Agent receiver accepts mTLS requests without a client certificate (CVE-2026-15576) | HOL Guard CVE

Unknown severity · Source severity not reportedCVE-2026-15576

Agent receiver accepts mTLS requests without a client certificate

Answer in brief

CVE-2026-15576 records a Unknown severity vulnerability in Agent receiver accepts mTLS requests without a client certificate. The current sources do not mark it as known exploited. The current feed maps Checkmk GmbH/Checkmk (generic). Check affected ranges and fixed versions before updating.

Analysis pending evidence review

HOL Guard separates source facts from reviewed analysis. See the methodology.

Published Aug 21, 2026Updated Aug 21, 2026Source checked Aug 21, 2026First seen by HOL Aug 21, 2026Material review Aug 21, 2026

Upstream Advisory

Key facts

Risk: Unknown severitySource severity not reported
Exploitation: Not marked as known exploited
Affected software: 1 mapped package or product
Fix availability: Available

Why this deserves its current priority

A CVSS score is not reported in the current record. The current sources do not mark it as known exploited. Treat this as a source-backed prioritization signal, not a statement about your environment.

Analysis status

Analysis pending evidence review

Factual feed record only; HOL analysis is not approved for indexing. Read the methodology.

Affected scope and exposure questions

The current feed maps Checkmk GmbH/Checkmk (generic). Check affected ranges and fixed versions before updating.

Mapped affected packages and fixed versions
Package	Affected range	Fixed version
Checkmk GmbH/Checkmkgeneric	>=2.5.0 <2.5.0p10	2.5.0p10

Recommended response

Check inventory. Check lockfiles and deployed manifests for Checkmk GmbH/Checkmk.
Review the reported fix. Update Checkmk GmbH/Checkmk to 2.5.0p10 if you use the affected versions. Test the change in a non-production environment first.

Evidence timeline and material changes

Published upstream
Aug 21, 2026
Evidence: source:cvelist:source_dates:source-dates:record
Source modified
Aug 21, 2026
Evidence: source:cvelist:source_dates:source-dates:record
First seen by HOL
Aug 21, 2026

Sources and claim methodology

Source referencecheckmk.com

Upstream source description

Improper authentication in the agent receiver of Checkmk <2.5.0p10 allows an unauthenticated remote attacker to bypass mutual TLS client certificate verification of relay endpoints by supplying a fixed placeholder identity in the request URL, resulting in limited impact on integrity and availability. Only the Cloud, Ultimate and Ultimate MT editions are affected, as other editions do not expose relay endpoints.

Quoted source text, attributed separately from HOL analysis.