PCRE before 8.36 mishandles the /((?(R)a|(?1)))+/ pattern and related patterns with certain recursion, 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.
https://jira.mongodb.org/browse/SERVER-17252
http://www.securityfocus.com/bid/74924
http://www.oracle.com/technetwork/topics/security/linuxbulletinapr2016-2952096.html
http://www.openwall.com/lists/oss-security/2015/11/29/1
http://www.fortiguard.com/advisory/FG-VD-15-014/
http://www-01.ibm.com/support/docview.wss?uid=isg3T1023886