The attemptAuthentication function in Component/Security/Http/Firewall/UsernamePasswordFormAuthenticationListener.php in Symfony before 2.3.41 2.7.x before 2.7.13 2.8.x before 2.8.6 and 3.0.x before 3.0.6 does not limit the length of a username stored in a session which allows remote attackers to cause a denial of service (session storage consumption) via a series of authentication attempts with long non-existent usernames.