CVE-2021-29509: Keepalive Connections Causing Denial Of Service in puma
First published: Tue May 11 2021(Updated: )
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.
Credit: security-advisories@github.com
| Affected Software | Affected Version | How to fix |
|---|---|---|
| Puma Puma | <4.3.8 | |
| Puma Puma | >=5.0.0<5.3.1 | |
| Debian Debian Linux | =10.0 |
Never miss a vulnerability like this again
Sign up to SecAlerts for real-time vulnerability data matched to your software, aggregated from hundreds of sources.
Reference Links
- https://gist.github.com/nateberkopec/4b3ea5676c0d70cbb37c82d54be25837
- https://github.com/puma/puma/security/advisories/GHSA-q28m-8xjw-8vr5
- https://github.com/puma/puma/security/policy
- https://lists.debian.org/debian-lts-announce/2022/08/msg00015.html
- https://rubygems.org/gems/puma
- https://security.gentoo.org/glsa/202208-28
- https://access.redhat.com/security/cve/CVE-2019-16770
- https://bugzilla.redhat.com/show_bug.cgi/show_bug.cgi?id=1964875
- https://github.com/puma/puma/issues/2625
- https://github.com/puma/puma/commit/df72887170c7ef3614c941c9bdefb4a1f3546ebf
- https://access.redhat.com/errata/RHSA-2021:4702
- https://bugzilla.redhat.com/show_bug.cgi?id=1964874
Frequently Asked Questions
What is CVE-2021-29509?
CVE-2021-29509 is a vulnerability in the Puma HTTP server that allows greedy persistent connections to saturate all threads in the same process, resulting in denial-of-service (DoS) conditions.
What is the severity of CVE-2021-29509?
The severity of CVE-2021-29509 is high, with a CVSS score of 7.5.
How does CVE-2021-29509 affect Puma?
CVE-2021-29509 affects Puma versions up to and excluding 4.3.8 and versions up to and excluding 5.3.1.
How can I fix CVE-2021-29509?
To fix CVE-2021-29509, update your Puma installation to version 4.3.8 or higher for versions below 5.0.0, or version 5.3.1 or higher for versions between 5.0.0 and 5.3.1.
Where can I find more information about CVE-2021-29509?
You can find more information about CVE-2021-29509 on the Red Hat Security Advisory page: https://access.redhat.com/security/cve/CVE-2019-16770
- collector/nvd-index
- agent/weakness
- agent/type
- agent/remedy
- agent/softwarecombine
- agent/references
- agent/author
- agent/description
- collector/redhat-bugzilla
- source/Red Hat
- alias/CVE-2021-29509
- agent/software-canonical-lookup
- collector/mitre-cve
- source/MITRE
- agent/last-modified-date
- agent/title
- agent/severity
- agent/tags
- agent/first-publish-date
- agent/event
- vendor/puma
- canonical/puma puma
- version/puma puma/5.0.0
- vendor/debian
- canonical/debian debian linux
- version/debian debian linux/10.0
- package-manager/redhat