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.
www.debian.org/security/2016/dsa-3588
github.com/FriendsOfPHP/security-advisories/blob/master/symfony/security-http/CVE-2016-4423.yaml
github.com/FriendsOfPHP/security-advisories/blob/master/symfony/security/CVE-2016-4423.yaml
github.com/FriendsOfPHP/security-advisories/blob/master/symfony/symfony/CVE-2016-4423.yaml
github.com/symfony/symfony
github.com/symfony/symfony/pull/18733
nvd.nist.gov/vuln/detail/CVE-2016-4423
symfony.com/blog/cve-2016-4423-large-username-storage-in-session
symfony.com/cve-2016-4423