{"id":"UBUNTU-CVE-2021-29509","details":"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those using unsupported versions of Puma.","modified":"2025-07-16T07:34:22.664900Z","published":"2021-05-11T17:15:00Z","withdrawn":"2025-07-18T16:46:45Z","upstream":["CVE-2021-29509"],"references":[{"type":"REPORT","url":"https://ubuntu.com/security/CVE-2021-29509"},{"type":"REPORT","url":"https://rubygems.org/gems/puma"},{"type":"REPORT","url":"https://github.com/puma/puma/security/policy"},{"type":"REPORT","url":"https://github.com/puma/puma/security/advisories/GHSA-q28m-8xjw-8vr5"},{"type":"REPORT","url":"https://www.cve.org/CVERecord?id=CVE-2021-29509"}],"affected":[{"package":{"name":"puma","ecosystem":"Ubuntu:20.04:LTS","purl":"pkg:deb/ubuntu/puma@3.12.4-1ubuntu2?arch=source&distro=focal"},"ranges":[{"type":"ECOSYSTEM","events":[{"introduced":"0"},{"fixed":"3.12.4-1ubuntu2"}]}],"versions":["3.12.0-2ubuntu1","3.12.0-4ubuntu1"],"ecosystem_specific":{"availability":"No subscription required","binaries":[{"binary_name":"puma","binary_version":"3.12.4-1ubuntu2"},{"binary_name":"puma-dbgsym","binary_version":"3.12.4-1ubuntu2"}]},"database_specific":{"source":"https://github.com/canonical/ubuntu-security-notices/blob/main/osv/cve/2021/UBUNTU-CVE-2021-29509.json"}},{"package":{"name":"puma","ecosystem":"Ubuntu:22.04:LTS","purl":"pkg:deb/ubuntu/puma@5.5.2-2ubuntu2?arch=source&distro=jammy"},"ranges":[{"type":"ECOSYSTEM","events":[{"introduced":"0"},{"fixed":"5.5.2-2ubuntu2"}]}],"versions":["4.3.6-1ubuntu4"],"ecosystem_specific":{"availability":"No subscription required","binaries":[{"binary_name":"puma","binary_version":"5.5.2-2ubuntu2"},{"binary_version":"5.5.2-2ubuntu2","binary_name":"puma-dbgsym"}]},"database_specific":{"source":"https://github.com/canonical/ubuntu-security-notices/blob/main/osv/cve/2021/UBUNTU-CVE-2021-29509.json"}}],"schema_version":"1.7.3","severity":[{"type":"CVSS_V3","score":"CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:H"},{"type":"CVSS_V3","score":"CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:H"},{"type":"Ubuntu","score":"medium"}]}