An issue was discovered in the Security component in Symfony 2.7.x before 2.7.48, 2.8.x before 2.8.41, 3.3.x before 3.3.17, 3.4.x before 3.4.11, and 4.0.x before 4.0.11. A session fixation vulnerability within the "Guard" login feature may allow an attacker to impersonate a victim towards the web application if the session id value was previously known to the attacker.