Cross-site scripting in outage/list.htm in multiple versions of OpenNMS Meridian and Horizon allows an attacker access to confidential session information. The solution is to upgrade to Meridian 2023.1.0 or newer, or Horizon 31.0.4 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.