The Vigilant – 100% Free Security Suite: Firewall, 2FA, Login, Headers, Scanner… plugin for WordPress is vulnerable to Stored Cross-Site Scripting via User-Agent Header in all versions up to, and including, 2.10.2 due to insufficient input sanitization and output escaping. This makes it possible for unauthenticated attackers to inject arbitrary web scripts in pages that will execute whenever a user accesses an injected page. The malicious payload is delivered passively by any unauthenticated visitor who triggers a failed login attempt with a crafted User-Agent header, requiring no further interaction from the attacker once stored.