In Symfony before 2.7.51, 2.8.x before 2.8.50, 3.x before 3.4.26, 4.x before 4.1.12, and 4.2.x before 4.2.7, a vulnerability would allow an attacker to authenticate as a privileged user on sites with user registration and remember me login functionality enabled. This is related to symfony/security.
https://www.synology.com/security/advisory/Synology_SA_19_19
https://symfony.com/blog/cve-2019-10911-add-a-separator-in-the-remember-me-cookie-hash
https://github.com/symfony/symfony/commit/a29ce2817cf43bb1850cf6af114004ac26c7a081