session.c in the session extension in PHP before 5.2.13, and 5.3.1, does not properly interpret ; (semicolon) characters in the argument to the…

session.c in the session extension in PHP before 5.2.13, and 5.3.1, does not properly interpret ; (semicolon) characters in the argument to the session_save_path function, which allows context-dependent attackers to bypass open_basedir and safe_mode restrictions via an argument that contains multiple ; characters in conjunction with a .. (dot dot).