CVE-2026-19596: OpenNMS XML collector XXE allows arbitrary file read from the OpenNMS host
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.
Affected Software
Remediation
Recommended actions to resolve this vulnerability, in priority order.
- Upgrade
Upgrade
OpenNMS Meridianto a version that resolves this vulnerability.Fixed in 2024.3.13 - Upgrade
Upgrade
OpenNMS Meridianto a version that resolves this vulnerability.Fixed in 2025.0.10 - Upgrade
Upgrade
OpenNMS Horizonto a version that resolves this vulnerability.Fixed in 36.0.4 - Compensating control
Ensure OpenNMS Meridian/Horizon are installed within the organization's private network and are not directly accessible from the Internet to reduce attacker-controlled XML sources (e.g., compromised monitored hosts or HTTP man-in-the-middle).
Event History
Frequently Asked Questions
What conditions are required for exploitation?
An attacker must control the XML response from a monitored source, such as by compromising a monitored host, or be in an HTTP man-in-the-middle position. No OpenNMS authentication or user interaction is required according to the supplied vector.
What data or systems are at risk if exploitation succeeds?
The attacker can read files accessible to the OpenNMS service account, which may include database credentials. They can also cause out-of-band requests from the OpenNMS host.
Which deployments are most exposed?
Deployments that collect XML from monitored sources whose responses an attacker can control are exposed. The product installation guidance says Meridian and Horizon are intended for private networks and should not be directly accessible from the Internet.
Which versions contain the fix?
Upgrade to Meridian 2024.3.13 or 2025.0.10, or to Horizon 36.0.4 or newer.