Vulnerability · Published Oct 15, 2026 · Assigned by OpenNMS
CVE-2026-111252OpenNMS denial of service via XML entity expansion
Medium 6.5
In plain English
A medium-severity uncontrolled resource consumption in Horizon from The OpenNMS Group. There are no confirmed reports of exploitation so far. The chance it is exploited in the next 30 days is estimated at 0.2% (higher than 16% of all known vulnerabilities).
Official 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.
Affected products (as reported)
| Vendor | Product | Versions |
|---|---|---|
| The OpenNMS Group | Meridian | 2024.1.0 – before 2024.3.142025.0.0 – before 2025.0.112026.0.0 – before 2026.0.1 |
| The OpenNMS Group | Horizon | 36.0.0 – before 36.0.5 |
Weakness: CWE-776, CWE-400 · Vector: CVSS:3.1/AV:N/AC:L/PR:L/UI:N/S:U/C:N/I:N/A:H