CVE-2026-111252
MediumCVSS 6.5Exploitation Probability (EPSS)
Low risk15th percentile - higher than 15% of all known CVEs
Summary
OpenNMS Meridian and Horizon XML parsing lacked an effective limit on entity expansion, allowing server memory exhaustion. An authenticated user with provisioning access can supply a document with a DOCTYPE and internal entities via requisition or foreign-source import, causing a denial of service.
Risk Assessment
An attacker with provisioning privileges can exhaust server memory and cause OpenNMS unavailability, disrupting infrastructure monitoring. The risk applies to internal installations but can be exploited by a malicious internal user.
Recommendation
Upgrade OpenNMS Meridian to 2024.3.14, 2025.0.11, 2026.0.1 or newer, and Horizon to 36.0.5 or newer. Ensure the system is not directly accessible from the Internet.
Other vulnerabilities in OpenNMS
See all- CVE-2015-7856High
OpenNMS has a default password of 'rtc' for the rtc account, which makes it easier for remote attackers to obtain access by leveraging knowledge of the credentials.
- CVE-2026-19182Medium
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 is guarded by an inverted condition, so it never executes for a real (non-blank) username.
- CVE-2026-19135Medium
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.
Original NVD description (English source)
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.
Vulnerability data from NVD (NIST) · CISA KEV · EPSS