CVE-2021-29509

NameCVE-2021-29509
DescriptionPuma 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.
SourceCVE (at NVD; CERT, LWN, oss-sec, fulldisc, bugtraq, EDB, Metasploit, Red Hat, Ubuntu, Gentoo, SUSE bugzilla/CVE, Mageia, GitHub code/issues, web search, more)
NVD severitymedium
Debian Bugs989054

Vulnerable and fixed packages

The table below lists information on source packages.

Source PackageReleaseVersionStatus
puma (PTS)stretch3.6.0-1fixed
stretch (security)3.6.0-1+deb9u1fixed
buster3.12.0-2+deb10u2vulnerable
bullseye, sid4.3.8-1fixed

The information below is based on the following data on fixed versions.

PackageTypeReleaseFixed VersionUrgencyOriginDebian Bugs
pumasourcestretch(not affected)
pumasource(unstable)4.3.8-1989054

Notes

[stretch] - puma <not-affected> (Incomplete fix for CVE-2019-16770 not applied)
https://github.com/puma/puma/security/advisories/GHSA-q28m-8xjw-8vr5
https://github.com/puma/puma/commit/df72887170c7ef3614c941c9bdefb4a1f3546ebf
CVE is related to an incomplete fix for CVE-2019-16770

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