There is a possible regular expression based DoS vulnerability in Action
Dispatch related to the If-None-Match header. This vulnerability has been
assigned the CVE identifier CVE-2023-22795.

Versions Affected: All
Not affected: None
Fixed Versions: 5.2.8.15 (Rails LTS), 6.1.7.1, 7.0.4.1

Impact

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.

Workarounds

We recommend that all users upgrade to one of the FIXED versions. In the
meantime, users can mitigate this vulnerability by using a load balancer or
other device to filter out malicious If-None-Match headers before they reach
the application.

Users on Ruby 3.2.0 or greater are not affected by this vulnerability.