OpenNMS XML collector XXE allows arbitrary file read from the OpenNMS host (CVE-2026-19596) | HOL Guard CVE

Unknown severity · Source severity not reportedCVE-2026-19596

OpenNMS XML collector XXE allows arbitrary file read from the OpenNMS host

Answer in brief

CVE-2026-19596 records a Unknown severity vulnerability in OpenNMS XML collector XXE allows arbitrary file read from the OpenNMS host. The current sources do not mark it as known exploited. The current feed maps The OpenNMS Group/Horizon (generic), The OpenNMS Group/Meridian (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 Sep 10, 2026Updated Sep 10, 2026Source checked Sep 10, 2026First seen by HOL Sep 10, 2026Material review Sep 10, 2026

Upstream Advisory

Key facts

Risk: Unknown severitySource severity not reported
Exploitation: Not marked as known exploited
Affected software: 2 mapped packages or products
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 The OpenNMS Group/Horizon (generic), The OpenNMS Group/Meridian (generic). Check affected ranges and fixed versions before updating.

Mapped affected packages and fixed versions
Package	Affected range	Fixed version
The OpenNMS Group/Horizongeneric	>=36.0.0 <36.0.4	36.0.4
The OpenNMS Group/Meridiangeneric	>=2024.1.0 <2024.3.13 \|\| >=2025.0.0 <2025.0.10	2024.3.13, 2025.0.10

Recommended response

Check inventory. Check lockfiles and deployed manifests for The OpenNMS Group/Horizon, The OpenNMS Group/Meridian.
Review the reported fix. Update The OpenNMS Group/Horizon to 36.0.4; The OpenNMS Group/Meridian to 2024.3.13 if you use the affected versions. Test the change in a non-production environment first.

Evidence timeline and material changes

Published upstream
Sep 10, 2026
Evidence: source:cvelist:source_dates:source-dates:record
Source modified
Sep 10, 2026
Evidence: source:cvelist:source_dates:source-dates:record
First seen by HOL
Sep 10, 2026

Sources and claim methodology

GitHub security advisorygithub.com

Upstream source description

An XML External Entity (XXE) vulnerability exists in the XML collector of multiple versions of OpenNMS Meridian and Horizon. When OpenNMS collects XML from a source whose response is attacker-controlled (for example a compromised monitored host or an HTTP man-in-the-middle position), the collector's XML parser resolves external entities and external DTDs. This allows an attacker to read files accessible to the OpenNMS service account, including database credentials, and to induce out-of-band requests. The solution is to upgrade to Meridian 2024.3.13, 2025.0.10 and Horizon 36.0.4 or newer. Meridian and Horizon installation instructions state that they are intended for installation within an organization's private networks and should not be directly accessible from the Internet.

Quoted source text, attributed separately from HOL analysis.