{"cve":"CVE-2021-41136","nvd":{"published":"2021-10-12T16:15:07.630","modified":"2026-06-17T04:07:56.800","status":"Modified","description":"Puma is a HTTP 1.1 server for Ruby/Rack applications. Prior to versions 5.5.1 and 4.3.9, using `puma` with a proxy which forwards HTTP header values which contain the LF character could allow HTTP request smugggling. A client could smuggle a request through a proxy, causing the proxy to send a response back to another unknown client. The only proxy which has this behavior, as far as the Puma team is aware of, is Apache Traffic Server. If the proxy uses persistent connections and the client adds another request in via HTTP pipelining, the proxy may mistake it as the first request's body. Puma, however, would see it as two requests, and when processing the second request, send back a response that the proxy does not expect. If the proxy has reused the persistent connection to Puma to send another request for a different client, the second response from the first client will be sent to the second client. This vulnerability was patched in Puma 5.5.1 and 4.3.9. As a workaround, do not use Apache Traffic Server with `puma`.","cvss_v4":null,"cvss_v3":{"version":"3.1","vector":"CVSS:3.1/AV:N/AC:H/PR:L/UI:R/S:U/C:L/I:L/A:N","score":3.7},"cwes":["CWE-444"],"references":["https://github.com/puma/puma/commit/436c71807f00e07070902a03f79fd3e130eb6b18","https://github.com/puma/puma/commit/acdc3ae571dfae0e045cf09a295280127db65c7f","https://github.com/puma/puma/commit/fb6ad8f8013ab5cdbb2f444cbfabd0b4fde71139","https://github.com/puma/puma/security/advisories/GHSA-48w2-rm65-62xx","https://github.com/puma/puma/commit/acdc3ae571dfae0e045cf09a295280127db65c7f"],"products":["debian:debian_linux","puma:puma"],"source":"nvd","synced_at":"2026-10-19T21:24:39.218183596+00:00"},"epss":{"cve":"CVE-2021-41136","score":0.01203,"percentile":0.68257,"date":"2026-10-31"},"kev":null,"osv":[{"id":"GHSA-48w2-rm65-62xx","url":"https://osv.dev/vulnerability/GHSA-48w2-rm65-62xx","summary":"Puma with proxy which forwards LF characters as line endings could allow HTTP request smuggling","modified":"2026-07-08T06:28:18.680516550Z","packages":[{"ecosystem":"RubyGems","name":"puma","purl":"pkg:gem/puma","ranges":[">=5.0.0 <5.5.1"],"fixed":["5.5.1"]},{"ecosystem":"RubyGems","name":"puma","purl":"pkg:gem/puma","ranges":["<4.3.9"],"fixed":["4.3.9"]}]}],"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."]}