PostgreSQL versions before 9.4.13, 9.5.8 and 9.6.4 are vulnerable to authorization flaw allowing remote authenticated attackers with no privileges on a large object to overwrite the entire contents of the object, resulting in a denial of service.
https://www.postgresql.org/about/news/1772/
https://security.gentoo.org/glsa/201710-06
https://access.redhat.com/errata/RHSA-2017:2678
https://access.redhat.com/errata/RHSA-2017:2677
http://www.securitytracker.com/id/1039142
http://www.securityfocus.com/bid/100276