https://cve.radiocsirt.org/rss/recent/all/10 Most recent entries from all 2026-10-07T11:23:48.253557+00:00 Vulnerability-Lookup csirt@opendfir.org python-feedgen Contains only the most 10 recent entries. https://cve.radiocsirt.org/vuln/cve-2021-29509 CVE-2021-29509 — Keepalive Connections Causing Denial Of Service in puma 2026-10-07T11:23:48.272657+00:00

Affected: puma

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.

 https://cve.radiocsirt.org/vuln/ghsa-q28m-8xjw-8vr5 GHSA-q28m-8xjw-8vr5 — Puma's Keepalive Connections Causing Denial Of Service 2026-10-07T11:23:48.272728+00:00

Affected: RubyGems: puma

This vulnerability is related to [CVE-2019-16770](https://github.com/puma/puma/security/advisories/GHSA-7xx3-m584-x994).

### Impact

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.

### Patches

This problem has been fixed in `puma` 4.3.8 and 5.3.1.

### Workarounds

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](https://en.wikipedia.org/wiki/Slowloris_(computer_security))).

The fix is very small. [A git patch is available here](https://gist.github.com/nateberkopec/4b3ea5676c0d70cbb37c82d54be25837) for those using [unsupported versions](https://github.com/puma/puma/security/policy#supported-versions) of Puma.

### For more information

If you have any questions or comments about this advisory:

* Open an issue in [Puma](https://github.com/puma/puma). * To report problems with this f…