CVE-2026-23557

Host administration denial via transactional watch reset

Published May 19, 2026 · Updated May 19, 2026

Reachable assertion in Xen 4.2 and later allows guest OS users to crash C xenstored by sending XS_RESET_WATCHES in a transaction. The C Xenstore daemon accepts the command during an active transaction and reaches an assertion instead of rejecting the invalid state. Any unprivileged domain can stop Xenstore actions and further host domain administration when C xenstored or xenstore-stubdom lacks NDEBUG; oxenstored and NDEBUG builds are unaffected.

CVSS severity6.5
Medium
EPSS probability0.16%
Next 30 days · Sep 16, 2026
Known exploitationUnconfirmed
Based on sourced intelligence
Hinoki checkNot available
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Summary

What happened

Reachable assertion in Xen 4.2 and later allows guest OS users to crash C xenstored by sending XS_RESET_WATCHES in a transaction. The C Xenstore daemon accepts the command during an active transaction and reaches an assertion instead of rejecting the invalid state. Any unprivileged domain can stop Xenstore actions and further host domain administration when C xenstored or xenstore-stubdom lacks NDEBUG; oxenstored and NDEBUG builds are unaffected.

The record

CVE
CVE-2026-23557
Published
May 19, 2026
Updated
May 19, 2026
Vendor
Unknown vendor
Product
Unknown product
Classifications
CWE-617, T1499.004
Attack vector
local
Privileges
authenticated

Timeline

How it unfolded

  1. May 19, 2026CVE publishedPublication date reported by the CVE source.
  2. May 19, 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?

Affected buildAffected product and version details are unavailable.

What conditions does exploitation require?

Attack vectorlocal
Required privilegesauthenticated

What is affected?

Affected products and versions are unavailable in this record.

Published CVSS scores

6.5CISA-ADPCVSS:3.1/AV:L/AC:L/PR:L/UI:N/S:C/C:N/I:N/A: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
Privilegesauthenticated
Known exploitationUnconfirmed
Public exploitUnconfirmed

Weakness, pattern, technique

CWE-617Reachable Assertion
T1499.004Application or System Exploitation

Public exploit references

No public exploit references are available in this record.

Labels summarize the accepted research assessment. They do not indicate a test against your environment.

Technologies

Your stack

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Your stack

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