The regex code in Webkit 2.4.11 allows remote attackers to cause a denial of service (memory consumption) as demonstrated in a large number of ($ (open parenthesis and dollar) followed by {-2,16} and a large number of +) (plus close parenthesis).
https://security.gentoo.org/glsa/201706-15
http://www.securitytracker.com/id/1038137
http://www.securityfocus.com/bid/94559