ext/session/session.c in PHP before 5.6.25 and 7.x before 7.0.10 skips invalid session names in a way that triggers incorrect parsing, which allows remote attackers to inject arbitrary-type session data by leveraging control of a session name, as demonstrated by object injection. http://web.nvd.nist.gov/view/vuln/detail?vulnId=CVE-2016-7125
