CVE-2021-22904: Possible DoS Vulnerability in Action Controller Token Authentication

Severity: high (CVSS 7.5 v3.1)
Exploited in the wild: not listed in CISA KEV
EPSS: 4.9% probability of exploitation in the next 30 days
Public exploit or detection template: yes
Published: 2021-06-11 · updated 2026-06-17
Weakness: CWE-400

Description

The actionpack ruby gem before 6.1.3.2, 6.0.3.7, 5.2.4.6, 5.2.6 suffers from a possible denial of service vulnerability in the Token Authentication logic in Action Controller due to a too permissive regular expression. Impacted code uses `authenticate_or_request_with_http_token` or `authenticate_with_http_token` for request authentication.

Affected products

Ruby on Rails: before 5.2.4.6; from 5.2.5 before 5.2.6; from 6.0.0 before 6.0.3.7; from 6.1.0 before 6.1.3.2 — fixed in 5.2.4.6, 5.2.6, 6.0.3.7, 6.1.3.2
Rubygems Actionpack: from 6.0.0 before 6.0.3.7; from 6.1.0 before 6.1.3.2; from 5.2.5 before 5.2.6; from 4.0.0 before 5.2.4.6; 6.0.0, 6.0.1, 6.0.1.rc1, 6.0.2, 6.0.2.1, 6.0.2.2 (+188) — fixed in 6.0.3.7, 6.1.3.2, 5.2.6, 5.2.4.6

How to fix

Upgrade to a fixed version: Ruby on Rails 5.2.4.6, 5.2.6, 6.0.3.7, 6.1.3.2; Rubygems Actionpack 6.0.3.7, 6.1.3.2, 5.2.6, 5.2.4.6. Check the vendor advisory for mitigations.

References

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