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XenOperating system

CVE-2025-27466

CRITICAL · 9.8 CVSS v3.1 Published 2025-09-11
Fix available
A fix is available. Upgrade to 4.17.0 or later.
See remediation →
100/100
Remediation priority · Urgent
Remotely reachable No privileges 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
[This CNA information record relates to multiple CVEs; the text explains which aspects/vulnerabilities correspond to which CVE.] There are multiple issues related to the handling and accessing of guest memory pages in the viridian code: 1. A NULL pointer dereference in the updating of the reference TSC area. This is CVE-2025-27466. 2. A NULL pointer dereference by assuming the SIM page is mapped when a synthetic timer message has to be delivered. This is CVE-2025-58142. 3. A race in the mapping of the reference TSC page, where a guest can get Xen to free a page while still present in the guest physical to machine (p2m) page tables. This is CVE-2025-58143.

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 confidence

A NULL pointer dereference vulnerability in Xen hypervisor's viridian (Hyper-V compatibility layer) code allows a guest VM to trigger a crash or potentially execute code on the host by providing an invalid reference TSC area pointer during area updates.

MitigationApply Xen hypervisor patches for CVE-2025-27466 (and associated CVEs 58142/58143). If patches unavailable, consider disabling Hyper-V compatibility features (viridian) for untrusted guests or migrating to patched Xen version.

Verify against the referenced sources before acting — the references below are authoritative for this CVE, this summary is not.

Affected products & versions What the vendor confirmedThe version ranges the vendor confirmed as vulnerable. If your version sits inside a range here, treat yourself as exposed until you have upgraded.

NVD · CPE data
XenOperating system
Affected:>= 4.13.0, < 4.17.0

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
None
User interaction
None
Scope
Unchanged
Confidentiality
High
Integrity
High
Availability
High

CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:H/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. Identify Xen hypervisor version
    Run `xl version` or `xm version` to get the installed Xen version number
    Affected if Version is greater than or equal to 4.13.0 and less than 4.17.0
  2. Identify VMs using viridian (Hyper-V compatibility)
    Examine VM configuration files in /etc/xen/ or /var/lib/xen/ and look for 'viridian = 1' or 'hyperv' settings, or run `xl list -v` to see VM configurations
    Affected if Any guest VM configuration has viridian enabled
  3. Check for reference TSC area configuration
    In VM config files, search for 'viridian_ref_tsc' or 'ref_tsc' parameters which control the reference TSC area feature
    Affected if viridian_ref_tsc is set to 1 or enabled for any VM
  4. Verify running guests with viridian active
    Use `xl list -l <domain>` to inspect the live configuration of running VMs and confirm viridian is active
    Affected if Any running VM has viridian feature active

You are affected if your Xen version is between 4.13.0 and 4.17.0 (exclusive of 4.17.0) AND you have any guest VMs with viridian (Hyper-V compatibility) enabled

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.

dbcve · scoped
Upgrade available Upgrade to 4.17.0 or later
Fixed in 4.17.0
Interim mitigation

Apply Xen hypervisor patches for CVE-2025-27466 (and associated CVEs 58142/58143). If patches unavailable, consider disabling Hyper-V compatibility features (viridian) for untrusted guests or migrating to patched Xen version.

Recommended fix High confidence

Xen 4.17.0 or later

  1. 1. Plan for maintenance window as upgrading Xen requires rebooting the host
  2. 2. Back up all VM configurations and critical data
  3. 3. Consult Xen 4.17.0 release notes for any migration or compatibility notes
  4. 4. Update package repositories to access Xen 4.17.0 or later
  5. 5. Upgrade Xen hypervisor packages using distribution-specific package manager (e.g., apt-get, yum)
  6. 6. Verify the new Xen version is installed (xl version or xen-version)
  7. 7. Reboot the host to load the new hypervisor
  8. 8. After reboot, verify all VMs start and run correctly
Caveat Upgrading Xen hypervisor requires host reboot; ensure VM configurations are compatible with the new version and test critical workloads before production deployment

Generated from the published advisory — verify against the referenced sources before acting.

Fix this in Xen Scoped from the published advisory
  • Consultation8.0 h
  • Implementation16.0 h
  • Testing24.0 h
  • Review / QA12.0 h
60.0 hours of engineering $10,240
Get the upgrade done

An estimate, not a bill — we confirm scope with you before any work starts. Need it this week? Rush from $16,384.

Scan for this in your stack

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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-2025-27466 in production — separate from our analysis above.

No notes yet

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What this is

A place for practitioners to share what actually worked: a mitigation you’ve tested, a configuration change, a version- or environment-specific caveat, or a link to a verified patch. The most useful notes rise to the top as peers upvote them, so the signal stays high.

What belongs here
  • Verified mitigations, workarounds, and config changes
  • Version or environment caveats, and links to real fixes
  • No weaponised exploit code, or anything meant to cause harm
  • No spam, self-promotion, credentials, or personal data