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CVE-2020-5247 — HTTP Response Splitting in puma — CVE Details

MEDIUM

HTTP Response Splitting in Puma

Published February 28, 2020Updated July 8, 2026Source: osv

Summary

In Puma (RubyGem) before 4.3.2 and 3.12.3, if an application using Puma allows untrusted input in a response header, an attacker can use newline characters (i.e. `CR`, `LF` or`/r`, `/n`) to end the header and inject malicious content, such as additional headers or an entirely new response body. This vulnerability is known as HTTP Response Splitting. While not an attack in itself, response splitting is a vector for several other attacks, such as cross-site scripting (XSS). This is related to CVE-2019-16254, which fixed this vulnerability for the WEBrick Ruby web server. This has been fixed in versions 4.3.2 and 3.12.3 by checking all headers for line endings and rejecting headers with those characters.

Advisory Timeline

  • First published February 28, 2020 (2418 days ago).
  • Last revised July 8, 2026 — 2322 days after initial publication.

Remediation

Upgrade to the fixed version using your package manager.

Bundler
Update puma to 4.3.3 or later
gem install puma -v 4.3.3
Bundler
Update puma to 3.12.4 or later
gem install puma -v 3.12.4

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

Affected Packages (2)

Affects 1 ecosystem: rubygems (1).

PackageEcosystemAffectedFixed In
puma
rubygems
4.0.0, 4.0.1, 4.1.0, 4.1.1 (+4 more)4.3.3
puma
rubygems
0.8.0, 0.8.1, 0.8.2, 0.9.0 (+102 more)3.12.4

Vulnerability Classification

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

CVSS Score Breakdown

What the CVSS (Common Vulnerability Scoring System) 6.5 score means for each attack dimension.

Attack Vector
Network
Attack Complexity
Low
Privileges Required
Low
User Interaction
Required
Scope
Changed
Confidentiality
Low
Integrity
Low
Availability
Low

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

References

Frequently Asked Questions

What is CVE-2020-5247?
HTTP Response Splitting in Puma This vulnerability has been assigned a severity rating of MEDIUM (CVSS score: 6.5/10).
How do I check if my project is affected by CVE-2020-5247?
CVE-2020-5247 affects puma. Use GeekWala's free vulnerability scanner to check your dependencies against CVE-2020-5247 and 200,000+ other known vulnerabilities.

Severity & Exploitability

CVSS Score
6.5

Exploitation requires specific conditions or has limited impact. Remediate within weeks.

Also Known As

GHSA-84j7-475p-hp8v
BIT-ruby-2020-5247
BIT-ruby-min-2020-5247

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