ReDoS based DoS vulnerability in Active Support's underscore

There is a possible regular expression based DoS vulnerability in Active Support. This vulnerability has been assigned the CVE identifier CVE-2023-22796.

Versions Affected: All Not affected: None Fixed Versions: 5.2.8.15 (Rails LTS, which is a paid service and not part of the rubygem), 6.1.7.1, 7.0.4.1
Impact

A specially crafted string passed to the underscore method can cause the regular expression engine to enter a state of catastrophic backtracking. This can cause the process to use large amounts of CPU and memory, leading to a possible DoS vulnerability.

This affects String#underscore, ActiveSupport::Inflector.underscore, String#titleize, and any other methods using these.

All users running an affected release should either upgrade or use one of the workarounds immediately.
Releases

The FIXED releases are available at the normal locations.
Workarounds

There are no feasible workarounds for this issue.

Users on Ruby 3.2.0 or greater may be able to reduce the impact by configuring Regexp.timeout.
Patches

To aid users who aren’t able to upgrade immediately we have provided patches for the two supported release series. They are in git-am format and consist of a single changeset.

6-1-Avoid-regex-backtracking-in-Inflector.underscore.patch - Patch for 6.1 series
7-0-Avoid-regex-backtracking-in-Inflector.underscore.patch - Patch for 7.0 series

Please note that only the 7.0.Z and 6.1.Z series are supported at present, and 6.0.Z for severe vulnerabilities. Users of earlier unsupported releases are advised to upgrade as soon as possible as we cannot guarantee the continued availability of security fixes for unsupported releases.