CVE-2026-62430
Deferred Deferred - Pending Action

Xen CMOS Memory Index Race Condition Vulnerability

Publication date: 2026-07-28

Last updated on: 2026-07-28

Assigner: Xen Project

Description
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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Meta Information

Published
2026-07-28
Last Modified
2026-07-28
Generated
2026-08-17
AI Q&A
2026-07-28
EPSS Evaluated
2026-08-16
NVD
CVE-2026-62430
EUVD
EUVD-2026-49783

Affected Vendors & Products

Showing 1 associated CPE
Vendor Product Version / Range
xen xen From 3.2.0 (inc)

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Exploitability

CWE
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KEV
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CWE ID Description
CWE-362 The product contains a concurrent code sequence that requires temporary, exclusive access to a shared resource, but a timing window exists in which the shared resource can be modified by another code sequence operating concurrently.

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Executive Summary

This vulnerability involves an out-of-bounds read in Xen's vRTC emulation due to improper locking when accessing CMOS memory contents. Xen caches a guest-chosen index for memory access but fails to lock it properly, allowing a guest to modify the index after validation. This can lead to reading beyond the intended memory array bounds.

Detection Guidance

Detection requires checking Xen version and configuration. Run 'xl info | grep xen_version' to verify Xen version. Check guest types with 'xl list -v' to confirm PV or PVH guests. No direct commands detect the vulnerability itself, but version checks and guest type verification are necessary steps.

Impact Analysis

The vulnerability could allow a guest to read Xen's internal data, though it does not expose data from other guests. This may lead to information leaks or crashes in the Xen hypervisor, potentially affecting system stability and security.

Compliance Impact

This vulnerability does not directly affect compliance with GDPR or HIPAA as it involves an out-of-bounds read in Xen's vRTC emulation, which does not expose other guests' data or sensitive information. Compliance impact would depend on system configuration and data handling practices rather than the vulnerability itself.

Mitigation Strategies

Immediately upgrade Xen to a patched version (4.19.x, 4.18.x, or 4.17.x). Ensure all guests are PV or PVH type. Apply the patch from XSA-503 advisory. Avoid HVM guests until patched. Monitor Xen security advisories for updates.

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