CVE-2021-29509
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.
Predictions
Heuristic predictions, AS-IS, for prioritization only.
Mitigations
No mitigations published for this CVE yet.
The vendor-content worker queues fetches as references arrive (check back in a few minutes). Or — if you've already worked around this in production — publish your fix to the community-verified tier.
✚ Propose a mitigation on Community → Mitigations published via the community go through AI scoring + 2 human reviewers + 7-day silent objection window before landing here withsource_tier=community-verified.
OS impact
| OS | Version | Status | Fixed in |
|---|---|---|---|
| sles | affected | | |
| debian | bookworm | fixed | 4.3.8-1 |
| debian | bullseye | fixed | 4.3.8-1 |
| debian | forky | fixed | 4.3.8-1 |
| debian | sid | fixed | 4.3.8-1 |
| debian | trixie | fixed | 4.3.8-1 |
References
- https://github.com/puma/puma/security/advisories/GHSA-q28m-8xjw-8vr5
- https://www.suse.com/security/cve/CVE-2021-29509.html
- https://nvd.nist.gov/vuln/detail/CVE-2021-29509
- https://gist.github.com/nateberkopec/4b3ea5676c0d70cbb37c82d54be25837
- https://github.com/puma/puma
- https://github.com/puma/puma/security/policy
- https://github.com/rubysec/ruby-advisory-db/blob/master/gems/puma/CVE-2021-29509.yml
- https://lists.debian.org/debian-lts-announce/2022/08/msg00015.html
- https://rubygems.org/gems/puma
- https://security.gentoo.org/glsa/202208-28
- https://security-tracker.debian.org/tracker/CVE-2021-29509
Community-verified mitigations for this CVE will appear above when contributors publish them.
Verify integrity in audit chain (admin only). AS-IS.