The SplObjectStorage unserialize implementation in ext/spl/spl_observer.c in PHP before 7.0.12 does not verify that a key is an object, which allows remote attackers to execute arbitrary code or cause a denial of service (uninitialized memory access) via crafted serialized data.
http://blog.checkpoint.com/wp-content/uploads/2016/12/PHP_Technical_Report.pdf
http://php.net/ChangeLog-7.php
http://www.securityfocus.com/bid/95152
https://bugs.php.net/bug.php?id=73257
https://github.com/php/php-src/commit/61cdd1255d5b9c8453be71aacbbf682796ac77d4
Source: MITRE
Published: 2017-01-11
Updated: 2018-01-14
Type: CWE-119
Base Score: 7.5
Vector: AV:N/AC:L/Au:N/C:P/I:P/A:P
Impact Score: 6.4
Exploitability Score: 10
Severity: HIGH
Base Score: 9.8
Vector: CVSS:3.0/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:H/A:H
Impact Score: 5.9
Exploitability Score: 3.9
Severity: CRITICAL