CVE-2026-15576Network attack vector

Unauthenticated relay access via placeholder identity

Published Aug 21, 2026 · Updated Aug 21, 2026

Improper authentication in Checkmk 2.5.0 before 2.5.0p10 allows remote attackers to access relay endpoints without a client certificate. The agent receiver inserts a fixed placeholder identity when no certificate is presented, so the same value in the request URL satisfies its mTLS identity check. Only Cloud, Ultimate, and Ultimate MT editions expose the relay endpoints; the bypass permits limited integrity and availability effects.

CVSS severity6.9
Medium
EPSS probability0.27%
Next 30 days · Sep 16, 2026
Known exploitationUnconfirmed
Based on sourced intelligence
Hinoki checkNot available
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Summary

What happened

Improper authentication in Checkmk 2.5.0 before 2.5.0p10 allows remote attackers to access relay endpoints without a client certificate. The agent receiver inserts a fixed placeholder identity when no certificate is presented, so the same value in the request URL satisfies its mTLS identity check. Only Cloud, Ultimate, and Ultimate MT editions expose the relay endpoints; the bypass permits limited integrity and availability effects.

The record

CVE
CVE-2026-15576
Published
Aug 21, 2026
Updated
Aug 21, 2026
Vendor
Checkmk GmbH
Product
Checkmk
Classifications
CWE-306, CAPEC-115, T1190
Attack vector
network
Privileges
unauthenticated

Timeline

How it unfolded

  1. Aug 21, 2026CVE publishedPublication date reported by the CVE source.
  2. Aug 21, 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?

Compare these published version ranges with your installed build and any vendor patches.

  1. Affected versionversion=2.5.0 <2.5.0p10

What conditions does exploitation require?

Attack vectornetwork
Required privilegesunauthenticated

What is affected?

Checkmk GmbH · Checkmkversion=2.5.0 <2.5.0p10

Published CVSS scores

6.9Checkmk GmbHCVSS:4.0/AV:N/AC:L/AT:N/PR:N/UI:N/VC:N/VI:L/VA:L/SC:N/SI:N/SA:N

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.

Daily unique IPsNo honeypot observations are available for this CVE in the selected window.

No observations available

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

Weakness, pattern, technique

CWE-306Missing Authentication for Critical Function
CAPEC-115Authentication Bypass
T1190Exploit Public-Facing Application

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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