CVE-2026-23556

Guest service denial via leaked quota accounting

Published Jul 9, 2026 · Updated Jul 9, 2026

Resource exhaustion in Xen Project oxenstored allows guest OS users to deny Xenstore service by exhausting persistent node quotas. During domain teardown, the node cleanup deletes the domain's data but fails to decrement its per-domain node-usage counters before the domain ID is recycled. The host must use OCaml oxenstored with the XSA-419 fixes; repeated quota filling and guest reboots accelerate the leak until new domains cannot operate.

CVSS severity9.4
Critical
EPSS probability0.14%
Next 30 days · Sep 16, 2026
Known exploitationUnconfirmed
Based on sourced intelligence
Hinoki checkNot available
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Summary

What happened

Resource exhaustion in Xen Project oxenstored allows guest OS users to deny Xenstore service by exhausting persistent node quotas. During domain teardown, the node cleanup deletes the domain's data but fails to decrement its per-domain node-usage counters before the domain ID is recycled. The host must use OCaml oxenstored with the XSA-419 fixes; repeated quota filling and guest reboots accelerate the leak until new domains cannot operate.

The record

CVE
CVE-2026-23556
Published
Jul 9, 2026
Updated
Jul 9, 2026
Vendor
Xen Project
Product
oxenstored
Classifications
CWE-281, CAPEC-548, T1499.003
Attack vector
local
Privileges
unauthenticated

Timeline

How it unfolded

  1. Jul 9, 2026CVE publishedPublication date reported by the CVE source.
  2. Jul 9, 2026Record updatedLatest update available in the CVE record.

Exploitability

Present is not the same as exploitable

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Is a vulnerable build present?

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  1. Affected versionversion=all

What conditions does exploitation require?

Attack vectorlocal
Required privilegesunauthenticated

What is affected?

Xen Project · oxenstoredversion=all

Published CVSS scores

9.4Xen Project CNACVSS:4.0/AV:L/AC:L/AT:N/PR:N/UI:N/VC:H/VI:H/VA:H/SC:H/SI:H/SA:H

CVSS describes severity. EPSS estimates exploitation probability.

Attacks

What attackers are doing with it

Daily unique IPs observed by Shadowserver honeypots for known exploited vulnerabilities (KEVs). Missing observations do not establish an absence of attacks.

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No observations available

Sep 10, 2026Sep 16, 2026
Latest reporting daySep 16, 2026
Latest daily unique IPsUnavailable
Prior 30-day averageUnavailable
SourceShadowserver honeypots (KEV)
Vectorlocal
Privilegesunauthenticated
Known exploitationUnconfirmed
Public exploitUnconfirmed

Weakness, pattern, technique

CWE-281Improper Preservation of Permissions
CAPEC-548Contaminate Resource
T1499.003Application Exhaustion Flood

Public exploit references

No public exploit references are available in this record.

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Technologies

Your stack

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Your stack

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