@dapperduckling/keycloak-connector-server is an opinionated series of libraries for Node.js applications and frontend clients to interface with keycloak. A Reflected Cross-Site Scripting (XSS) vulnerability was discovered in the authentication flow of the application. This issue arises due to improper sanitization of the URL parameters, allowing the URL bar's contents to be injected and reflected into the HTML page. An attacker could craft a malicious URL to execute arbitrary JavaScript in the browser of a victim who visits the link. Any application utilizing this authentication library is vulnerable. Users of the application are at risk if they can be lured into clicking on a crafted malicious link. The vulnerability has been patched in version 2.5.5 by ensuring proper sanitization and escaping of user input in the affected URL parameters. Users are strongly encouraged to upgrade. If upgrading is not immediately possible, users can implement the following workarounds: 1. Employ a Web Application Firewall (WAF) to block malicious requests containing suspicious URL parameters. or 2. Apply input validation and escaping directly within the application’s middleware or reverse proxy layer, specifically targeting the affected parameters.