PCRE before 8.38 mishandles the /(?|(\k'Pm')|(?'Pm'))/ pattern and related patterns with certain forward references, which allows remote attackers to cause a denial of service (buffer overflow) 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-2016-1025.html
http://rhn.redhat.com/errata/RHSA-2016-2750.html
https://access.redhat.com/errata/RHSA-2016:1132
https://security.gentoo.org/glsa/201607-02
http://www-01.ibm.com/support/docview.wss?uid=isg3T1023886
http://www.openwall.com/lists/oss-security/2015/11/29/1
http://www.oracle.com/technetwork/topics/security/linuxbulletinapr2016-2952096.html