OpenNMS Group Horizon/Meridian XML collector xml external entity reference

Summaryinfo

A vulnerability labeled as critical has been found in OpenNMS Group Horizon and Meridian. Affected by this issue is some unknown functionality of the component XML collector. The manipulation results in xml external entity reference. This vulnerability is identified as CVE-2026-19596. The attack can be executed remotely. There is not any exploit available.

Detailsinfo

A vulnerability was found in OpenNMS Group Horizon and Meridian (the affected version unknown). It has been classified as critical. Affected is an unknown part of the component XML collector. The manipulation with an unknown input leads to a xml external entity reference vulnerability. CWE is classifying the issue as CWE-611. The product processes an XML document that can contain XML entities with URIs that resolve to documents outside of the intended sphere of control, causing the product to embed incorrect documents into its output. This is going to have an impact on confidentiality, integrity, and availability. CVE summarizes:

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.

The advisory is shared for download at github.com. This vulnerability is traded as CVE-2026-19596 since 08/12/2026. The exploitability is told to be easy. It is possible to launch the attack remotely. The exploitation doesn't require any form of authentication. There are neither technical details nor an exploit publicly available. The current price for an exploit might be approx. USD $0-$5k (estimation calculated on 09/10/2026).

There is no information about possible countermeasures known. It may be suggested to replace the affected object with an alternative product.

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Productinfo

Vendor

• OpenNMS Group

Name

• Horizon
• Meridian

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