CVE-2026-111252 is a denial of service vulnerability in OpenNMS Meridian and Horizon XML parsing. It occurs due to improper restriction of recursive entity references in DTDs, allowing an authenticated user with provisioning access to supply XML documents that cause excessive entity expansion and exhaust server memory. The vulnerability affects multiple versions prior to Meridian 2024.3.14, 2025.0.11, 2026.0.1 and Horizon 36.0.5. The vendor has released fixes that cap entity expansions and reject DOCTYPE declarations in requisition and foreign-source XML. These products are intended for private network installation and not direct Internet exposure.
CVE-2026-111235 is a critical authorization bypass vulnerability in the REST API of multiple versions of OpenNMS Meridian and Horizon. The issue arises from case-sensitive HTTP method checks in Spring Security filter chains, allowing requests with non-canonical (e.g., lowercase) HTTP methods to bypass authentication. This enables remote unauthenticated attackers to read monitored inventory and create, modify, or delete resources, including injecting events to manipulate alarms. The vulnerability is fixed by adding terminal deny rules to REST filter chains. Upgrading to Meridian 2024.3.14, 2025.0.11, 2026.0.1 or Horizon 36.0.5 or newer resolves the issue. These products are intended for private network use and should not be exposed directly to the Internet.
A SQL injection vulnerability (CWE-89) exists in the JasperReports-based reporting feature of OpenNMS Meridian and Horizon. A low-privileged authenticated user can exploit this by supplying a crafted DATE_FORMAT parameter to certain default-enabled reports via the reporting REST API, leading to arbitrary SQL execution and unauthorized data access. The vulnerability affects specific versions of Meridian and Horizon prior to fixed releases. Upgrading to Meridian 2024.3.13, 2025.0.10 or Horizon 36.0.4 or newer mitigates the issue. These products are intended for private network deployment and not direct Internet exposure.
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.
A missing authorization vulnerability in OpenNMS Horizon allows configuration changes without authentication. The Spring Security policy for the /api/v2 REST API defines authorization rules for every HTTP method except PATCH, so the shipped @PATCH configuration endpoints for event configuration and SNMP data collection (which enable and disable event definitions and data-collection sources) are reachable with no authorization enforced. An unauthenticated attacker able to reach the web UI can disable event definitions and SNMP data collection, suppressing event and alarm generation and stopping metric collection - silently degrading monitoring and detection - with the change persisted and reloaded into the running system.
The solution is to upgrade to 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.
An incorrect authorization check in the v2 Alarm REST API in OpenNMS Meridian and Horizon allows a low-privileged authenticated user (ROLE_REST) to acknowledge, escalate, or clear alarms recorded as an arbitrary username, and, when also assigned ROLE_READONLY, to modify alarm state despite the read-only restriction. A credential check that should restrict these operations is guarded by an inverted condition, so it never executes for a real (non-blank) username. This can potentially allow an attacker to compromise the integrity of alarm state and audit records.
The solution is to upgrade to Meridian 2024.3.12, 2025.0.9 and Horizon 36.0.3 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.
A JEXL expression sandbox bypass exists in multiple versions of OpenNMS Meridian and Horizon. A low-privileged authenticated user can submit a crafted expression to the Measurements REST API that escapes the sandbox and loads arbitrary Java classes on the server. This can potentially allow an attacker to gain access to confidential information and compromise integrity.
The solution is to upgrade to Meridian 2024.3.12, 2025.0.9 and Horizon 36.0.3 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.
Improper Neutralization of Special Elements used in an SQL Command ('SQL Injection') vulnerability in OpenNMS Horizon and Meridian applications allows SQL Injection.
Users
should upgrade to Meridian 2024.2.6 or newer, or Horizon 33.16 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.
Multiple stored XSS were found on different nodes with unsanitized parameters in OpenMNS Horizon 33.0.8 and versions earlier than 33.1.6 on multiple platforms that allow an attacker to store on database and then inject HTML and/or Javascript on the page. The solution is to upgrade to Horizon 33.1.6, 33.1.7 or Meridian 2024.2.6, 2024.2.7 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. OpenNMS thanks Fábio Tomé for reporting this issue.