PCRE before 8.36 mishandles the /(((a\2)|(a*)\g<-1>))*/ pattern and related patterns with certain internal recursive back references, which allows remote attackers to cause a denial of service (segmentation fault) or possibly have unspecified other impact via a crafted regular expression, as demonstrated by a JavaScript RegExp object encountered by Konqueror.
http://rhn.redhat.com/errata/RHSA-2016-2750.html
http://vcs.pcre.org/pcre/code/trunk/ChangeLog?view=markup
http://www.fortiguard.com/advisory/FG-VD-15-010/
http://www.openwall.com/lists/oss-security/2015/11/29/1
http://www.securityfocus.com/bid/74924