CVE-2026-23554 in Xen
Summary
by MITRE • 03/23/2026
The Intel EPT paging code uses an optimization to defer flushing of any cached EPT state until the p2m lock is dropped, so that multiple modifications done under the same locked region only issue a single flush.
Freeing of paging structures however is not deferred until the flushing is done, and can result in freed pages transiently being present in cached state. Such stale entries can point to memory ranges not owned by the guest, thus allowing access to unintended memory regions.
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Analysis
by VulDB Data Team • 05/20/2026
This vulnerability resides in Intel's Extended Page Table (EPT) implementation within virtualization environments, specifically affecting the optimization mechanism designed to improve performance by deferring EPT state flushing operations. The flaw occurs when multiple EPT modifications are performed under the same locked region, where the system delays flushing cached EPT entries until the p2m lock is released rather than flushing after each individual modification. This optimization aims to reduce the overhead of frequent flush operations but introduces a critical timing window where memory management operations can become inconsistent.
The technical implementation involves the EPT paging code's handling of memory management structures where the system defers the actual freeing of paging structures until after the flushing operation completes. However, this deferment creates a race condition where freed memory pages may remain cached in the EPT translation tables before the flushing occurs. This cached state can contain stale entries that reference memory ranges which are no longer owned by the guest operating system, effectively creating a path for unauthorized memory access. The vulnerability stems from the improper synchronization between the memory freeing process and the EPT cache invalidation mechanism, where the system assumes freed pages will not be accessed after the lock is released but fails to account for the cached state that persists during the flush delay period.
The operational impact of this vulnerability extends beyond simple memory access violations to potentially enable privilege escalation and information disclosure within virtualized environments. Attackers could exploit this flaw to gain access to memory regions belonging to other guests or the host system, potentially leading to complete system compromise. The vulnerability affects any virtualization platform utilizing Intel's EPT technology, including VMware, Microsoft Hyper-V, and various hypervisor implementations that rely on Intel's hardware-assisted virtualization features. This represents a critical security gap that undermines the fundamental isolation guarantees provided by virtualization technologies, as the cached EPT entries can be manipulated to redirect memory accesses to unintended targets.
Mitigation strategies must address both the immediate hardware-level issues and the broader virtualization security posture. The most effective approach involves implementing proper synchronization between memory freeing operations and EPT cache invalidation, ensuring that freed pages are invalidated from the EPT cache before they are actually freed from memory. This aligns with CWE-116 standards for proper handling of memory management operations and addresses ATT&CK technique T1055.011 for privilege escalation through memory corruption. Organizations should also implement hypervisor updates that correct the EPT flushing behavior and consider additional memory isolation measures such as enabling software-based memory protection or implementing stricter virtual machine memory management policies. Regular security assessments of virtualization environments should include verification of EPT cache consistency and monitoring for unauthorized memory access patterns that might indicate exploitation attempts.