CVE-2020-8166: Actionpack Ability To Forge Per-form CSRF Vulnerability

MODERATE
Advisory Identifier: GHSA-jp5v-5gx4-jmj9
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CVSS 4.3
CWE-352
Published
Advisory Summary

CVE-2020-8166 is a MODERATE (CVSS 4.3) ability to forge per-form csrf vulnerability (CWE-352: Cross-Site Request Forgery (CSRF)) affecting Actionpack libraries in the RubyGems ecosystem. The issue involves ability to forge per-form csrf tokens in rails. Remediation is available by upgrading affected packages to version 5.2.4.3, 6.0.3.1.

CVE-2020-8166 at a Glance

CVE Identifier CVE-2020-8166
GHSA Identifier GHSA-jp5v-5gx4-jmj9
Severity MODERATE
CVSS v3.1 Base Score 4.3
CWE Classification CWE-352: Cross-Site Request Forgery (CSRF)
Affected Product Actionpack
Package Ecosystem RubyGems
Published Date
Last Updated

Security Impact

CVSS: 4.3

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

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

How to Fix CVE-2020-8166

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

actionpack fixed: 5.2.4.3 
Upgrade actionpack to 5.2.4.3
actionpack fixed: 6.0.3.1 
Upgrade actionpack to 6.0.3.1
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 actionpack

How to Check if You Are Affected

To determine whether your application is affected by CVE-2020-8166, inspect your project dependencies for Actionpack:

inspect dependencies for actionpack

Analyze the terminal output to locate any version of Actionpack in your dependency tree. If any resolved version matches the vulnerable ranges listed in the table below (for example, versions earlier than 5.2.4.3), 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-352: Cross-Site Request Forgery (CSRF), where the web application does not, or cannot, sufficiently verify whether a request was intentionally provided by the user who sent the request, which could have originated from an unauthorized actor. In Actionpack, 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

It is possible to, given a global CSRF token such as the one present in the authenticity_token meta tag, forge a per-form CSRF token for any action for that session. Impact ------ Given the ability to extract the global CSRF token, an attacker would be able to construct a per-form CSRF token for that session. Workarounds ----------- This is a low-severity security issue. As such, no workaround is necessarily until such time as the application can be upgraded.

CVE-2020-8166 Affected Actionpack Versions

2 component(s)
Fixed Versions:
5.2.4.36.0.3.1
Product / Package Ecosystem Affected Versions Fixed Version
actionpack
gem/actionpack
RubyGems
≥ 5.0.0
< 5.2.4.3
5.2.4.3
actionpack
gem/actionpack
RubyGems
≥ 6.0.0
< 6.0.3.1
6.0.3.1

References

NVD — CVE-2020-8166 NVD
https://nvd.nist.gov/vuln/detail/CVE-2020-8166
hackerone.com/reports/732415 WEB
https://hackerone.com/reports/732415
Actionpack Source Repository REPOSITORY
https://github.com/rails/rails
Actionpack Source Repository REPOSITORY
https://github.com/rubysec/ruby-advisory-db/blob/master/gems/actionpack/CVE-2020-8166.yml
groups.google.com/forum/ WEB
https://groups.google.com/forum/#!topic/rubyonrails-security/NOjKiGeXUgw
Actionpack Security Information SECURITY
https://groups.google.com/g/rubyonrails-security/c/NOjKiGeXUgw
Actionpack Security Information SECURITY
https://www.debian.org/security/2020/dsa-4766

Frequently Asked Questions

What is CVE-2020-8166?
CVE-2020-8166 is a security vulnerability in Actionpack involving Ability to forge per-form CSRF tokens in Rails under CWE-352: Cross-Site Request Forgery (CSRF).
Which Actionpack versions are affected?
Affected versions include releases prior to 5.2.4.3, 6.0.3.1 across affected packages: actionpack.
What version fixes CVE-2020-8166?
Upgrading to 5.2.4.3, 6.0.3.1 (or the latest patched release for your respective branch) resolves the vulnerability.
Is actionpack affected?
Yes, actionpack is affected in releases prior to 5.2.4.3, 6.0.3.1. Upgrade your dependency to 5.2.4.3, 6.0.3.1 or later.
What is the CVSS score of CVE-2020-8166?
CVE-2020-8166 has a CVSS v3.1 base score of 4.3 (MODERATE) with vector string CVSS:3.1/AV:N/AC:L/PR:N/UI:R/S:U/C:N/I:L/A:N.
What CWE is associated with CVE-2020-8166?
CVE-2020-8166 is classified under CWE-352: Cross-Site Request Forgery (CSRF) (The web application does not, or cannot, sufficiently verify whether a request was intentionally provided by the user who sent the request, which could have originated from an unauthorized actor.).
How can I check RubyGems dependencies for CVE-2020-8166?
Run the dependency tree command: 'inspect dependencies for actionpack'. 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-jp5v-5gx4-jmj9",
  "modified" : "2026-05-05T22:16:48Z",
  "published" : "2020-05-26T15:11:13Z",
  "aliases" : [ "CVE-2020-8166" ],
  "summary" : "Ability to forge per-form CSRF tokens in Rails",
  "details" : "It is possible to, given a global CSRF token such as the one present in the authenticity_token meta tag, forge a per-form CSRF token for any action for that session.\n\nImpact\n------\n\nGiven the ability to extract the global CSRF token, an attacker would be able to construct a per-form CSRF token for that session.\n\nWorkarounds\n-----------\n\nThis is a low-severity security issue. As such, no workaround is necessarily until such time as the application can be upgraded.",
  "severity" : [ {
    "type" : "CVSS_V3",
    "score" : "CVSS:3.1/AV:N/AC:L/PR:N/UI:R/S:U/C:N/I:L/A:N"
  } ],
  "affected" : [ {
    "package" : {
      "ecosystem" : "RubyGems",
      "name" : "actionpack"
    },
    "ranges" : [ {
      "type" : "ECOSYSTEM",
      "events" : [ {
        "introduced" : "5.0.0"
      }, {
        "fixed" : "5.2.4.3"
      } ]
    } ],
    "database_specific" : {
      "last_known_affected_version_range" : "<= 5.2.4.2"
    }
  }, {
    "package" : {
      "ecosystem" : "RubyGems",
      "name" : "actionpack"
    },
    "ranges" : [ {
      "type" : "ECOSYSTEM",
      "events" : [ {
        "introduced" : "6.0.0"
      }, {
        "fixed" : "6.0.3.1"
      } ]
    } ],
    "database_specific" : {
      "last_known_affected_version_range" : "<= 6.0.3"
    }
  } ],
  "references" : [ {
    "type" : "ADVISORY",
    "url" : "https://nvd.nist.gov/vuln/detail/CVE-2020-8166"
  }, {
    "type" : "WEB",
    "url" : "https://hackerone.com/reports/732415"
  }, {
    "type" : "PACKAGE",
    "url" : "https://github.com/rails/rails"
  }, {
    "type" : "WEB",
    "url" : "https://github.com/rubysec/ruby-advisory-db/blob/master/gems/actionpack/CVE-2020-8166.yml"
  }, {
    "type" : "WEB",
    "url" : "https://groups.google.com/forum/#!topic/rubyonrails-security/NOjKiGeXUgw"
  }, {
    "type" : "WEB",
    "url" : "https://groups.google.com/g/rubyonrails-security/c/NOjKiGeXUgw"
  }, {
    "type" : "WEB",
    "url" : "https://www.debian.org/security/2020/dsa-4766"
  } ],
  "database_specific" : {
    "cwe_ids" : [ "CWE-352" ],
    "severity" : "MODERATE",
    "github_reviewed" : true,
    "github_reviewed_at" : "2020-05-26T15:10:56Z",
    "nvd_published_at" : "2020-07-02T19:15:12Z"
  }
}