CVE-2020-5249
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…
Does this matter?
Lower severity and a low EPSS score (1.57%). Track it; it rarely justifies an emergency change on its own.
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.
- CVSS 3.1
- 6.5 MEDIUMCVSS:3.1/AV:N/AC:L/PR:L/UI:N/S:U/C:N/I:H/A:N
- EPSS
- 1.57% probability · 75th percentile
- Public exploits
- None in Exploit-DB
- CISA KEV
- Not listed
- Weakness
- CWE-113, CWE-74
- Affected
- puma/puma
- Source
- security-advisories@github.com
EPSS 1.6% since 26 October 2026; no change recorded yet. Points are recorded when the score first appears and whenever it moves by a percentage point or more.
References
- https://github.com/puma/puma/commit/c22712fc93284a45a93f9ad7023888f3a65524f3Patch, Third Party Advisory
- https://github.com/puma/puma/security/advisories/GHSA-33vf-4xgg-9r58Third Party Advisory
- https://github.com/puma/puma/security/advisories/GHSA-84j7-475p-hp8vThird Party Advisory
- https://lists.fedoraproject.org/archives/list/package-announce%40lists.fedoraproject.org/message/BMJ3CGZ3DLBJ5WUUKMI5ZFXFJQMXJZIK/
- https://lists.fedoraproject.org/archives/list/package-announce%40lists.fedoraproject.org/message/DIHVO3CQMU7BZC7FCTSRJ33YDNS3GFPK/
- https://lists.fedoraproject.org/archives/list/package-announce%40lists.fedoraproject.org/message/NJ3LL5F5QADB6LM46GXZETREAKZMQNRD/
- https://owasp.org/www-community/attacks/HTTP_Response_SplittingThird Party Advisory
- https://github.com/puma/puma/commit/c22712fc93284a45a93f9ad7023888f3a65524f3Patch, Third Party Advisory
- https://github.com/puma/puma/security/advisories/GHSA-33vf-4xgg-9r58Third Party Advisory
- https://github.com/puma/puma/security/advisories/GHSA-84j7-475p-hp8vThird Party Advisory
- https://lists.fedoraproject.org/archives/list/package-announce%40lists.fedoraproject.org/message/BMJ3CGZ3DLBJ5WUUKMI5ZFXFJQMXJZIK/
- https://lists.fedoraproject.org/archives/list/package-announce%40lists.fedoraproject.org/message/DIHVO3CQMU7BZC7FCTSRJ33YDNS3GFPK/
- https://lists.fedoraproject.org/archives/list/package-announce%40lists.fedoraproject.org/message/NJ3LL5F5QADB6LM46GXZETREAKZMQNRD/
- https://owasp.org/www-community/attacks/HTTP_Response_SplittingThird Party Advisory
Source: NVD record, EPSS from FIRST.org, KEV from CISA, exploits from Exploit-DB. Refreshed daily. Download this record as JSON.