Action Mailer is a framework for designing email service layers. Starting in version 3.0.0 and prior to versions 6.1.7.9, 7.0.8.5, 7.1.4.1, and 7.2.1.1, there is a possible ReDoS vulnerability in the block_format helper in Action Mailer. Carefully crafted text can cause the block_format helper to take an unexpected amount of time, possibly resulting in a DoS vulnerability. All users running an affected release should either upgrade to versions 6.1.7.9, 7.0.8.5, 7.1.4.1, or 7.2.1.1 or apply the relevant patch immediately. As a workaround, users can avoid calling the block_format helper or upgrade to Ruby 3.2. Ruby 3.2 has mitigations for this problem, so Rails applications using Ruby 3.2 or newer are unaffected. Rails 8.0.0.beta1 requires Ruby 3.2 or greater so is unaffected.