CVE-2026-111235
CriticalCVSS 9.1Summary
An authorization bypass vulnerability exists in the REST API of multiple versions of OpenNMS Meridian and Horizon. The /rest/** Spring Security filter chains authorize requests with intercept-url rules that name the HTTP method as an uppercase token, compare the method case-sensitively, and have no terminal deny rule. A request that uses a non-canonical (for example lowercase) method token matches no rule and is processed without authentication. A remote, unauthenticated attacker can read the monitored inventory and can create, modify, or delete resources through the REST API, which includes injecting events to fabricate or suppress alarms. The /rest/alarms chain has the same missing deny rule and discloses whether an alarm exists through a difference in the response. The fix adds a terminal deny rule to each REST filter chain. 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.
Risk Assessment
An unauthenticated attacker can read and modify monitoring data and manipulate alarms, potentially leading to a false picture of infrastructure state and actions on resources.
Recommendation
Upgrade OpenNMS Meridian to 2024.3.14, 2025.0.11, 2026.0.1 or Horizon 36.0.5 (or newer) and ensure instances are not directly accessible from the Internet.
Other vulnerabilities in OpenNMS Meridian and Horizon
See all- CVE-2026-89089Medium
A SQL injection vulnerability exists in the JasperReports-based reporting feature of multiple versions of OpenNMS Meridian and Horizon. A low-privileged authenticated user (ROLE_USER) can run the shipped, default-enabled online reports "Maintenance contracts expired" and "Maintenance contracts strategy" via the reporting REST API (POST /rest/reports/{id}) and supply a DATE_FORMAT parameter that the report templates substitute literally, un-escaped, into their SQL queries, allowing arbitrary SQL execution and reading of arbitrary data including database-stored secrets.
- CVE-2026-19596Medium
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.
Original NVD description (English source)
An authorization bypass vulnerability exists in the REST API of multiple versions of OpenNMS Meridian and Horizon. The /rest/** Spring Security filter chains authorize requests with intercept-url rules that name the HTTP method as an uppercase token, compare the method case-sensitively, and have no terminal deny rule. A request that uses a non-canonical (for example lowercase) method token matches no rule and is processed without authentication. A remote, unauthenticated attacker can read the monitored inventory and can create, modify, or delete resources through the REST API, which includes injecting events to fabricate or suppress alarms. The /rest/alarms chain has the same missing deny rule and discloses whether an alarm exists through a difference in the response. The fix adds a terminal deny rule to each REST filter chain. 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.
Vulnerability data from NVD (NIST) · CISA KEV · EPSS