The DynamicPageList3 extension is a reporting tool for MediaWiki, listing category members and intersections with various formats and details. In affected versions unsanitised input of regular expression date within the parameters of the DPL parser function, allowed for the possibility of ReDoS (Regex Denial of Service). This has been resolved in version 3.3.6. If you are unable to update you may also set "$wgDplSettings['functionalRichness'] = 0;" or disable DynamicPageList3 to mitigate.