CVE-2021-29509

Date: May 11, 2021

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.

Language: Ruby