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CgiApplication · Ruby Lang

CVE-2025-27219

HIGH · 7.5 CVSS v3.1 Published 2025-03-04
Fix available
A fix is available. Upgrade to 0.3.5.1 / 0.4.2 or later.
See remediation →
84/100
Remediation priority · High
Remotely reachable No privileges Zero-click

Official description Straight from the sourceThe vendor's or NVD's own wording, published unedited. Authoritative, but often terse — it says what broke, rarely what to do.

NVD · unedited
In the CGI gem before 0.4.2 for Ruby, the CGI::Cookie.parse method in the CGI library contains a potential Denial of Service (DoS) vulnerability. The method does not impose any limit on the length of the raw cookie value it processes. This oversight can lead to excessive resource consumption when parsing extremely large cookies.

Technical summary Written by usOur analysis, written from the advisory, the CVSS vector and the affected-version data. It adds context the advisory leaves out, and never invents facts that are not in the source.

dbcve analysis · high confidence

The CGI::Cookie.parse method in the CGI gem for Ruby versions before 0.4.2 lacks input validation on cookie value lengths, allowing attackers to cause excessive resource consumption (DoS) by sending extremely large cookies that exhaust server resources during parsing.

MitigationUpgrade the CGI gem to version 0.4.2 or later which implements proper length limits on cookie value parsing to prevent resource exhaustion.

Verify against the referenced sources before acting — the references below are authoritative for this CVE, this summary is not.

Affected products & versions What the vendor confirmedThe version ranges the vendor confirmed as vulnerable. If your version sits inside a range here, treat yourself as exposed until you have upgraded.

NVD · CPE data
CgiApplication
Affected:< 0.3.5.1>= 0.4.0, < 0.4.2= 0.3.6

CVSS breakdown How the score is builtThe industry scoring standard. It rates how the flaw is reached, what it takes to exploit, and what an attacker gains — the score is derived from those, not the other way round.

From the vector
Attack vector
Network
Complexity
Low
Privileges
None
User interaction
None
Scope
Unchanged
Confidentiality
None
Integrity
None
Availability
High

CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:H

Am I affected? How to checkSteps we derive from the advisory and the affected-version data, so you can decide whether this CVE reaches your setup. They are a guide, not a scan — your own configuration is the authority.

dbcve checks

Work through these to decide whether this CVE applies to you.

  1. Check installed CGI gem version
    Run `gem list cgi` or add `puts Gem::Specification.find_by_name('cgi').version.to_s` to your Ruby application to see the installed version
    Affected if The version is < 0.3.5.1, = 0.3.6, or >= 0.4.0 but < 0.4.2
  2. Verify CGI cookie parsing is in use
    Search your codebase for calls to `CGI::Cookie.parse`, `CGI::Cookie.new`, or cookie handling via `cgi.cookies` or `env['HTTP_COOKIE']`
    Affected if Your application parses incoming HTTP cookies using the CGI gem's Cookie methods
  3. Check if application accepts external cookie input
    Inspect your web server configuration or application code to confirm it accepts and processes cookies from client requests (look for `CGI.new` instantiation handling HTTP requests)
    Affected if The application processes cookies from untrusted client requests, allowing attackers to send oversized cookie values
  4. Audit gemfile dependencies
    Check your Gemfile.lock for the `cgi` gem entry and its version constraint, or run `bundle exec gem specification cgi`
    Affected if The locked CGI gem version falls within the affected ranges

You are affected if your environment has the CGI gem installed at a vulnerable version AND your application processes HTTP cookies using CGI::Cookie.parse or related methods.

Generated from the published advisory. Verify against your own configuration.

Check your environment

Paste your version and any relevant configuration and it will be compared against the affected criteria above. Do not include secrets or credentials.

AI-assisted, checked against the advisory. Informational, not a guarantee.

Remediation Closing itWhat it takes to close this. Where a vendor fix exists we point at it; where none exists we say so plainly, and can build one. Effort estimates are scoped from the advisory, not from your codebase.

dbcve · scoped
Upgrade available Upgrade to 0.3.5.1 / 0.4.2 or later
Fixed in 0.3.5.10.4.2
Interim mitigation

Upgrade the CGI gem to version 0.4.2 or later which implements proper length limits on cookie value parsing to prevent resource exhaustion.

Recommended fix High confidence

CGI gem version 0.4.2 or later (or 0.3.5.1 for the 0.3.x branch)

  1. Identify the current version of the CGI gem in your project by running `gem list cgi` or checking your Gemfile
  2. For Ruby projects using Bundler, update the CGI gem by running `bundle update cgi` or manually change the version in your Gemfile to `gem 'cgi', '>= 0.4.2'`
  3. Run `bundle install` to install the updated gem
  4. Verify the upgrade was successful by running `gem list cgi` to confirm version 0.4.2 or higher is installed
  5. Test your application to ensure cookie parsing functionality works correctly after the update
Caveat Minimal risk - this is a bug fix for resource consumption; verify cookie handling in your application still works as expected after upgrade

Generated from the published advisory — verify against the referenced sources before acting.

Fix this in Cgi Scoped from the published advisory
  • Consultation1.0 h
  • Implementation2.0 h
  • Testing2.0 h
  • Review / QA1.0 h
6.0 hours of engineering $1,040
Get the upgrade done

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References Go to the primary sourcePrimary sources — vendor advisories, patches and trackers. Where our summary and a reference disagree, the reference wins.

Primary sources

Practitioner notes

Contributed

Peer-ranked notes from engineers who’ve handled CVE-2025-27219 in production — separate from our analysis above.

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What this is

A place for practitioners to share what actually worked: a mitigation you’ve tested, a configuration change, a version- or environment-specific caveat, or a link to a verified patch. The most useful notes rise to the top as peers upvote them, so the signal stays high.

What belongs here
  • Verified mitigations, workarounds, and config changes
  • Version or environment caveats, and links to real fixes
  • No weaponised exploit code, or anything meant to cause harm
  • No spam, self-promotion, credentials, or personal data