PCRE before 8.38 mishandles the /(?:|a|){100}x/ pattern and related patterns, which allows remote attackers to cause a denial of service (infinite recursion) or possibly have unspecified other impact via a crafted regular expression, as demonstrated by a JavaScript RegExp object encountered by Konqueror.
http://web.nvd.nist.gov/view/vuln/detail?vulnId=CVE-2015-8389
