UBUNTU-CVE-2021-29509 (CVE-2021-29509)
Vulnerability from osv_ubuntu – Published: 2021-05-11 17:15 – Updated: 2025-07-16 04:57 – Source websitePuma 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.
{
"affected": [
{
"ecosystem_specific": {
"availability": "No subscription required",
"binaries": [
{
"binary_name": "puma",
"binary_version": "3.12.4-1ubuntu2"
},
{
"binary_name": "puma-dbgsym",
"binary_version": "3.12.4-1ubuntu2"
}
]
},
"package": {
"ecosystem": "Ubuntu:20.04:LTS",
"name": "puma",
"purl": "pkg:deb/ubuntu/puma@3.12.4-1ubuntu2?arch=source\u0026distro=focal"
},
"ranges": [
{
"events": [
{
"introduced": "0"
},
{
"fixed": "3.12.4-1ubuntu2"
}
],
"type": "ECOSYSTEM"
}
],
"versions": [
"3.12.0-2ubuntu1",
"3.12.0-4ubuntu1"
]
},
{
"ecosystem_specific": {
"availability": "No subscription required",
"binaries": [
{
"binary_name": "puma",
"binary_version": "5.5.2-2ubuntu2"
},
{
"binary_name": "puma-dbgsym",
"binary_version": "5.5.2-2ubuntu2"
}
]
},
"package": {
"ecosystem": "Ubuntu:22.04:LTS",
"name": "puma",
"purl": "pkg:deb/ubuntu/puma@5.5.2-2ubuntu2?arch=source\u0026distro=jammy"
},
"ranges": [
{
"events": [
{
"introduced": "0"
},
{
"fixed": "5.5.2-2ubuntu2"
}
],
"type": "ECOSYSTEM"
}
],
"versions": [
"4.3.6-1ubuntu4"
]
}
],
"aliases": [],
"details": "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.",
"id": "UBUNTU-CVE-2021-29509",
"modified": "2025-07-16T04:57:11Z",
"published": "2021-05-11T17:15:00Z",
"references": [
{
"type": "REPORT",
"url": "https://ubuntu.com/security/CVE-2021-29509"
},
{
"type": "REPORT",
"url": "https://rubygems.org/gems/puma"
},
{
"type": "REPORT",
"url": "https://github.com/puma/puma/security/policy"
},
{
"type": "REPORT",
"url": "https://github.com/puma/puma/security/advisories/GHSA-q28m-8xjw-8vr5"
},
{
"type": "REPORT",
"url": "https://www.cve.org/CVERecord?id=CVE-2021-29509"
}
],
"related": [],
"schema_version": "1.7.0",
"severity": [
{
"score": "CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:H",
"type": "CVSS_V3"
},
{
"score": "CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:H",
"type": "CVSS_V3"
},
{
"score": "medium",
"type": "Ubuntu"
}
],
"upstream": [
"CVE-2021-29509"
],
"withdrawn": "2025-07-18T16:46:45Z"
}
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