CVE-2026-111252 OpenNMS denial of service via XML entity expansion
An authenticated user can cause denial of service in OpenNMS by submitting XML with excessive entity expansion, exhausting server memory.
- Exploited in the wild
- Not known
- Login needed
- Any signed-in user
- Attackable
- Over the internet
- Victim action needed
- Not needed
- Fix
- None listed
What is CVE-2026-111252?
CVE-2026-111252 is a medium-severity vulnerability in The OpenNMS Group Horizon, published on 15 Oct 2026. Any signed-in user can exploit it over the network, with no action from the victim.
Official description
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.
Which versions are affected by CVE-2026-111252?
How do I fix CVE-2026-111252?
No fix has been published for CVE-2026-111252 yet. Limit exposure of the affected software until one is available.
Is CVE-2026-111252 being exploited?
There is no known exploitation of CVE-2026-111252 in the wild and no public exploit code.
Sources
Also known as GHSA-vc8g-329j-xw8w.