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://web.nvd.nist.gov/view/vuln/detail?vulnId=CVE-2015-2327
