CVE-2026-62430 in Xen
Summary
by MITRE • 07/28/2026
Accesses to the CMOS memory contents are done using an indirect IO port pair. Therefore Xen needs to cache the guest chosen index, and one of the usages of the index didn't take the necessary locking to avoid concurrent changes. As a result, a guest could change the index after it being checked, causing a subsequent out-of-bound read access to the contents of an array.
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Analysis
by VulDB Data Team • 07/28/2026
This vulnerability resides within the hypervisor's implementation of CMOS memory access mechanisms in virtualized environments. The core issue stems from improper synchronization when handling indirect IO port operations that access CMOS memory regions. Xen maintains a cached copy of the guest-selected index value to facilitate these memory operations, but fails to implement adequate locking mechanisms during certain usage scenarios. The flaw manifests when the hypervisor performs an initial check on the cached index value, only to have the guest subsequently modify this same index before the operation completes. This race condition creates a scenario where the hypervisor proceeds with array access using an outdated index that may reference memory locations outside the intended bounds.
The technical exploitation of this vulnerability involves a timing attack pattern where malicious guest code deliberately manipulates the CMOS index register between the validation check and actual memory access phase. This creates an out-of-bounds read condition that could potentially expose sensitive data from adjacent memory regions within the hypervisor's memory space. The vulnerability directly relates to CWE-367, which addresses time-of-check to time-of-use security flaws, where the state of a resource changes between verification and actual usage. The implications extend beyond simple information disclosure, as this flaw could enable attackers to access hypervisor internal structures or other guest memory regions, potentially leading to privilege escalation or complete system compromise.
From an operational perspective, this vulnerability represents a critical security weakness in virtualization environments where multiple guests share the same physical host. Attackers could leverage this flaw to bypass isolation mechanisms between virtual machines, accessing data that should remain compartmentalized within separate guest instances. The impact is particularly severe in cloud computing and multi-tenant environments where hypervisor-level vulnerabilities can affect entire infrastructure deployments. This vulnerability aligns with several ATT&CK techniques including privilege escalation through hypervisor attacks and credential access via memory manipulation. The flaw demonstrates inadequate concurrency control in hypervisor kernel components, specifically affecting the CMOS emulation layer that handles hardware abstraction for virtualized systems.
Mitigation strategies should focus on implementing proper locking mechanisms around the cached index access operations within the Xen hypervisor codebase. The most effective approach involves adding appropriate mutex or spinlock protection during the critical section where the index value is checked and subsequently used for array access. Additionally, defensive programming measures such as input validation and bounds checking should be strengthened to prevent any potential out-of-bounds memory accesses even if race conditions occur. System administrators should ensure Xen hypervisor versions include patches addressing this specific vulnerability, while also implementing monitoring for suspicious CMOS access patterns that could indicate exploitation attempts. The fix must be carefully implemented to maintain performance characteristics while ensuring thread safety across all concurrent access scenarios involving the CMOS memory interface.