In OpenNMS Horizon, versions opennms-17.0.0-1 through opennms-27.1.0-1; OpenNMS Meridian, versions meridian-foundation-2015.1.0-1 through meridian-foundation-2019.1.18-1; meridian-foundation-2020.1.0-1 through meridian-foundation-2020.1.7-1 are vulnerable to Stored Cross-Site Scripting, since the function `add()` performs improper validation checks on the input sent to the `foreign-source` parameter. Due to this flaw an attacker could bypass the existing regex validation and inject an arbitrary script which will be stored in the database.