CVE-2023-22795

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: 5.2.8.15 (Rails LTS), 6.1.7.1, 7.0.4.1

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.
Releases

The FIXED releases are available at the normal locations.
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.
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-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.

A regular expression with worst-case exponential or polynomial matching time is applied to untrusted input, causing excessive CPU use. Typical impact: denial of service when input is crafted to trigger backtracking.

Kodem intelligence

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1. What is CVE-2023-22795? CVE-2023-22795 is a low-severity inefficient regular expression (ReDoS) vulnerability in actionpack (rubygems), affecting versions >= 7.0.0, < 7.0.4.1. It is fixed in 7.0.4.1, 6.1.7.1. A regular expression with worst-case exponential or polynomial matching time is applied to untrusted input, causing excessive CPU use.
2. Which versions of actionpack are affected by CVE-2023-22795? actionpack (rubygems) versions >= 7.0.0, < 7.0.4.1 is affected.
3. Is there a fix for CVE-2023-22795? Yes. CVE-2023-22795 is fixed in 7.0.4.1, 6.1.7.1. Upgrade to this version or later.
4. Is CVE-2023-22795 exploitable, and should I be worried? Whether CVE-2023-22795 is exploitable in your environment depends on whether the vulnerable code is present and reachable. A CVSS score is a worst-case rating; it does not account for your specific deployment, configuration, or usage patterns. Kodem, an Intelligent Application Security platform, uses runtime intelligence to show which vulnerabilities actually execute in production, so you can focus on the ones that represent real risk. Get a demo
5. What actually determines whether CVE-2023-22795 is exploitable, and how bad it is? Exploitability and impact are not fixed properties of a CVE. They depend on runtime truth: whether the vulnerable code is present, reachable, and actually executes in your application. A high CVSS score on a dependency that never runs is not the same as real risk. Kodem, an Intelligent Application Security platform, uses runtime intelligence to reveal which vulnerabilities actually execute in production, so teams prioritize the ones that genuinely matter.
6. How do I fix CVE-2023-22795?
   • Upgrade actionpack to 7.0.4.1 or later
   • Upgrade actionpack to 6.1.7.1 or later

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