The finish_nested_data function in ext/standard/var_unserializer.re in PHP before 5.6.31, 7.0.x before 7.0.21, and 7.1.x before 7.1.7 is prone to a buffer over-read while unserializing untrusted data. Exploitation of this issue can have an unspecified impact on the integrity of PHP.
https://www.debian.org/security/2018/dsa-4081
https://www.debian.org/security/2018/dsa-4080
https://usn.ubuntu.com/3566-2/
https://usn.ubuntu.com/3566-1/
https://bugs.php.net/bug.php?id=74111
https://access.redhat.com/errata/RHSA-2018:1296
http://www.securityfocus.com/bid/99490