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Xen Hypervisor EUVDEUVD-2026-37889

| CVE-2026-42489 MEDIUM
Improper Locking (CWE-667)
2026-06-09 GHSA-vw8q-74w5-57vq
Python Information Disclosure
5.3
CVSS 3.1 · Vendor
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Severity by source

Vendor (CNA) PRIMARY
5.3 MEDIUM
AV:L/AC:H/PR:H/UI:N/S:C/C:N/I:N/A:H
SUSE
MEDIUM
qualitative

Primary rating from Vendor (CNA).

CVSS VectorVendor

CVSS:3.1/AV:L/AC:H/PR:H/UI:N/S:C/C:N/I:N/A:H
Attack Vector
Local
Attack Complexity
High
Privileges Required
High
User Interaction
None
Scope
Changed
Confidentiality
None
Integrity
None
Availability
High

Lifecycle Timeline

3
Severity Changed
Jun 18, 2026 - 19:38 NVD
CRITICAL MEDIUM
CVSS changed
Jun 18, 2026 - 19:38 NVD
5.3 (CRITICAL) 5.3 (MEDIUM)
Analysis Generated
Jun 09, 2026 - 14:17 vuln.today

Description PRE-NVD

Disclosed via oss-security. NVD scoring and full description are pending.

Articles & Coverage 1

News Critical Denial of Service in Python via Xen domctl Lock Abuse - CVE-2026-42489 Jun 09, 2026

AnalysisAI

Denial of service against Xen host management is possible through deliberate abuse of the unfair domctl system-wide lock, affecting all Xen versions from 3.3 onwards. A less-privileged domain can monopolize the lock used to serialize guest creation and management operations, starving the control domain or equally/more-privileged entities of lock access and potentially rendering the entire host unmanageable. No public exploit identified at time of analysis, and no CVSS score was published with XSA-492.

Technical ContextAI

Xen's domctl interface is the primary mechanism through which the control domain, a possible Xenstore domain, or a domain managing a specific guest creates and administers guest VMs. Because certain domctl operations cannot safely execute concurrently, a system-wide lock serializes them. CVE-2026-42489 is specifically the lock fairness deficiency: the acquisition path does not implement any fairness or priority ordering, meaning a lower-privileged domain that aggressively contends for the lock can cause indefinite starvation of higher-priority requestors. This maps to CWE-667 (Improper Locking) / CWE-362 (Concurrent Execution Using Shared Resource with Improper Synchronization). The companion issue CVE-2026-42490 (same XSA-492 advisory) is distinct: when XSM/Flask mandatory access control is in use, lock acquisition occurs before permission checks for some operations, allowing the lock to be held before authorization is verified. No CWE identifier was formally assigned in the advisory data.

Affected ProductsAI

All Xen Hypervisor releases from version 3.3 onwards are confirmed vulnerable per the XSA-492 advisory. Versions prior to 3.3 use a different locking implementation but may also be vulnerable. Patch sets have been released for Xen 4.17.x (18 patches), 4.18.x (19 patches), 4.19.x, 4.20.x, 4.21.x, and xen-unstable. No CPE strings were included in the source data. The Xen Project security policy page is at http://www.xenproject.org/security-policy.html and the full advisory is at https://seclists.org/oss-sec/2026/q2/858.

RemediationAI

Apply the XSA-492 patch set appropriate for the installed Xen branch, available for Xen 4.17.x through 4.21.x and xen-unstable via the Xen Security Advisory at https://seclists.org/oss-sec/2026/q2/858. Downstreams should update to the tip of the relevant stable branch before applying, as patches are prepared against stable branches and may not cleanly apply to release tarballs. Critically, for Xen 4.21 and staging (xen-unstable), the patches include an adjustment to the default XSM/Flask policy; environments running custom Flask policies must manually apply a corresponding policy change or the XSM/Flask permission check bypass (CVE-2026-42490) will remain. No known mitigation exists - the advisory explicitly states 'There is no known mitigation,' so compensating controls such as restricting domctl access via XSM/Flask policies may reduce exposure to CVE-2026-42490 but do not address the CVE-2026-42489 lock fairness flaw itself.

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Vendor StatusVendor

SUSE

Severity: Medium
Product Status
SUSE Linux Enterprise High Performance Computing 15 SP5-ESPOS Affected
SUSE Linux Enterprise High Performance Computing 15 SP5-LTSS Affected
SUSE Linux Enterprise Micro 5.5 Affected
SUSE Linux Enterprise Module for Basesystem 15 SP7 Affected
SUSE Linux Enterprise Server 15 SP7 Affected

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EUVD-2026-37889 vulnerability details – vuln.today
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