How severe is CVE-2021-22902?

CVE-2021-22902 has a CVSS score of 7.5/10, rated HIGH. Immediate patching is strongly recommended.

Which packages are affected by CVE-2021-22902?

CVE-2021-22902 affects the following packages: actionpack (RubyGems), actionpack (RubyGems). Ecosystems affected: RubyGems.

How do I fix CVE-2021-22902?

Update actionpack to 6.0.3.7 or later, then make sure no transitive (indirect) dependency still pins the vulnerable range — O3 confirms CVE-2021-22902 is resolved across your whole dependency graph.

How do I detect CVE-2021-22902 in my RubyGems dependencies?

Scan your dependency tree (package-lock.json, pnpm-lock.yaml, requirements.txt, go.sum, etc.) for actionpack, including transitive dependencies — a direct dependency you never call can still pull in a vulnerable version.

How do I mitigate CVE-2021-22902 if there is no patch (or I can't update yet)?

Cap what an attacker can consume: apply request size, rate and timeout limits in front of the affected component, and run it with memory and CPU limits so exhaustion degrades one worker rather than the whole service.

Is CVE-2021-22902 actively exploited in the wild?

Yes. There are 1 known exploit references for CVE-2021-22902, including 1 in-the-wild exploitation observed on GitHub and other sources. Treat this as actively exploitable and prioritize patching immediately. All exploit code should only be run in an isolated sandbox environment for research or authorized testing — never against production systems without explicit written authorization.

What is the EPSS score for CVE-2021-22902?

CVE-2021-22902 has an EPSS (Exploit Prediction Scoring System) score of 2.8%, placing it in the 86th percentile of all CVEs. EPSS is maintained by FIRST.org and estimates the probability that a vulnerability will be exploited in the wild within the next 30 days. This score indicates relatively lower exploitation probability, though the CVSS severity should still guide your patching priority.

What type of vulnerability is CVE-2021-22902?

CVE-2021-22902 is classified as Uncontrolled Resource Consumption (CWE-400). This weakness type describe the underlying flaw category, which helps determine the potential impact and the right class of mitigation.

When was CVE-2021-22902 published, and has it been updated?

CVE-2021-22902 was published on June 11, 2021 and was last updated on September 9, 2026. Advisory data evolves as severity scores, affected ranges, and exploit intelligence are revised — always check the latest version of the advisory before acting.

💎

💎 RubyGems

Not in CISA KEV

HIGH severity

CVE-2021-22902 — actionpack

HIGH

CVE-2021-22902 is a high-severity (CVSS 7.5) Uncontrolled Resource Consumption vulnerability in actionpack. 1 public exploit reference exists, so weaponization risk is real. A fix is available for actionpack — see the affected versions and patch details below.

Denial of Service in Action Dispatch

Also known asGHSA-g8ww-46x2-2p65

Published

Jun 11, 2021

Updated

Sep 9, 2026

Affected

2 pkgs

Patched

2 / 2

Exploits

1 known

Exploitation data as of Oct 9, 2026 · OSV.dev, NVD, FIRST.org (EPSS)

EPSS Exploitation Probability

via FIRST.org ↗

2.8%probability of exploitation in next 30 days

Lower Risk0.00%

Lower risk than most CVEs86th percentile — riskier than 86% of all scored CVEsHighest risk

Probability of exploitation in the next 30 days, from FIRST.org EPSS.

How urgent is this, really

CVE-2021-22902 by exploitation likelihood (EPSS) against impact (CVSS). Outside the shaded patch-first corner.

Where this sits among everything scored

Of 385,738 CVEs with a current EPSS score, this one falls in the < 10% band (highlighted). Counts from FIRST.org, log-scaled.

Real-World Exposure

2 pkgs affected

💎actionpack💎actionpack

Real-time download stats are indexed for npm and PyPI packages. This vulnerability affects RubyGems packages — download data is not available via public APIs for these ecosystems.

Description

Impact

There is a possible Denial of Service vulnerability in Action Dispatch. Carefully crafted Accept headers can cause the mime type parser in Action Dispatch to do catastrophic backtracking in the regular expression engine.

Releases

The fixed releases are available at the normal locations.

Workarounds

The following monkey patch placed in an initializer can be used to work around the issue.

module Mime
  class Type
    MIME_REGEXP = /\A(?:\*\/\*|#{MIME_NAME}\/(?:\*|#{MIME_NAME})(?>\s*#{MIME_PARAMETER}\s*)*)\z/
  end
end

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.

6-0-Prevent-catastrophic-backtracking-during-mime-parsin.patch - Patch for 6.0 series
6-1-Prevent-catastrophic-backtracking-during-mime-parsin.patch - Patch for 6.1 series

Please note that only the 6.1.Z, 6.0.Z, and 5.2.Z series are supported at present. 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.

Credits

Thanks to Security Curious [email protected] for reporting this!

Affected Packages

2 total 2 fixed

Ecosystem	Package	Vulnerable range	Fix
💎RubyGems	`actionpack`	≥ 6.0.0&&< 6.0.3.7	6.0.3.7`bundle update actionpack --conservative`
💎RubyGems	`actionpack`	≥ 6.1.0&&< 6.1.3.2	6.1.3.2`bundle update actionpack --conservative`

Affected Products

1 product · 2 configurations

Application

railsrubyonrails

≥ 6.1.0 && < 6.1.0.2

range

Exploits & PoCs

Research use only. For defensive security, authorized penetration testing, and academic research only. Never execute exploit code against systems without explicit written authorization.

The actionpack ruby gem (a framework for handling and responding to web …

discuss.rubyonrails.orgNVDAug 2021

Detection & mitigation playbook

Open-source dependency

Detect
Scan your dependency tree (package-lock.json, pnpm-lock.yaml, requirements.txt, go.sum, etc.) for actionpack, including transitive dependencies — a direct dependency you never call can still pull in a vulnerable version.
Fix
Update actionpack to 6.0.3.7 or later, then make sure no transitive (indirect) dependency still pins the vulnerable range — O3 confirms CVE-2021-22902 is resolved across your whole dependency graph.
Workarounds
Cap what an attacker can consume: apply request size, rate and timeout limits in front of the affected component, and run it with memory and CPU limits so exhaustion degrades one worker rather than the whole service.

Fixing This On Your OS

If you run this on a Linux distribution, patch through your package manager against the distro's own security advisory below — it tracks the exact backported fix for your release, which can ship on a different timeline (and sometimes a different severity) than the upstream project.

Red HatModerate

Product	Fixed in	Advisory
Red Hat Satellite 6.10 for RHEL 7	`tfm-rubygem-rails-0:6.0.3.7-1.el7sat`	RHSA-2021:4702

Frequently Asked Questions

Impact ------ There is a possible Denial of Service vulnerability in Action Dispatch. Carefully crafted Accept headers can cause the mime type parser in Action Dispatch to do catastrophic backtracking in the regular expression engine. Releases -------- The fixed releases are available at the normal locations. Workarounds ----------- The following monkey patch placed in an initializer can be used to work around the issue. ```ruby module Mime class Type MIME_REGEXP = /\A(?:\*\/\*|#{MIME_NAME}\/(?:\*|#{MIME_NAME})(?>\s*#{MIME_PARAMETER}\s*)*)\z/ end end ``` Patches ------- To aid user