GHSA-q28m-8xjw-8vr5
HIGHGHSA-q28m-8xjw-8vr5 is a high-severity (CVSS 7.5) Uncontrolled Resource Consumption vulnerability in puma. O3 Security confirms whether GHSA-q28m-8xjw-8vr5 is actually reachable in your code before you act, and blocks exploitation at runtime until you patch.
Puma's Keepalive Connections Causing Denial Of Service
Blast Radius
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Description
This vulnerability is related to CVE-2019-16770.
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).
The fix is very small. A git patch is available here for those using unsupported versions of Puma.
For more information
If you have any questions or comments about this advisory:
- Open an issue in Puma.
- To report problems with this fix or to report another vulnerability, see our security policy.
Acknowledgements
Thank you to @MSP-Greg, @wjordan and @evanphx for their review on this issue.
Thank you to @ioquatix for providing a modified fork of wrk which made debugging this issue much easier.
Affected Packages
| Ecosystem | Package | Vulnerable range | Fix |
|---|---|---|---|
| 💎RubyGems | puma | all versions | 4.3.8 |
| 💎RubyGems | puma | ≥ 5.0.0&&< 5.3.1 | 5.3.1 |
Detection & mitigation playbook
Open-source dependencyDetect
Scan your dependency tree (package-lock.json, pnpm-lock.yaml, requirements.txt, go.sum, etc.) for puma. O3's reachability analysis confirms whether the vulnerable code path is actually invoked in your application, so you act on real exposure instead of every transitive match.
Fix
Update puma to 4.3.8 or later, then make sure no transitive (indirect) dependency still pins the vulnerable range — O3 confirms GHSA-q28m-8xjw-8vr5 is resolved across your whole dependency graph.
Workarounds
If you can't upgrade right away: gate or disable the affected feature, validate untrusted input at the boundary, and avoid passing attacker-controlled data into the vulnerable path. O3's runtime protection blocks exploitation in production as an interim safeguard until the upgrade lands.
How O3 protects you
O3 pinpoints whether GHSA-q28m-8xjw-8vr5 is reachable in your code and exactly where to fix it, then blocks exploitation in production at runtime until the patched version is deployed.
Tailored to GHSA-q28m-8xjw-8vr5. Runtime protection reduces exposure until a permanent patch is applied and verified — it complements patching, it doesn't replace it.
Frequently Asked Questions
Is GHSA-q28m-8xjw-8vr5 in your dependencies?
O3 detects GHSA-q28m-8xjw-8vr5 across RubyGems dependencies and uses function-level reachability to confirm whether the vulnerable code path is actually reachable — not just present. No false positives.