CVE-2026-47736: Puma Puma PROXY Protocol V1 Parser Vulnerability

{
  "schema_version" : "1.4.0",
  "id" : "GHSA-qpgp-93vx-g8v8",
  "modified" : "2026-06-08T23:55:44Z",
  "published" : "2026-06-08T23:55:44Z",
  "aliases" : [ "CVE-2026-47736" ],
  "summary" : "Puma PROXY Protocol v1 Parser Allows Remote Memory Exhaustion ",
  "details" : "### Impact\n\n[PROXY protocol support for Puma](https://github.com/puma/puma/issues/2651) was added in version 5.5.0.\n\nWhen 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.\n\nThis 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.\n\n**Only Puma servers using the following non-default config are affected:**\n\n```ruby\n   set_remote_address proxy_protocol: :v1\n```\n\n### Patches\n\nUsers should upgrade to versions 7.2.1 or 8.0.2.\n\n### Workarounds\n\n- Disable PROXY protocol v1 parsing if it is not required:\n\n ```ruby\n   # remove/comment this:\n   # set_remote_address proxy_protocol: :v1\n ```\n\n - Restrict direct network access to Puma listeners using PROXY protocol:\n     - Only allow trusted load balancers/reverse proxies to connect.\n     - Block arbitrary client TCP access with firewall/security group rules.\n\n### Resources\n- [HAProxy PROXY protocol specification](https://www.haproxy.org/download/1.8/doc/proxy-protocol.txt)\n- [CWE-400: Uncontrolled Resource Consumption](https://cwe.mitre.org/data/definitions/400.html)\n- [CWE-770: Allocation of Resources Without Limits or Throttling](https://cwe.mitre.org/data/definitions/770.html)\n- [Puma `set_remote_address` documentation](https://github.com/puma/puma/blob/master/lib/puma/dsl.rb)\n- [Puma client PROXY protocol parsing code](https://github.com/puma/puma/blob/master/lib/puma/client.rb)\n- [Puma constants, including `PROXY_PROTOCOL_V1_REGEX`](https://github.com/puma/puma/blob/master/lib/puma/const.rb)",
  "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" : "8.0.0"
      }, {
        "fixed" : "8.0.2"
      } ]
    } ]
  }, {
    "package" : {
      "ecosystem" : "RubyGems",
      "name" : "puma"
    },
    "ranges" : [ {
      "type" : "ECOSYSTEM",
      "events" : [ {
        "introduced" : "5.5.0"
      }, {
        "fixed" : "7.2.1"
      } ]
    } ]
  } ],
  "references" : [ {
    "type" : "WEB",
    "url" : "https://github.com/puma/puma/security/advisories/GHSA-qpgp-93vx-g8v8"
  }, {
    "type" : "PACKAGE",
    "url" : "https://github.com/puma/puma"
  }, {
    "type" : "WEB",
    "url" : "https://github.com/rubysec/ruby-advisory-db/blob/master/gems/puma/CVE-2026-47736.yml"
  }, {
    "type" : "WEB",
    "url" : "https://www.cve.org/CVERecord?id=CVE-2026-47736"
  } ],
  "database_specific" : {
    "cwe_ids" : [ "CWE-400" ],
    "severity" : "HIGH",
    "github_reviewed" : true,
    "github_reviewed_at" : "2026-06-08T23:55:44Z",
    "nvd_published_at" : null
  }
}