CVE-2025-27220: Cgi Denial of Service Vulnerability

MODERATE
Advisory Identifier: GHSA-mhwm-jh88-3gjf
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CVSS 4.0
CWE-1333
Published
Advisory Summary

CVE-2025-27220 is a MODERATE (CVSS 4.0) denial of service vulnerability (CWE-1333: Inefficient Regular Expression Complexity) affecting Cgi libraries in the RubyGems ecosystem. The issue involves cgi has regular expression denial of service (redos) potential in util#escapeelement. Remediation is available by upgrading affected packages to version 0.3.5.1, 0.3.7, 0.4.2.

CVE-2025-27220 at a Glance

CVE Identifier CVE-2025-27220
GHSA Identifier GHSA-mhwm-jh88-3gjf
Severity MODERATE
CVSS v3.1 Base Score 4.0
CWE Classification CWE-1333: Inefficient Regular Expression Complexity
Affected Product Cgi
Package Ecosystem RubyGems
Published Date
Last Updated

Security Impact

CVSS: 4.0

The security impact metrics below are parsed directly from the CVSS v3.1 vector string (CVSS:3.1/AV:N/AC:H/PR:N/UI:N/S:C/C:N/I:N/A:L).

Attack Vector Network (AV:N)
Attack Complexity High (AC:H)
Privileges Required None (PR:N)
User Interaction None (UI:N)
Scope Changed (S:C)
Confidentiality None (C:N)
Integrity None (I:N)
Availability Low (A:L)

How to Fix CVE-2025-27220

To remediate this vulnerability, upgrade all affected Cgi dependencies to a patched release. Both direct and transitive dependencies should be checked, as frameworks or security libraries may pull in vulnerable versions transitively.

cgi fixed: 0.3.5.1 
Upgrade cgi to 0.3.5.1
cgi fixed: 0.3.7 
Upgrade cgi to 0.3.7
cgi fixed: 0.4.2 
Upgrade cgi to 0.4.2
Verify Direct and Transitive Dependencies

Run the following command in your project directory to verify that all resolved dependencies use the patched release: 

inspect dependencies for cgi

How to Check if You Are Affected

To determine whether your application is affected by CVE-2025-27220, inspect your project dependencies for Cgi:

inspect dependencies for cgi

Analyze the terminal output to locate any version of Cgi in your dependency tree. If any resolved version matches the vulnerable ranges listed in the table below (for example, versions earlier than 0.3.5.1), your application is affected.

Note: Verify declared build manifests and deployed runtime container environments.

Technical Details

Vulnerability Mechanism & Technical Analysis

This vulnerability is classified under CWE-1333: Inefficient Regular Expression Complexity, where the product uses a regular expression with a worst-case computational complexity that is inefficient and possibly exponential. In Cgi, software state validation or input boundaries are circumvented during processing. Review the official source advisory statement below for specific affected components, classes, and reproduction details.

Source Advisory Statement

There is a possibility for Regular expression Denial of Service (ReDoS) by in the cgi gem. This vulnerability has been assigned the CVE identifier CVE-2025-27220. We recommend upgrading the cgi gem. ## Details The regular expression used in `CGI::Util#escapeElement` is vulnerable to ReDoS. The crafted input could lead to a high CPU consumption. This vulnerability only affects Ruby 3.1 and 3.2. If you are using these versions, please update CGI gem to version 0.3.5.1, 0.3.7, 0.4.2 or later. ## Affected versions cgi gem versions <= 0.3.5, 0.3.6, 0.4.0 and 0.4.1. ## Credits Thanks to svalkanov for discovering this issue. Also thanks to nobu for fixing this vulnerability.

CVE-2025-27220 Affected Cgi Versions

3 component(s)
Fixed Versions:
0.3.5.10.3.70.4.2
Product / Package Ecosystem Affected Versions Fixed Version
cgi
gem/cgi
RubyGems
< 0.3.5.1
0.3.5.1
cgi
gem/cgi
RubyGems
≥ 0.3.6
< 0.3.7
All 1 versions
0.3.6
0.3.7
cgi
gem/cgi
RubyGems
≥ 0.4.0
< 0.4.2
0.4.2

References

NVD — CVE-2025-27220 NVD
https://nvd.nist.gov/vuln/detail/CVE-2025-27220
Cgi Source Repository REPOSITORY
https://github.com/ruby/cgi/pull/52
Cgi Source Repository REPOSITORY
https://github.com/ruby/cgi/pull/53
Cgi Source Repository REPOSITORY
https://github.com/ruby/cgi/pull/54
hackerone.com/reports/2890322 WEB
https://hackerone.com/reports/2890322
Cgi Source Repository REPOSITORY
https://github.com/ruby/cgi
Cgi Source Repository REPOSITORY
https://github.com/rubysec/ruby-advisory-db/blob/master/gems/cgi/CVE-2025-27220.yml
lists.debian.org/debian-lts-announce... WEB
https://lists.debian.org/debian-lts-announce/2025/03/msg00008.html
CVE Official Record — CVE-2025-27220 CVE
https://www.cve.org/CVERecord?id=CVE-2025-27220
Cgi Security Information SECURITY
https://www.ruby-lang.org/en/news/2025/02/26/security-advisories

Frequently Asked Questions

What is CVE-2025-27220?
CVE-2025-27220 is a security vulnerability in Cgi involving CGI has Regular Expression Denial of Service (ReDoS) potential in Util#escapeElement under CWE-1333: Inefficient Regular Expression Complexity.
Which Cgi versions are affected?
Affected versions include releases prior to 0.3.5.1, 0.3.7, 0.4.2 across affected packages: cgi.
What version fixes CVE-2025-27220?
Upgrading to 0.3.5.1, 0.3.7, 0.4.2 (or the latest patched release for your respective branch) resolves the vulnerability.
Is cgi affected?
Yes, cgi is affected in releases prior to 0.3.5.1, 0.3.7, 0.4.2. Upgrade your dependency to 0.3.5.1, 0.3.7, 0.4.2 or later.
What is the CVSS score of CVE-2025-27220?
CVE-2025-27220 has a CVSS v3.1 base score of 4.0 (MODERATE) with vector string CVSS:3.1/AV:N/AC:H/PR:N/UI:N/S:C/C:N/I:N/A:L.
What CWE is associated with CVE-2025-27220?
CVE-2025-27220 is classified under CWE-1333: Inefficient Regular Expression Complexity (The product uses a regular expression with a worst-case computational complexity that is inefficient and possibly exponential.).
How can I check RubyGems dependencies for CVE-2025-27220?
Run the dependency tree command: 'inspect dependencies for cgi'. This command lists direct and transitive dependencies in your build configuration so you can verify if a vulnerable version is resolved.
Machine-readable OSV JSON OSV v1.5 Schema
Normalized schema output
View Raw JSON 
{
  "schema_version" : "1.4.0",
  "id" : "GHSA-mhwm-jh88-3gjf",
  "modified" : "2025-11-04T00:32:21Z",
  "published" : "2025-03-03T22:05:08Z",
  "aliases" : [ "CVE-2025-27220" ],
  "summary" : "CGI has Regular Expression Denial of Service (ReDoS) potential in Util#escapeElement",
  "details" : "There is a possibility for Regular expression Denial of Service (ReDoS) by in the cgi gem. This vulnerability has been assigned the CVE identifier CVE-2025-27220. We recommend upgrading the cgi gem.\n\n## Details\n\nThe regular expression used in `CGI::Util#escapeElement` is vulnerable to ReDoS. The crafted input could lead to a high CPU consumption.\n\nThis vulnerability only affects Ruby 3.1 and 3.2. If you are using these versions, please update CGI gem to version 0.3.5.1, 0.3.7, 0.4.2 or later.\n\n## Affected versions\n\ncgi gem versions <= 0.3.5, 0.3.6, 0.4.0 and 0.4.1.\n\n## Credits\n\nThanks to svalkanov for discovering this issue.\nAlso thanks to nobu for fixing this vulnerability.",
  "severity" : [ {
    "type" : "CVSS_V3",
    "score" : "CVSS:3.1/AV:N/AC:H/PR:N/UI:N/S:C/C:N/I:N/A:L"
  }, {
    "type" : "CVSS_V4",
    "score" : "CVSS:4.0/AV:N/AC:H/AT:P/PR:N/UI:N/VC:N/VI:N/VA:L/SC:N/SI:N/SA:N"
  } ],
  "affected" : [ {
    "package" : {
      "ecosystem" : "RubyGems",
      "name" : "cgi"
    },
    "ranges" : [ {
      "type" : "ECOSYSTEM",
      "events" : [ {
        "introduced" : "0"
      }, {
        "fixed" : "0.3.5.1"
      } ]
    } ]
  }, {
    "package" : {
      "ecosystem" : "RubyGems",
      "name" : "cgi"
    },
    "ranges" : [ {
      "type" : "ECOSYSTEM",
      "events" : [ {
        "introduced" : "0.3.6"
      }, {
        "fixed" : "0.3.7"
      } ]
    } ],
    "versions" : [ "0.3.6" ]
  }, {
    "package" : {
      "ecosystem" : "RubyGems",
      "name" : "cgi"
    },
    "ranges" : [ {
      "type" : "ECOSYSTEM",
      "events" : [ {
        "introduced" : "0.4.0"
      }, {
        "fixed" : "0.4.2"
      } ]
    } ]
  } ],
  "references" : [ {
    "type" : "ADVISORY",
    "url" : "https://nvd.nist.gov/vuln/detail/CVE-2025-27220"
  }, {
    "type" : "WEB",
    "url" : "https://github.com/ruby/cgi/pull/52"
  }, {
    "type" : "WEB",
    "url" : "https://github.com/ruby/cgi/pull/53"
  }, {
    "type" : "WEB",
    "url" : "https://github.com/ruby/cgi/pull/54"
  }, {
    "type" : "WEB",
    "url" : "https://hackerone.com/reports/2890322"
  }, {
    "type" : "PACKAGE",
    "url" : "https://github.com/ruby/cgi"
  }, {
    "type" : "WEB",
    "url" : "https://github.com/rubysec/ruby-advisory-db/blob/master/gems/cgi/CVE-2025-27220.yml"
  }, {
    "type" : "WEB",
    "url" : "https://lists.debian.org/debian-lts-announce/2025/03/msg00008.html"
  }, {
    "type" : "WEB",
    "url" : "https://www.cve.org/CVERecord?id=CVE-2025-27220"
  }, {
    "type" : "WEB",
    "url" : "https://www.ruby-lang.org/en/news/2025/02/26/security-advisories"
  } ],
  "database_specific" : {
    "cwe_ids" : [ "CWE-1333" ],
    "severity" : "MODERATE",
    "github_reviewed" : true,
    "github_reviewed_at" : "2025-03-03T22:05:08Z",
    "nvd_published_at" : "2025-03-04T00:15:31Z"
  }
}