OpenNMS Group Meridian/Horizon prior 2024.3.14/2025.0.11/2026.0.1/36.0.5 XML Parsing resource consumption

Summaryinfo

A vulnerability identified as problematic has been detected in OpenNMS Group Meridian and Horizon. The affected element is an unknown function of the component XML Parsing. This manipulation causes resource consumption. This vulnerability is tracked as CVE-2026-111252. The attack is possible to be carried out remotely. No exploit exists. You should upgrade the affected component.

Detailsinfo

A vulnerability classified as problematic was found in OpenNMS Group Meridian and Horizon. Affected by this vulnerability is some unknown functionality of the component XML Parsing. The manipulation with an unknown input leads to a resource consumption vulnerability. The CWE definition for the vulnerability is CWE-400. The product does not properly control the allocation and maintenance of a limited resource, thereby enabling an actor to influence the amount of resources consumed, eventually leading to the exhaustion of available resources. As an impact it is known to affect availability. The summary by CVE is:

A denial of service vulnerability exists in the XML parsing of multiple versions of OpenNMS Meridian and Horizon. OpenNMS parsed XML without an effective limit on entity expansion. A document with a DOCTYPE that declares internal entities can expand to a very large value and exhaust the server memory. An authenticated user with provisioning access can supply such a document through a requisition or foreign-source import, which includes a remote requisition URL that the server fetches and parses. Both deeply nested entities and a single large entity referenced many times cause the memory exhaustion. The fix caps the number of entity expansions for all XML parsing and rejects any DOCTYPE in requisition and foreign-source XML. The solution is to upgrade to Meridian 2024.3.14, 2025.0.11, 2026.0.1 and Horizon 36.0.5 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 at github.com. This vulnerability is known as CVE-2026-111252 since 10/15/2026. The exploitation appears to be easy. The attack can be launched remotely. Neither technical details nor an exploit are publicly available. MITRE ATT&CK project uses the attack technique T1499 for this issue.

Upgrading to version 2024.3.14, 2025.0.11, 2026.0.1 or 36.0.5 eliminates this vulnerability.

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Productinfo

Vendor

• OpenNMS Group

Name

• Horizon
• Meridian

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