In OpenNMS Horizon, versions opennms-1-0-stable 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-2020.1.6-1 are vulnerable to CSRF, due to no CSRF protection at `/opennms/admin/userGroupView/users/updateUser`. This flaw allows assigning `ROLE_ADMIN` security role to a normal user. Using this flaw, an attacker can trick the admin user to assign administrator privileges to a normal user by enticing him to click upon an attacker-controlled website.