A regular expression based DoS vulnerability in Action Dispatch <6.1.7.1and<7.0.4.1relatedtotheIf-None-Matchheader.AspeciallycraftedHTTPIf-None-Matchheadercancausetheregularexpressionenginetoenterastateofcatastrophicbacktracking,whenonaversionofRubybelow3.2.0.ThiscancausetheprocesstouselargeamountsofCPUandmemory,leadingtoapossibleDoSvulnerabilityAllusersrunninganaffectedreleaseshouldeitherupgradeoruseoneoftheworkaroundsimmediately.