A regular expression based DoS vulnerability in Action Dispatch <6.1.7.1 and <7.0.4.1 related to the If-None-Match header. A specially crafted HTTP If-None-Match header can cause the regular expression engine to enter a state of catastrophic backtracking when on a version of Ruby below 3.2.0. This can cause the process to use large amounts of CPU and memory leading to a possible DoS vulnerability All users running an affected release should either upgrade or use one of the workarounds immediately.

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