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.
Exploitability
AV:NAC:LAu:NImpact
C:PI:PA:P7.5/AV:N/AC:L/Au:N/C:P/I:P/A:P