CVE-2026-19596 OpenNMS XML collector XXE allows arbitrary file read from the OpenNMS host
An XXE vulnerability in OpenNMS allows attackers to read sensitive files and induce out-of-band requests via malicious XML responses.
- Exploited in the wild
- Not known
- Login needed
- Not needed
- Attackable
- Over the internet
- Victim action needed
- Not needed
- Fix
- None listed
What is CVE-2026-19596?
CVE-2026-19596 is a medium-severity vulnerability in The OpenNMS Group Horizon, published on 10 Sep 2026. An attacker can exploit it over the internet without logging in, with no action from the victim.
Official description
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.
Weakness: CWE-611
Which versions are affected by CVE-2026-19596?
How do I fix CVE-2026-19596?
No fix has been published for CVE-2026-19596 yet. Limit exposure of the affected software until one is available.
Is CVE-2026-19596 being exploited?
There is no known exploitation of CVE-2026-19596 in the wild and no public exploit code.
Sources
Also known as GHSA-9hqx-g6f2-rj2p.