Session fixation vulnerability in the Sessions subsystem in PHP before 5.5.2 allows remote attackers to hijack web sessions by specifying a session ID.
https://wiki.php.net/rfc/strict_sessions
https://bugs.php.net/bug.php?id=60491
http://git.php.net/?p=php-src.git%3Ba=commit%3Bh=25e8fcc88fa20dc9d4c47184471003f436927cde
http://git.php.net/?p=php-src.git%3Ba=commit%3Bh=169b78eb79b0e080b67f9798708eb3771c6d0b2f