{"cve":"CVE-2020-5247","nvd":{"published":"2020-02-28T17:15:12.220","modified":"2026-06-17T03:21:07.497","status":"Modified","description":"In Puma (RubyGem) before 4.3.2 and before 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.","cvss_v4":null,"cvss_v3":{"version":"3.1","vector":"CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:H/A:N","score":7.5},"cwes":["CWE-74","CWE-113"],"references":["https://github.com/puma/puma/security/advisories/GHSA-84j7-475p-hp8v","https://lists.debian.org/debian-lts-announce/2022/05/msg00034.html","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/"],"products":["debian:debian_linux","fedoraproject:fedora","puma:puma","ruby-lang:ruby"],"source":"nvd","synced_at":"2026-10-19T21:02:53.949909883+00:00"},"epss":{"cve":"CVE-2020-5247","score":0.02549,"percentile":0.85027,"date":"2026-10-31"},"kev":null,"osv":[{"id":"GHSA-84j7-475p-hp8v","url":"https://osv.dev/vulnerability/GHSA-84j7-475p-hp8v","summary":"HTTP Response Splitting in Puma","modified":"2026-07-08T06:27:02.150553465Z","packages":[{"ecosystem":"RubyGems","name":"puma","purl":"pkg:gem/puma","ranges":["<3.12.4"],"fixed":["3.12.4"]},{"ecosystem":"RubyGems","name":"puma","purl":"pkg:gem/puma","ranges":[">=4.0.0 <4.3.3"],"fixed":["4.3.3"]}]}],"attribution":["This product uses the NVD API but is not endorsed or certified by the NVD.","EPSS scores: FIRST Exploit Prediction Scoring System, https://www.first.org/epss","Known exploited vulnerabilities: CISA Known Exploited Vulnerabilities Catalog, https://www.cisa.gov/known-exploited-vulnerabilities-catalog","Package advisories: OSV (https://osv.dev), from the GitHub Advisory Database, PyPA, Go, RustSec and other ecosystem databases, under CC-BY 4.0 or CC0","CVE records: the CVE Program's CVE List (https://www.cve.org), under its terms of use (https://www.cve.org/Legal/TermsOfUse). CVE is a registered trademark of The MITRE Corporation; this product is not affiliated with the CVE Program."]}