ubuntu-cve-2021-29509
Vulnerability from osv_ubuntu
Published
2021-05-11 17:15
Modified
2025-07-16 04:57
Summary
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.

Severity
7.5 (High)
CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:H
7.5 (High)
CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:H
N/A (UNKNOWN)
medium
References
To clipboard 

{
  "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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