[CVE-2023-22795] Possible ReDoS based DoS vulnerability in Action Dispatch

Possible ReDoS based DoS vulnerability in Action Dispatch

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:,


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.


The FIXED releases are available at the normal locations.


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.


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-on-If-None-Match-header.patch - Patch for 6.1 series
  • 7-0-Avoid-regex-backtracking-on-If-None-Match-header.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.


We would like to thank wonda_tea_coffee for reporting this

6-1-Avoid-regex-backtracking-on-If-None-Match-header.patch (869 Bytes)

7-0-Avoid-regex-backtracking-on-If-None-Match-header.patch (869 Bytes)