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://openwall.com/lists/oss-security/2016/09/02/9
http://rhn.redhat.com/errata/RHSA-2016-2750.html
http://www.php.net/ChangeLog-5.php
http://www.php.net/ChangeLog-7.php
http://www.securityfocus.com/bid/92552
http://www.securitytracker.com/id/1036680
https://bugs.php.net/bug.php?id=72681
https://github.com/php/php-src/commit/8763c6090d627d8bb0ee1d030c30e58f406be9ce?w=1
Source: MITRE
Published: 2016-09-12
Updated: 2018-01-05
Type: CWE-74
Base Score: 5
Vector: AV:N/AC:L/Au:N/C:N/I:P/A:N
Impact Score: 2.9
Exploitability Score: 10
Severity: MEDIUM
Base Score: 7.5
Vector: CVSS:3.0/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:H/A:N
Impact Score: 3.6
Exploitability Score: 3.9
Severity: HIGH