CVE-2026-33169: Activesupport Denial of Service Vulnerability

MODERATE
Advisory Identifier: GHSA-cg4j-q9v8-6v38
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CWE-400 CWE-1333
Published
Advisory Summary

CVE-2026-33169 is a MODERATE denial of service vulnerability (CWE-400: Uncontrolled Resource Consumption) affecting Activesupport libraries in the RubyGems ecosystem. The issue involves rails active support has a possible redos vulnerability in number_to_delimited. Remediation is available by upgrading affected packages to version 8.1.2.1, 8.0.4.1, 7.2.3.1.

CVE-2026-33169 at a Glance

CVE Identifier CVE-2026-33169
GHSA Identifier GHSA-cg4j-q9v8-6v38
Severity MODERATE
CVSS v3.1 Base Score N/A
CWE Classification CWE-400: Uncontrolled Resource Consumption
Affected Product Activesupport
Package Ecosystem RubyGems
Published Date
Last Updated

How to Fix CVE-2026-33169

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

activesupport fixed: 8.1.2.1 
Upgrade activesupport to 8.1.2.1
activesupport fixed: 8.0.4.1 
Upgrade activesupport to 8.0.4.1
activesupport fixed: 7.2.3.1 
Upgrade activesupport to 7.2.3.1
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 activesupport

How to Check if You Are Affected

To determine whether your application is affected by CVE-2026-33169, inspect your project dependencies for Activesupport:

inspect dependencies for activesupport

Analyze the terminal output to locate any version of Activesupport in your dependency tree. If any resolved version matches the vulnerable ranges listed in the table below (for example, versions earlier than 8.1.2.1), 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-400: Uncontrolled Resource Consumption, where the product does not properly control the allocation and maintenance of a limited resource. In Activesupport, 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

### Impact `NumberToDelimitedConverter` used a regular expression with `gsub!` to insert thousands delimiters. This could produce quadratic time complexity on long digit strings. ### Releases The fixed releases are available at the normal locations. ### Credit This issue was responsibly reported by Hackerone researcher [scyoon](https://hackerone.com/scyoon).

CVE-2026-33169 Affected Activesupport Versions

3 component(s)
Fixed Versions:
8.1.2.18.0.4.17.2.3.1
Product / Package Ecosystem Affected Versions Fixed Version
activesupport
gem/activesupport
RubyGems
≥ 8.1.0.beta1
< 8.1.2.1
8.1.2.1
activesupport
gem/activesupport
RubyGems
≥ 8.0.0.beta1
< 8.0.4.1
8.0.4.1
activesupport
gem/activesupport
RubyGems
< 7.2.3.1
7.2.3.1

References

GitHub Advisory / Wiki ADVISORY
https://github.com/rails/rails/security/advisories/GHSA-cg4j-q9v8-6v38
NVD — CVE-2026-33169 NVD
https://nvd.nist.gov/vuln/detail/CVE-2026-33169
Security Fix Commit FIX COMMIT
https://github.com/rails/rails/commit/29154f1097da13d48fdb3200760b3e3da66dcb11
Security Fix Commit FIX COMMIT
https://github.com/rails/rails/commit/b54a4b373c6f042cab6ee2033246b1c9ecc38974
Security Fix Commit FIX COMMIT
https://github.com/rails/rails/commit/ec1a0e215efd27a3b3911aae6df978a80f456a49
Activesupport Source Repository REPOSITORY
https://github.com/rails/rails
Activesupport Release RELEASE
https://github.com/rails/rails/releases/tag/v7.2.3.1
Activesupport Release RELEASE
https://github.com/rails/rails/releases/tag/v8.0.4.1
Activesupport Release RELEASE
https://github.com/rails/rails/releases/tag/v8.1.2.1
Activesupport Source Repository REPOSITORY
https://github.com/rubysec/ruby-advisory-db/blob/master/gems/activesupport/CVE-2026-33169.yml

Frequently Asked Questions

What is CVE-2026-33169?
CVE-2026-33169 is a security vulnerability in Activesupport involving Rails Active Support has a possible ReDoS vulnerability in number_to_delimited under CWE-400: Uncontrolled Resource Consumption.
Which Activesupport versions are affected?
Affected versions include releases prior to 8.1.2.1, 8.0.4.1, 7.2.3.1 across affected packages: activesupport.
What version fixes CVE-2026-33169?
Upgrading to 8.1.2.1, 8.0.4.1, 7.2.3.1 (or the latest patched release for your respective branch) resolves the vulnerability.
Is activesupport affected?
Yes, activesupport is affected in releases prior to 8.1.2.1, 8.0.4.1, 7.2.3.1. Upgrade your dependency to 8.1.2.1, 8.0.4.1, 7.2.3.1 or later.
What CWE is associated with CVE-2026-33169?
CVE-2026-33169 is classified under CWE-400: Uncontrolled Resource Consumption (The product does not properly control the allocation and maintenance of a limited resource.).
How can I check RubyGems dependencies for CVE-2026-33169?
Run the dependency tree command: 'inspect dependencies for activesupport'. 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-cg4j-q9v8-6v38",
  "modified" : "2026-05-13T16:15:32Z",
  "published" : "2026-03-23T20:52:40Z",
  "aliases" : [ "CVE-2026-33169" ],
  "summary" : "Rails Active Support has a possible ReDoS vulnerability in number_to_delimited",
  "details" : "### Impact\n`NumberToDelimitedConverter` used a regular expression with `gsub!` to insert thousands delimiters. This could produce quadratic time complexity on long digit strings.\n\n### Releases\nThe fixed releases are available at the normal locations.\n\n### Credit\nThis issue was responsibly reported by Hackerone researcher [scyoon](https://hackerone.com/scyoon).",
  "severity" : [ {
    "type" : "CVSS_V4",
    "score" : "CVSS:4.0/AV:N/AC:L/AT:N/PR:N/UI:N/VC:N/VI:N/VA:L/SC:N/SI:N/SA:N"
  } ],
  "affected" : [ {
    "package" : {
      "ecosystem" : "RubyGems",
      "name" : "activesupport"
    },
    "ranges" : [ {
      "type" : "ECOSYSTEM",
      "events" : [ {
        "introduced" : "8.1.0.beta1"
      }, {
        "fixed" : "8.1.2.1"
      } ]
    } ]
  }, {
    "package" : {
      "ecosystem" : "RubyGems",
      "name" : "activesupport"
    },
    "ranges" : [ {
      "type" : "ECOSYSTEM",
      "events" : [ {
        "introduced" : "8.0.0.beta1"
      }, {
        "fixed" : "8.0.4.1"
      } ]
    } ]
  }, {
    "package" : {
      "ecosystem" : "RubyGems",
      "name" : "activesupport"
    },
    "ranges" : [ {
      "type" : "ECOSYSTEM",
      "events" : [ {
        "introduced" : "0"
      }, {
        "fixed" : "7.2.3.1"
      } ]
    } ]
  } ],
  "references" : [ {
    "type" : "WEB",
    "url" : "https://github.com/rails/rails/security/advisories/GHSA-cg4j-q9v8-6v38"
  }, {
    "type" : "ADVISORY",
    "url" : "https://nvd.nist.gov/vuln/detail/CVE-2026-33169"
  }, {
    "type" : "WEB",
    "url" : "https://github.com/rails/rails/commit/29154f1097da13d48fdb3200760b3e3da66dcb11"
  }, {
    "type" : "WEB",
    "url" : "https://github.com/rails/rails/commit/b54a4b373c6f042cab6ee2033246b1c9ecc38974"
  }, {
    "type" : "WEB",
    "url" : "https://github.com/rails/rails/commit/ec1a0e215efd27a3b3911aae6df978a80f456a49"
  }, {
    "type" : "PACKAGE",
    "url" : "https://github.com/rails/rails"
  }, {
    "type" : "WEB",
    "url" : "https://github.com/rails/rails/releases/tag/v7.2.3.1"
  }, {
    "type" : "WEB",
    "url" : "https://github.com/rails/rails/releases/tag/v8.0.4.1"
  }, {
    "type" : "WEB",
    "url" : "https://github.com/rails/rails/releases/tag/v8.1.2.1"
  }, {
    "type" : "WEB",
    "url" : "https://github.com/rubysec/ruby-advisory-db/blob/master/gems/activesupport/CVE-2026-33169.yml"
  } ],
  "database_specific" : {
    "cwe_ids" : [ "CWE-1333", "CWE-400" ],
    "severity" : "MODERATE",
    "github_reviewed" : true,
    "github_reviewed_at" : "2026-03-23T20:52:40Z",
    "nvd_published_at" : "2026-03-24T00:16:28Z"
  }
}