CVE-2026-19596: OpenNMS XML External Entity injection in XML collector

CVE-2026-19596 · Severity: medium · CVSS 5.9 · Published 2026-09-10

OpenNMS Meridian and Horizon are network monitoring platforms that collect and process data from monitored systems. An XML External Entity (XXE) vulnerability in their XML collector allows an attacker who controls the source of monitored XML data—such as a compromised monitored host or via network interception—to read sensitive files (including database credentials) accessible to the OpenNMS service account and trigger out-of-band network requests. This could lead to exposure of credentials and further compromise of the monitoring infrastructure.

Technologies: OpenNMS Meridian. Vendors: OpenNMS.

Quick answers

Is CVE-2026-19596 exploited in the wild?
No. Junglewise Threat Intelligence has no report of CVE-2026-19596 being exploited in the wild.
How severe is CVE-2026-19596?
Medium severity, with a CVSS score of 5.9, published 10 September 2026.
Which products and versions are affected?
OpenNMS Meridian versions prior to 2024.3.13, 2025.0.10.
Is there a fix for CVE-2026-19596?
A patch was published on 2026-08-21: Fix merged in PR #8782 (foundation-2023 branch) Junglewise finds every place you run it, drafts the upgrade and applies it once you approve.
How is CVE-2026-19596 attacked?
It is attacked over the network or from the adjacent network, in a hosted service.
Am I affected by CVE-2026-19596?
Check whether you run OpenNMS Meridian at an affected version. Junglewise does that check for you around the clock: connect your code, cloud and domains, and it matches new vulnerabilities like this one against what you actually run and tells you when one reaches you.

Technical details

An XML External Entity (XXE) vulnerability exists in the XML collector component of OpenNMS Meridian and Horizon due to improper configuration of XML parsers (DocumentBuilderFactory and TransformerFactory in AbstractXmlCollectionHandler). The parser resolves external entities and external DTDs without restriction. An attacker with control over XML responses returned during collection—achievable via a compromised monitored host, man-in-the-middle network position, or similar attack vector—can craft malicious XML to read arbitrary files accessible to the OpenNMS service account (such as database credentials) or induce out-of-band HTTP/DNS requests. The fix disables external entity and DTD resolution in the affected XML factories. Patches are available in Meridian 2024.3.13, 2025.0.10, and Horizon 36.0.4.

Affected products

  • OpenNMS Meridian versions prior to 2024.3.13, 2025.0.10
  • OpenNMS Horizon versions prior to 36.0.4

Timeline

  • 2026-09-10: disclosed: CVE-2026-19596 published
  • 2026-08-21: patched: Fix merged in PR #8782 (foundation-2023 branch)

References

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