ruby-advisory-db/gems/puma/CVE-2026-47736.yml at master · rubysec/ruby-advisory-db · GitHub

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---
gem: puma
cve: 2026-47736
ghsa: qpgp-93vx-g8v8
url: https://www.cve.org/CVERecord?id=CVE-2026-47736
title: Puma PROXY Protocol v1 Parser Allows Remote Memory Exhaustion
date: 2026-05-27
description: |
  ## Impact

  PROXY protocol support for Puma was added in version 5.5.0.

  When PROXY protocol v1 support is enabled, Puma reads incoming bytes
  into an internal buffer. It waits for "\r\n" to determine whether a
  PROXY v1 line is present. If an attacker opens a TCP connection and
  continuously sends bytes without CRLF, Puma keeps appending to this
  pre-parse buffer.

  This can cause unbounded in-process memory growth and additional
  CPU cost from repeatedly scanning the growing buffer for CRLF.
  A single, unauthenticated TCP connection can drive significant memory
  growth and may cause process/container OOM or degraded availability.

   Only Puma servers using the following non-default config are affected:

   set_remote_address proxy_protocol: :v1

  ## Workarounds

  * Disable PROXY protocol v1 parsing if it is not required:
    # remove/comment this:
    # set_remote_address proxy_protocol: :v1

  * Restrict direct network access to Puma listeners using PROXY protocol:
    * Only allow trusted load balancers/reverse proxies to connect.
    * Block arbitrary client TCP access with firewall/security group rules.
cvss_v3: 7.5
unaffected_versions:
  - "< 5.5.0"
patched_versions:
  - "~> 7.2.1"
  - ">= 8.0.2"
related:
  url:
    - https://www.cve.org/CVERecord?id=CVE-2026-47736
    - https://rubygems.org/gems/puma/versions/8.0.2
    - https://github.com/puma/puma/releases/tag/v8.0.2
    - https://github.com/puma/puma/releases/tag/v7.2.1
    - https://github.com/puma/puma/blob/main/History.md#802--2026-05-27
    - https://github.com/puma/puma/blob/main/History.md#721--2026-05-27
    - https://github.com/puma/puma/pull/2654
    - https://github.com/puma/puma/issues/2651
    - https://rubyweekly.com/issues/803
    - https://advisories.gitlab.com/gem/puma/CVE-2026-47736
    - https://github.com/puma/puma/security/advisories/GHSA-qpgp-93vx-g8v8
notes: |
  - https://www.cve.org/CVERecord/SearchResults?query=CVE-2026-47736 (reserved)
  - No nvd cvss values