HTTP Response Splitting (Early Hints) in Puma

MEDIO 6.5CVE-2020-5249 · GHSA-33vf-4xgg-9r58 · Published 02/03/2020 · updated 17/06/2026

Package	Affected versions	Patched versions
puma RubyGems	`≥ 4.0.0, < 4.3.3< 3.12.4`	`4.3.33.12.4`
puma puma	`≥ 4.0.0, ≤ 4.3.2≤ 3.12.3`	No fix yet

Description

Impact

If an application using Puma allows untrusted input in an early-hints header, an attacker can use a carriage return character 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-2020-5247, which fixed this vulnerability but only for regular responses.

Patches

This has been fixed in 4.3.3 and 3.12.4.

Workarounds

Users can not allow untrusted/user input in the Early Hints response header.

For more information

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NVD description

In Puma (RubyGem) before 4.3.3 and 3.12.4, if an application using Puma allows untrusted input in an early-hints header, an attacker can use a carriage return character 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-2020-5247, which fixed this vulnerability but only for regular responses. This has been fixed in 4.3.3 and 3.12.4.

References

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