Advantech WISE-DeviceOn Server versions prior to 5.4 contain a stored cross-site scripting (XSS) vulnerability in the /rmm/v1/rule-engines endpoint. When an authenticated user creates or updates a rule for an agent, the rule fields min, max, and unit are stored and later rendered in rule listings or detail views without proper HTML sanitation. An attacker can inject malicious script into one or more of these fields, which is then executed in the browser context of users who view or interact with the affected rule, potentially enabling session compromise and unauthorized actions as the victim.