CVE-2025-58151

Guest-to-host code execution via shared-buffer TOCTOU

Published Jul 9, 2026 · Updated Jul 9, 2026

A TOCTOU race in all versions of Xen varstored allows guest OS users with kernel access to execute code in the host-side daemon. Insufficient compiler barriers let OVMF-controlled shared-buffer fields be re-read after validation; default builds can use the changed value as a jump-table index. Only Xapi systems with x86 HVM guests configured for UEFI are exposed; PV guests and HVM guests using BIOS cannot reach the flaw.

CVSS severity9.4
Critical
EPSS probability0.14%
Next 30 days · Sep 16, 2026
Known exploitationUnconfirmed
Based on sourced intelligence
Hinoki checkNot available
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Summary

What happened

A TOCTOU race in all versions of Xen varstored allows guest OS users with kernel access to execute code in the host-side daemon. Insufficient compiler barriers let OVMF-controlled shared-buffer fields be re-read after validation; default builds can use the changed value as a jump-table index. Only Xapi systems with x86 HVM guests configured for UEFI are exposed; PV guests and HVM guests using BIOS cannot reach the flaw.

The record

CVE
CVE-2025-58151
Published
Jul 9, 2026
Updated
Jul 9, 2026
Vendor
Xen Project
Product
varstored
Classifications
CWE-367, T1611
Attack vector
local
Privileges
admin

Timeline

How it unfolded

  1. Jul 9, 2026CVE publishedPublication date reported by the CVE source.
  2. Jul 9, 2026Record updatedLatest update available in the CVE record.

Exploitability

Present is not the same as exploitable

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Is a vulnerable build present?

Compare these published version ranges with your installed build and any vendor patches.

  1. Affected versionversion=all

What conditions does exploitation require?

Attack vectorlocal
Required privilegesadmin

What is affected?

Xen Project · varstoredversion=all

Published CVSS scores

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

CVSS describes severity. EPSS estimates exploitation probability.

Attacks

What attackers are doing with it

Daily unique IPs observed by Shadowserver honeypots for known exploited vulnerabilities (KEVs). Missing observations do not establish an absence of attacks.

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No observations available

Sep 10, 2026Sep 16, 2026
Latest reporting daySep 16, 2026
Latest daily unique IPsUnavailable
Prior 30-day averageUnavailable
SourceShadowserver honeypots (KEV)
Vectorlocal
Privilegesadmin
Known exploitationUnconfirmed
Public exploitUnconfirmed

Weakness, pattern, technique

CWE-367Time-of-check Time-of-use (TOCTOU) Race Condition
T1611Escape to Host

Public exploit references

No public exploit references are available in this record.

Labels summarize the accepted research assessment. They do not indicate a test against your environment.

Technologies

Your stack

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Your stack

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