HIGH
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.
http://php.net/ChangeLog-5.php
http://php.net/ChangeLog-7.php
http://www.securityfocus.com/bid/99490
https://access.redhat.com/errata/RHSA-2018:1296
https://bugs.php.net/bug.php?id=74111
https://usn.ubuntu.com/3566-1/
Source: MITRE
Published: 2017-08-18
Updated: 2018-05-04
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