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  5. CVE-2020-8166

CVE-2020-8166: Ability to forge per-form CSRF tokens in Rails

May 26, 2020 (updated May 5, 2026)

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.

References

  • github.com/advisories/GHSA-jp5v-5gx4-jmj9
  • github.com/rails/rails
  • github.com/rubysec/ruby-advisory-db/blob/master/gems/actionpack/CVE-2020-8166.yml
  • groups.google.com/forum/
  • groups.google.com/g/rubyonrails-security/c/NOjKiGeXUgw
  • hackerone.com/reports/732415
  • nvd.nist.gov/vuln/detail/CVE-2020-8166
  • www.debian.org/security/2020/dsa-4766

Code Behaviors & Features

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Affected versions

All versions starting from 5.0.0 before 5.2.4.3, all versions starting from 6.0.0 before 6.0.3.1

Fixed versions

  • 5.2.4.3
  • 6.0.3.1

Solution

Upgrade to versions 5.2.4.3, 6.0.3.1 or above.

Impact 4.3 MEDIUM

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

Learn more about CVSS

Weakness

  • CWE-352: Cross-Site Request Forgery (CSRF)

Source file

gem/actionpack/CVE-2020-8166.yml

Spotted a mistake? Edit the file on GitLab.

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