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CWE-281Weakness · CWE-281

CVE-2026-23556

CRITICAL · 9.4 CVSS v4.0 Published 2026-07-09
Mitigation only
No fix yet — a mitigation exists. There is no fixed release. A documented workaround reduces exposure in the meantime.
See remediation →
99/100
Remediation priority · Urgent
No privileges Zero-click 6 weeks old

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
When oxenstored is tearing a domain down, the node data is cleaned up but the usage counts are leaked. When the domain ID is eventually reused, the new domain can create fewer nodes before beeing deemed to be over quota.

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

In Xen oxenstored, when a domain is destroyed, the node data is cleaned up but the usage count (quota accounting) is not decremented. When the domain ID is reused, the new domain inherits the leaked usage counts, causing it to hit quota limits prematurely with fewer nodes than expected.

MitigationApply the vendor patch to oxenstored to ensure usage counts are properly cleaned up when domains are torn down. Monitor for unexpected quotaExceeded errors on domains with recently reused IDs as a temporary indicator.

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
None
Authentication
X
User interaction
None
Scope
X

CVSS:4.0/AV:L/AC:L/AT:N/PR:N/UI:N/VC:H/VI:H/VA:H/SC:H/SI:H/SA:H/E:X/CR:X/IR:X/AR:X/MAV:X/MAC:X/MAT:X/MPR:X/MUI:X/MVC:X/MVI:X/MVA:X/MSC:X/MSI:X/MSA:X/S:X/AU:X/R:X/V:X/RE:X/U:X

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 if oxenstored is the storage backend in use
    Check the Xen configuration (typically in /etc/xen/xen-hotplug-common.sh or xl.conf) for the presence of 'oxenstored' or the variable OXS=/usr/bin/oxenstored. Alternatively, run 'ps aux | grep oxenstored' to see if the oxenstored process is running.
    Affected if oxenstored is confirmed to be running as the storage daemon
  2. Check the oxenstored version
    Run 'oxenstored --version' or check the package version with 'rpm -q oxenstored' or 'dpkg -l oxenstored' depending on your distribution.
    Affected if The installed version is older than the patched version that fixes this issue (compare your installed version to the fixed version provided by your Xen vendor)
  3. Verify quota tracking is enabled
    Examine the oxenstored configuration file (typically /etc/xen/oxenstored.conf or /etc/xen/xl.conf) for quota-related settings such as 'quota-maxnodecount', 'quota-maxsocketcount', or 'quota-maxgrantcount'. Also check if these quotas are actively enforced.
    Affected if Quota tracking is enabled and enforced in the configuration
  4. Check for domain ID reuse with quota errors
    Monitor Xen domain logs (xl dmesg or /var/log/xen/dom0-logs) for patterns where domain IDs are being reused (new domains starting with IDs that were previously destroyed) and correlate with quotaExceeded or quota-related error messages.
    Affected if Domain IDs have been reused after domain destruction AND unexpected quota limit errors occur on the new domain with that ID
  5. Inspect active domain IDs for potential quota leakage
    Use 'xl list' to view all active domains and note the domain IDs in use. Cross-reference with any historical domain ID records to identify IDs that were previously assigned to destroyed domains and are now reused.
    Affected if Domain ID reuse is occurring in the environment

If oxenstored is in use with quota tracking enabled and domain IDs have been reused after domain destruction, the environment may be affected by this quota leakage issue.

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 vendor patch to oxenstored to ensure usage counts are properly cleaned up when domains are torn down. Monitor for unexpected quotaExceeded errors on domains with recently reused IDs as a temporary indicator.

Have this fixed Scoped from the published advisory
  • Consultation4.0 h
  • Implementation12.0 h
  • Testing10.0 h
  • Review / QA6.0 h
32.0 hours of engineering $5,540
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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-2026-23556 in production — separate from our analysis above.

No notes yet

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What this is

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What belongs here
  • Verified mitigations, workarounds, and config changes
  • Version or environment caveats, and links to real fixes
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