Unauthenticated, stored cross-site scripting in the display of alarm reduction keys in multiple versions of OpenNMS Horizon and Meridian could allow an attacker access to confidential session information. Users should upgrade to Meridian 2023.1.0 or newer, or Horizon 31.0.4. 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.