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Race ConditionWeakness · CWE-362

CVE-2026-42487

HIGH · 7.9 CVSS v3.1 Published 2026-06-18
Mitigation only
No fix yet — a mitigation exists. There is no fixed release. A documented workaround reduces exposure in the meantime.
See remediation →
81/100
Remediation priority · High
Zero-click

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
HVM guest I/O port accesses are subject to either emulation or at least translation. Translations are managed by the device model (via XEN_DOMCTL_ioport_mapping), and hence the linked list used may changed at any time. Traversal of those lists (while handling guest I/O port accesses) therefore needs synchronizing with updates, which was missing so far.

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 · moderate confidence

A race condition vulnerability exists in the Xen hypervisor where traversal of I/O port translation linked lists during HVM guest I/O port access does not synchronize with concurrent list updates managed via XEN_DOMCTL_ioport_mapping. This missing synchronization could allow an attacker to manipulate the linked list structure during traversal, potentially leading to memory corruption or hypervisor compromise.

MitigationApply the Xen hypervisor patch to add proper synchronization around I/O port mapping list traversal. Until the patch is available, minimize the attack surface by limiting which VMs have I/O port mapping privileges and monitoring for unusual hypervisor activity.

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
Local
Complexity
Low
Privileges
Low
User interaction
None
Scope
Changed
Confidentiality
Low
Integrity
Low
Availability
High

CVSS:3.1/AV:L/AC:L/PR:L/UI:N/S:C/C:L/I:L/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 checks

Work through these to decide whether this CVE applies to you.

  1. Verify Xen hypervisor is in use
    Check the running hypervisor by examining /proc/xen or using 'xl list' or 'xm list' commands to list running domains
    Affected if The system is running the Xen hypervisor and has HVM guest domains active
  2. Check Xen hypervisor version
    Run 'xl info' or 'xm info' to display hypervisor version information, then compare the version number against the fixed version once released
    Affected if The installed Xen version has not yet received the patch for this race condition
  3. Identify HVM guest domains
    Use 'xl list' or 'xm list' and look for domains with type 'HVM' in the output, or check domain configuration files for 'builder = "hvm"'
    Affected if HVM (Hardware Virtual Machine) guests are running, as these perform I/O port access that triggers the vulnerable code path
  4. Check for active I/O port mappings
    Examine domain configuration for any 'ioport_mask' or ioport mapping settings, or use hypervisor debug interfaces to list current ioport mappings managed via XEN_DOMCTL_ioport_mapping
    Affected if The hypervisor has active I/O port mappings configured for domains, as the race condition occurs during traversal of these mapped lists
  5. Monitor for XEN_DOMCTL_ioport_mapping hypercall activity
    Use hypervisor trace buffers or enable debugging for the domctl hypercall path to observe XEN_DOMCTL_ioport_mapping operations occurring concurrently with guest I/O port access
    Affected if Concurrent operations are observed: guest I/O port access happening simultaneously with XEN_DOMCTL_ioport_mapping list updates

A system is affected if it runs an unpatched Xen hypervisor version with HVM guests that have active I/O port mappings configured via XEN_DOMCTL_ioport_mapping, as the race condition requires both the vulnerable traversal code and concurrent list modification operations to occur.

Generated from the published advisory. Verify against your own configuration.

Check your environment

Paste your version and any relevant configuration and it will be compared against the affected criteria above. Do not include secrets or credentials.

AI-assisted, checked against the advisory. Informational, not a guarantee.

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 data
Mitigation available No clean upgrade yet — mitigate in the meantime
Mitigation

Apply the Xen hypervisor patch to add proper synchronization around I/O port mapping list traversal. Until the patch is available, minimize the attack surface by limiting which VMs have I/O port mapping privileges and monitoring for unusual hypervisor activity.

Have this fixed Scoped from the published advisory
  • Consultation6.0 h
  • Implementation16.0 h
  • Testing16.0 h
  • Review / QA8.0 h
46.0 hours of engineering $7,920
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References Go to the primary sourcePrimary sources — vendor advisories, patches and trackers. Where our summary and a reference disagree, the reference wins.

Primary sources

Practitioner notes

Contributed

Peer-ranked notes from engineers who’ve handled CVE-2026-42487 in production — separate from our analysis above.

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What this is

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