The nextBytes function in the SecureRandom class in Symfony before 2.3.37, 2.6.x before 2.6.13, and 2.7.x before 2.7.9 does not properly generate random numbers when used with PHP 5.x without the paragonie/random_compat library and the openssl_random_pseudo_bytes function fails, which makes it easier for attackers to defeat cryptographic protection mechanisms via unspecified vectors.

Symfony 2.3.x before 2.3.35, 2.6.x before 2.6.12, and 2.7.x before 2.7.7 might allow remote attackers to have unspecified impact via a timing attack involving the (1) Symfony/Component/Security/Http/RememberMe/PersistentTokenBasedRememberMeServices or (2) Symfony/Component/Security/Http/Firewall/DigestAuthenticationListener class in the Symfony Security Component, or (3) legacy CSRF implementation from the Symfony/Component/Form/Extension/Csrf/CsrfProvider/DefaultCsrfProvider class in the Symfony Form component.

Session fixation vulnerability in the "Remember Me" login feature in Symfony 2.3.x before 2.3.35, 2.6.x before 2.6.12, and 2.7.x before 2.7.7 allows remote attackers to hijack web sessions via a session id.

FragmentListener in the HttpKernel component in Symfony 2.3.19 through 2.3.28, 2.4.9 through 2.4.10, 2.5.4 through 2.5.11, and 2.6.0 through 2.6.7, when ESI or SSI support enabled, does not check if the _controller attribute is set, which allows remote attackers to bypass URL signing and security rules by including (1) no hash or (2) an invalid hash in a request to /_fragment.