{"id":"CVE-2021-29509","state":"PUBLISHED","title":"Keepalive Connections Causing Denial Of Service in puma","description":"Puma is a concurrent HTTP 1.1 server for Ruby/Rack applications. The fix for CVE-2019-16770 was incomplete. The original fix only protected existing connections that had already been accepted from having their requests starved by greedy persistent-connections saturating all threads in the same process. However, new connections may still be starved by greedy persistent-connections saturating all threads in all processes in the cluster. A `puma` server which received more concurrent `keep-alive` connections than the server had threads in its threadpool would service only a subset of connections, denying service to the unserved connections. This problem has been fixed in `puma` 4.3.8 and 5.3.1. Setting `queue_requests false` also fixes the issue. This is not advised when using `puma` without a reverse proxy, such as `nginx` or `apache`, because you will open yourself to slow client attacks (e.g. slowloris). The fix is very small and a git patch is available for those using unsupported versions of Puma.","publishedAt":"2021-05-11T16:50:11.000Z","updatedAt":"2024-08-03T22:11:05.438Z","severity":{"score":7.5,"label":"High","version":"3.1","vector":"CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:H","source":"GitHub_M"},"assigner":"GitHub_M","products":["puma puma"],"affected":[{"vendor":"puma","product":"puma","versions":[{"version":"< 4.3.8","status":"affected"},{"version":">= 5.0.0, < 5.3.1","status":"affected"}]}],"references":["https://github.com/puma/puma/security/advisories/GHSA-q28m-8xjw-8vr5","https://gist.github.com/nateberkopec/4b3ea5676c0d70cbb37c82d54be25837","https://github.com/puma/puma/security/policy","https://rubygems.org/gems/puma","https://security.gentoo.org/glsa/202208-28","https://lists.debian.org/debian-lts-announce/2022/08/msg00015.html"],"weaknesses":["CWE-400"],"ingestedAt":"2026-10-29T19:48:21.578Z","source":{"repository":"CVEProject/cvelistV5","path":"cves/2021/29xxx/CVE-2021-29509.json","commit":"556c9d3a8cd17e218bb8e452ba7cd619a384ff47"},"raw":{"dataType":"CVE_RECORD","dataVersion":"5.1","cveMetadata":{"cveId":"CVE-2021-29509","state":"PUBLISHED","datePublished":"2021-05-11T16:50:11.000Z","dateUpdated":"2024-08-03T22:11:05.438Z","assignerShortName":"GitHub_M","assignerOrgId":"a0819718-46f1-4df5-94e2-005712e83aaa","dateReserved":"2021-03-30T00:00:00.000Z"},"containers":{"cna":{"title":"Keepalive Connections Causing Denial Of Service in puma","descriptions":[{"lang":"en","value":"Puma is a concurrent HTTP 1.1 server for Ruby/Rack applications. 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