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CVE-2021-33621 — HTTP response splitting in cgi — CVE Details

HIGH

HTTP response splitting in CGI

Published November 19, 2022Updated August 13, 2026Source: osv

Summary

Ruby gem cgi.rb prior to versions 0.3.5, 0.2.2 and 0.1.0.2 allow HTTP header injection. If a CGI application using the CGI library inserts untrusted input into the HTTP response header, an attacker can exploit it to insert a newline character to split a header, and inject malicious content to deceive clients. This issue has been patched in versions 0.3.5, 0.2.2 and 0.1.0.2.

Advisory Timeline

  • First published November 19, 2022 (1423 days ago).
  • Last revised August 13, 2026 — 1364 days after initial publication.

Remediation

Upgrade to the fixed version using your package manager.

Bundler
Update cgi to 0.1.0.2 or later
gem install cgi -v 0.1.0.2
Bundler
Update cgi to 0.3.5 or later
gem install cgi -v 0.3.5
Bundler
Update cgi to 0.2.2 or later
gem install cgi -v 0.2.2

After upgrading, run your dependency scanner again to confirm the vulnerability is resolved.

Affected Packages (3)

Affects 1 ecosystem: rubygems (1).

PackageEcosystemAffectedFixed In
cgi
rubygems
0.1.0, 0.1.0.10.1.0.2
cgi
rubygems
0.3.0, 0.3.1, 0.3.2, 0.3.3 (+1 more)0.3.5
cgi
rubygems
0.2.0, 0.2.10.2.2

Vulnerability Classification

Common Weakness Enumeration (CWE) identifiers for this vulnerability type.

CVSS Score Breakdown

What the CVSS (Common Vulnerability Scoring System) 8.8 score means for each attack dimension.

Attack Vector
Network
Attack Complexity
Low
Privileges Required
Low
User Interaction
None
Scope
Unchanged
Confidentiality
High
Integrity
High
Availability
High

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

References

Frequently Asked Questions

What is CVE-2021-33621?
HTTP response splitting in CGI This vulnerability has been assigned a severity rating of HIGH (CVSS score: 8.8/10).
How do I check if my project is affected by CVE-2021-33621?
CVE-2021-33621 affects cgi. Use GeekWala's free vulnerability scanner to check your dependencies against CVE-2021-33621 and 200,000+ other known vulnerabilities.

Severity & Exploitability

CVSS Score
8.8

High exploitability or significant impact. Prioritize remediation within days.

Also Known As

GHSA-vc47-6rqg-c7f5
BIT-ruby-2021-33621
BIT-ruby-min-2021-33621

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