WordPress before 4.5 does not consider octal and hexadecimal IP address formats when determining an intranet address, which allows remote attackers to bypass an intended SSRF protection mechanism via a crafted address.
https://wpvulndb.com/vulnerabilities/8473
https://euvd.enisa.europa.eu/vulnerability/EUVD-2016-5035
https://core.trac.wordpress.org/query?status=closed&milestone=4.5
http://www.securitytracker.com/id/1036594