CVE-2021-29509 Keepalive Connections Causing Denial Of Service in puma

2021-05-1116:50:11

CWE-400

GitHub_M

www.cve.org

7.5 High

CVSS3

Attack Vector

NETWORK

Attack Complexity

LOW

Privileges Required

NONE

User Interaction

NONE

Scope

UNCHANGED

Confidentiality Impact

NONE

Integrity Impact

NONE

Availability Impact

HIGH

CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:H

7.6 High

AI Score

Confidence

High

0.02 Low

EPSS

Percentile

88.8%

JSON

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.

CNA Affected

[
  {
    "product": "puma",
    "vendor": "puma",
    "versions": [
      {
        "status": "affected",
        "version": "< 4.3.8"
      },
      {
        "status": "affected",
        "version": ">= 5.0.0, < 5.3.1"
      }
    ]
  }
]