CVE-2021-22904Public exploitNetwork attack vector

Service interruption via slow token-header regex

Published Jun 11, 2021 · Updated Aug 3, 2024

Denial of service in affected Rails Action Pack releases allows remote attackers to interrupt service via crafted Authorization headers. ActionController::HttpAuthentication::Token uses AUTHN_PAIR_DELIMITERS with a quantified tab alternative, causing slow regex processing on long malformed token headers. Only applications that invoke authenticate_or_request_with_http_token or authenticate_with_http_token for request authentication are exposed; repeated unauthenticated requests can occupy workers and interrupt service.

CVSS severity7.5
High
EPSS probability5.00%
Next 30 days · Sep 16, 2026
Known exploitationUnconfirmed
Based on sourced intelligence
Hinoki checkNot available
Coverage for this vulnerability

See if you're affected

Explore vulnerability checks for your environment with Hinoki.

Book a demo

Summary

What happened

Denial of service in affected Rails Action Pack releases allows remote attackers to interrupt service via crafted Authorization headers. ActionController::HttpAuthentication::Token uses AUTHN_PAIR_DELIMITERS with a quantified tab alternative, causing slow regex processing on long malformed token headers. Only applications that invoke authenticate_or_request_with_http_token or authenticate_with_http_token for request authentication are exposed; repeated unauthenticated requests can occupy workers and interrupt service.

The record

CVE
CVE-2021-22904
Published
Jun 11, 2021
Updated
Aug 3, 2024
Vendor
Rails
Product
Action Pack
Classifications
CWE-400, T1499.003
Attack vector
network
Privileges
unauthenticated

Timeline

How it unfolded

  1. Jun 11, 2021CVE publishedPublication date reported by the CVE source.
  2. Aug 3, 2024Record updatedLatest update available in the CVE record.

Exploitability

Present is not the same as exploitable

Compare your product and version with the public record. A matching version still requires validation against your environment.

Is a vulnerable build present?

Compare these published version ranges with your installed build and any vendor patches.

  1. Affected versionversion=Fixed in 6.1.3.2, 6.0.3.7, 5.2.4.6, 5.2.6

What conditions does exploitation require?

Attack vectornetwork
Required privilegesunauthenticated

What is affected?

Rails · Action Packversion=Fixed in 6.1.3.2, 6.0.3.7, 5.2.4.6, 5.2.6

Published CVSS scores

7.5NIST NVDCVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:H
5.0NIST NVDAV:N/AC:L/Au:N/C:N/I:N/A:P
7.5GitHub Advisory DatabaseCVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:H

CVSS describes severity. EPSS estimates exploitation probability.

Attacks

What attackers are doing with it

Daily unique IPs observed by Shadowserver honeypots for known exploited vulnerabilities (KEVs). Missing observations do not establish an absence of attacks.

Daily unique IPsNo honeypot observations are available for this CVE in the selected window.

No observations available

Sep 10, 2026Sep 16, 2026
Latest reporting daySep 16, 2026
Latest daily unique IPsUnavailable
Prior 30-day averageUnavailable
SourceShadowserver honeypots (KEV)
Vectornetwork
Privilegesunauthenticated
Known exploitationUnconfirmed
Public exploitPublished

Weakness, pattern, technique

CWE-400Uncontrolled Resource Consumption
T1499.003Application Exhaustion Flood

Public exploit references

Labels summarize the accepted research assessment. They do not indicate a test against your environment.

Technologies

Your stack

See the directory against your own environment.

Your stack

Check the software in your environment

Book a demo to see how Hinoki identifies affected software and validates exploitability in your environment.

Book a demo