CVE-2021-29509: Puma Denial of Service Vulnerability

{
  "schema_version" : "1.4.0",
  "id" : "GHSA-q28m-8xjw-8vr5",
  "modified" : "2023-05-16T16:19:44Z",
  "published" : "2021-05-18T01:27:15Z",
  "aliases" : [ "CVE-2021-29509" ],
  "summary" : "Puma's Keepalive Connections Causing Denial Of Service",
  "details" : "This vulnerability is related to [CVE-2019-16770](https://github.com/puma/puma/security/advisories/GHSA-7xx3-m584-x994).\n\n### Impact\n\nThe 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.\n\nA `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.\n\n### Patches\n\nThis problem has been fixed in `puma` 4.3.8 and 5.3.1.\n\n### Workarounds\n\nSetting `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](https://en.wikipedia.org/wiki/Slowloris_(computer_security))).\n\nThe fix is very small. [A git patch is available here](https://gist.github.com/nateberkopec/4b3ea5676c0d70cbb37c82d54be25837) for those using [unsupported versions](https://github.com/puma/puma/security/policy#supported-versions) of Puma.\n\n### For more information\n\nIf you have any questions or comments about this advisory:\n\n* Open an issue in [Puma](https://github.com/puma/puma).\n* To report problems with this fix or to report another vulnerability, see [our security policy.](https://github.com/puma/puma/security/policy)\n\n### Acknowledgements\n\nThank you to @MSP-Greg, @wjordan and @evanphx for their review on this issue. \n\nThank you to @ioquatix for providing a modified fork of `wrk` which made debugging this issue much easier.",
  "severity" : [ {
    "type" : "CVSS_V3",
    "score" : "CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:H"
  } ],
  "affected" : [ {
    "package" : {
      "ecosystem" : "RubyGems",
      "name" : "puma"
    },
    "ranges" : [ {
      "type" : "ECOSYSTEM",
      "events" : [ {
        "introduced" : "0"
      }, {
        "fixed" : "4.3.8"
      } ]
    } ],
    "database_specific" : {
      "last_known_affected_version_range" : "<= 4.3.7"
    }
  }, {
    "package" : {
      "ecosystem" : "RubyGems",
      "name" : "puma"
    },
    "ranges" : [ {
      "type" : "ECOSYSTEM",
      "events" : [ {
        "introduced" : "5.0.0"
      }, {
        "fixed" : "5.3.1"
      } ]
    } ],
    "database_specific" : {
      "last_known_affected_version_range" : "<= 5.3.0"
    }
  } ],
  "references" : [ {
    "type" : "WEB",
    "url" : "https://github.com/puma/puma/security/advisories/GHSA-q28m-8xjw-8vr5"
  }, {
    "type" : "ADVISORY",
    "url" : "https://nvd.nist.gov/vuln/detail/CVE-2021-29509"
  }, {
    "type" : "WEB",
    "url" : "https://gist.github.com/nateberkopec/4b3ea5676c0d70cbb37c82d54be25837"
  }, {
    "type" : "PACKAGE",
    "url" : "https://github.com/puma/puma"
  }, {
    "type" : "WEB",
    "url" : "https://github.com/puma/puma/security/policy"
  }, {
    "type" : "WEB",
    "url" : "https://github.com/rubysec/ruby-advisory-db/blob/master/gems/puma/CVE-2021-29509.yml"
  }, {
    "type" : "WEB",
    "url" : "https://lists.debian.org/debian-lts-announce/2022/08/msg00015.html"
  }, {
    "type" : "WEB",
    "url" : "https://rubygems.org/gems/puma"
  }, {
    "type" : "WEB",
    "url" : "https://security.gentoo.org/glsa/202208-28"
  } ],
  "database_specific" : {
    "cwe_ids" : [ "CWE-400" ],
    "severity" : "HIGH",
    "github_reviewed" : true,
    "github_reviewed_at" : "2021-05-18T01:26:55Z",
    "nvd_published_at" : "2021-05-11T17:15:00Z"
  }
}