargo exceeded that list's usual 14-day limit without prior approval, though it was allowed because the overrun was moderate and multiple stakeholders were already involved. The discussion also noted that on Linux kernels 6.16 and newer, the reproducer hits a WARN introduced by commit 11d45175111d, raising questions about whether panic_on_warn could reduce exploitability.