CVE-2026-62430: x86: Out-of-bounds read in vRTC emulation

Severity: high (CVSS 7.5 v3.1)
Exploited in the wild: not listed in CISA KEV
EPSS: 0.2% probability of exploitation in the next 30 days
Public exploit or detection template: none known
Published: 2026-07-28 · updated 2026-07-28
Weakness: CWE-362

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.

References

https://xenbits.xenproject.org/xsa/advisory-503.html
http://www.openwall.com/lists/oss-security/2026/07/28/19
http://xenbits.xen.org/xsa/advisory-503.html

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