A poorly-behaved client could use keepalive requests to monopolize Puma's reactor and create a denial of service attack

Exploitation

No confirmed exploitation recorded. Patch Next marks exploitation only from CISA KEV.

CVSS

5.3 · CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:L

EPSS

• CVE-2019-16770: 2.01% estimated exploitation activity in the next 30 days; percentile 80.92 (FIRST EPSS, 2026-11-03). This is a model estimate, not proof of exploitation or customer exposure.

As published by the source; long descriptions are shortened.

Keepalive thread overload/DoS Impact A poorly-behaved client could use keepalive requests to monopolize Puma's reactor and create a denial of service attack. If more keepalive connections to Puma are opened than there are threads available, additional connections will wait permanently if the attacker sends requests frequently enough. Patches This vulnerability is patched in Puma 4.3.1 and 3.12.2. Workarounds Reverse proxies in front of Puma could be configured to always allow less than X keepalive connections to a Puma cluster or process, where X is the number of threads configured in Puma's thread pool. For more information If you have any questions or comments about this advisory: Open an issue at puma.

Published by the source

5 Dec 2019, 19:26 UTC

Last modified by the source

4 May 2023, 19:53 UTC

Source last checked

26 Oct 2026, 15:47 UTC

1. Revision 1 · created · 26 Oct 2026

   Published from ghsa record GHSA-7xx3-m584-x994

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# Patch Next advisory brief: CVE-2019-16770

Advisory: A poorly-behaved client could use keepalive requests to monopolize Puma's reactor and create a denial of service attack
IDs: CVE-2019-16770, GHSA-7xx3-m584-x994
Record: https://patchnext.com/advisories/cve-2019-16770 (revision 1, source checked 26 Oct 2026, 15:47 UTC)
Inventory: none attached. This brief comes from a public page and does not say whether any deployment is affected.
Severity: Medium (CVSS 5.3)
Exploitation: no confirmed exploitation recorded. Patch Next confirms exploitation only from CISA KEV.
Vendor response: Vendor fix available; fixed versions by package: puma 4.3.1, 3.12.2. A vendor fix does not mean a deployment is fixed.

## Affected components
- RubyGems puma: affected < 3.12.2; >= 4.0.0, < 4.3.1; fixed in 4.3.1, 3.12.2

## Suggested inspection (read-only)
- RubyGems puma: check the installed version with your package manager.

## Supported action
Upgrade each affected component to a fixed version on its release line. For a transitive dependency, upgrade the parent package or add an override or constraint, then regenerate the lockfile. Redeploy every environment that ran an affected version.

## Required regression checks
- Run the test suite and a production build.
- Exercise the features that depend on puma.
- Repeat the inspection and confirm that only fixed versions remain installed.

## Rollback considerations
- Keep the previous lockfile and deployment artifact. Rolling back reinstates the vulnerable version, so apply any documented mitigation while you fix forward.

## Unresolved questions
- Which deployments run an affected version?
- Exploitation status can change. Check again before lowering the priority.
- Mark the work resolved only after the fixed version is verified in production.

## Sources
- Verified: https://github.com/advisories/GHSA-7xx3-m584-x994 (GitHub-reviewed advisory GHSA-7xx3-m584-x994 lists affected ranges: RubyGems puma >=0 =4.0.0 <4.3.1)

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