CVE-2026-42490
Official description Straight from the sourceThe vendor's or NVD's own wording, published unedited. Authoritative, but often terse — it says what broke, rarely what to do.
NVD · unedited[This CNA information record relates to multiple CVEs; the text explains which aspects/vulnerabilities correspond to which CVE.] To create and manage guests, domctl operations are used by the control domain, a possible Xenstore domain, or by a domain controlling a particular guest. Some of these operations may not be executed in parallel, so a system-wide lock is used. The way that lock is acquired is, however, not providing any fairness. This is CVE-2026-42489. Furthermore, with XSM/Flask in use, the lock acquire will, for some operations, occur ahead of any permission checking. This is CVE-2026-42490.
Technical summary Written by usOur analysis, written from the advisory, the CVSS vector and the affected-version data. It adds context the advisory leaves out, and never invents facts that are not in the source.
dbcve analysis · high confidenceIn Xen hypervisor, when XSM/Flask (Xen Security Module/FLASK) is enabled, certain domctl operations used for guest management acquire a system-wide lock before performing permission checks. This ordering issue allows lock acquisition to proceed without proper authorization, potentially enabling unauthorized guest control operations.
Verify against the referenced sources before acting — the references below are authoritative for this CVE, this summary is not.
CVSS breakdown How the score is builtThe industry scoring standard. It rates how the flaw is reached, what it takes to exploit, and what an attacker gains — the score is derived from those, not the other way round.
From the vector- Attack vector
- Network
- Complexity
- Low
- Privileges
- Low
- User interaction
- None
- Scope
- Unchanged
- Confidentiality
- None
- Integrity
- None
- Availability
- High
CVSS:3.1/AV:N/AC:L/PR:L/UI:N/S:U/C:N/I:N/A:H
Am I affected? How to checkSteps we derive from the advisory and the affected-version data, so you can decide whether this CVE reaches your setup. They are a guide, not a scan — your own configuration is the authority.
dbcve checksWork through these to decide whether this CVE applies to you.
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Verify XSM/Flask is enabledCheck the Xen boot parameters or configuration: xl dmesg | grep -i flask or cat /boot/config-$(uname -r) | grep CONFIG_XSM_FLASK, or examine the Xen command line in /boot/grub/grub.cfg for flask=1Affected if XSM/Flask is present and enabled (flask=1 or flask=enforcing in boot params)
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Confirm domctl access control statusRun: xl list -Z or xm dmesg to check if XSM policies are loaded and activeAffected if XSM/Flask policies are actively enforcing access controls on domctl operations
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Review Flask audit logs for lock acquisition eventsCheck /var/log/xen/audit.log or run: xl dmesg | grep -i 'avc: denied' to look for any permission-related denials during domctl operationsAffected if Audit logs show denials or errors related to domctl operations acquiring system-wide locks without proper authorization
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Check Xen hypervisor versionRun: xl version or uname -r to obtain the installed Xen version, then compare against vendor security advisories for CVE-2026-42490Affected if The installed Xen version matches a version affected by CVE-2026-42490 as listed in vendor advisories
You are affected if XSM/Flask is enabled and your Xen version is among those impacted by CVE-2026-42490; if XSM/Flask is disabled, this specific ordering vulnerability does not apply to your environment.
Generated from the published advisory. Verify against your own configuration.
Remediation Closing itWhat it takes to close this. Where a vendor fix exists we point at it; where none exists we say so plainly, and can build one. Effort estimates are scoped from the advisory, not from your codebase.
From vendor dataIf XSM/Flask is not required, disable it. Otherwise, apply vendor patches when available to ensure permission checks occur before lock acquisition in affected domctl operations.
- Consultation6.0 h
- Implementation12.0 h
- Testing8.0 h
- Review / QA6.0 h
An estimate, not a bill — we confirm scope with you before any work starts. Need it this week? Rush from $9,024.
Scan for this in your stack
Free · runs locallyCheck whether your project pulls in CVE-2026-42490 — or any other known-vulnerable package — straight from your lock files. Free and open source; it runs locally and uploads nothing.
References Go to the primary sourcePrimary sources — vendor advisories, patches and trackers. Where our summary and a reference disagree, the reference wins.
Primary sourcesPractitioner notes
ContributedPeer-ranked notes from engineers who’ve handled CVE-2026-42490 in production — separate from our analysis above.
The advisory tells you what broke. It rarely tells you what actually worked. If you’ve dealt with this one, that detail is what the next engineer is searching for.
- The version that genuinely resolved it — not the one the vendor claimed
- A config change or rule that shut the vector down
- A gotcha in the upgrade path that cost you an afternoon
No notes yet
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- Verified mitigations, workarounds, and config changes
- Version or environment caveats, and links to real fixes
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