CVE-2026-111252
Received Received - Intake

XML Entity Expansion DoS in OpenNMS Meridian and Horizon

Publication date: 2026-10-15

Last updated on: 2026-10-15

Assigner: The OpenNMS Group

Description
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.

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Meta Information

Published
2026-10-15
Last Modified
2026-10-15
Generated
2026-10-16
AI Q&A
2026-10-15
EPSS Evaluated
N/A
NVD
CVE-2026-111252
EUVD
EUVD-2026-102348

Affected Vendors & Products

Showing 4 associated CPEs
Vendor Product Version / Range
The OpenNMS Group Meridian 2024.1.0
The OpenNMS Group Meridian 2025.0.0
The OpenNMS Group Meridian 2026.0.0
The OpenNMS Group Horizon 36.0.0

Helpful Resources

Exploitability

CWE
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KEV
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CWE ID Description
CWE-776 The product uses XML documents and allows their structure to be defined with a Document Type Definition (DTD), but it does not properly control the number of recursive definitions of entities.
CWE-400 The product does not properly control the allocation and maintenance of a limited resource.

Attack-Flow Graph

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Executive Summary

This vulnerability is a denial of service issue in OpenNMS Meridian and Horizon. It occurs when XML parsing lacks limits on entity expansion, allowing a document with a DOCTYPE declaring internal entities to consume excessive server memory. An authenticated user with provisioning access can exploit this by supplying a malicious document via requisition or foreign-source import, including a remote URL that the server fetches and parses. Both deeply nested entities and large entities referenced repeatedly cause memory exhaustion.

Detection Guidance

Detecting this vulnerability requires checking for excessive memory usage during XML parsing in OpenNMS. Monitor system logs for memory exhaustion errors during XML processing. Check for large or malformed XML files in requisition or foreign-source import directories. Use tools like 'top' or 'htop' to observe memory spikes when processing XML files.

Impact Analysis

This vulnerability can cause your OpenNMS server to crash or become unresponsive due to memory exhaustion. If exploited, it may disrupt services, leading to downtime for network monitoring and management. Only users with provisioning access can trigger this issue, but the impact affects the entire system.

Mitigation Strategies

Upgrade OpenNMS to Meridian 2024.3.14, 2025.0.11, 2026.0.1 or Horizon 36.0.5 or newer. Ensure OpenNMS instances are not directly accessible from the Internet. Restrict provisioning access to trusted users only. Monitor memory usage and block XML files with DOCTYPE declarations if detected.

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