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Fencer Intel
medium 6.1

CVE-2026-127235 json

OpenNMS reflected cross-site scripting in the web UI via request parameters

published 2d ago modified 2d ago also EUVD-2026-124614

cvss
6.1
version 3.1, CNA
cisa kev
Not listed
not in CISA's catalog
epss
0.2%
EPSS 0.2% chance of exploitation in 30 days, percentile 7%
public exploits
0
none known

Summary

A reflected cross-site scripting vulnerability exists in the web user interface of multiple versions of OpenNMS Meridian and Horizon. Several web UI pages copy request parameter values into the HTML response without correct contextual output encoding. A remote attacker can craft a link that runs arbitrary JavaScript in the OpenNMS origin when an authenticated user opens it. The script runs in the victim's browser with the victim's session, so the attacker can read page data and send same-origin requests as the victim. The fix encodes the affected request values. On pages that use AngularJS, the fix also stops client-side template evaluation of the reflected values.

The solution is to upgrade to Meridian 2024.3.15, 2025.0.12, 2026.0.2 and Horizon 36.0.6 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.

Patch / fix

  • The OpenNMS Group Meridian 2024.3.15, 2025.0.12, 2026.0.2
  • The OpenNMS Group Horizon 36.0.6

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Exploit prediction

0.18% chance of exploitation in the next 30 days, higher than 7% of all scored CVEs (FIRST EPSS, 2026-11-14).

CVSS scores

assigned by version score vector
CNA 3.1 6.1 CVSS:3.1/AV:N/AC:L/PR:N/UI:R/S:C/C:L/I:L/A:N

Affected products

  • The OpenNMS Group Meridian
  • The OpenNMS Group Horizon

Classification

Weakness
  • CWE-79 Improper Neutralization of Input During Web Page Generation

References

Sources

Fencer Intel keeps one entry per vulnerability: the CVE id wins, then GHSA, and records that alias each other are merged, except that two CVEs always keep separate entries. The same data is available as JSON.