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Description

varstored is a component of the Xapi toolstack handling UEFI Variables for a VM. It has a communication path with OVMF inside the VM involving mapping a buffer prepared by OVMF. Within varstored, there were insufficient compiler barriers, creating TOCTOU issues with data in the shared buffer. The exact vulnerable behaviour depends on the code generated by the compiler. In a build of varstored using default settings, the attacker can control an index used in a jump table.

PUBLISHED Reserved 2025-08-26 | Published 2026-07-09 | Updated 2026-07-09 | Assigner XEN




CRITICAL: 9.4CVSS:4.0/AV:L/AC:L/AT:N/PR:N/UI:N/VC:H/VI:H/VA:H/SC:H/SI:H/SA:H

Problem types

CWE-367 Time-of-check time-of-use (TOCTOU) race condition

Product status

Default status
unaffected

all
affected

Credits

This issue was discovered by Teddy Astie of Vates. finder

References

www.openwall.com/lists/oss-security/2026/01/27/2

xenbits.xen.org/xsa/advisory-478.html

xenbits.xen.org/xsa/advisory-478.html

cve.org (CVE-2025-58151)

nvd.nist.gov (CVE-2025-58151)

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