{"id":"CVE-2026-47736","aliases":["GHSA-qpgp-93vx-g8v8"],"url":"https://o3.security/vulnerability/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)","published":"2026-07-14T19:54:26.229Z","modified":"2026-08-12T03:51:44.405328802Z","cvss":{"score":7.5,"severity":"HIGH","vector":"CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:H"},"epss":{"score":0.0063,"percentile":0.47443,"asOf":"2026-08-24"},"cisaKev":null,"exploitsKnown":0,"affectedPackages":[{"ecosystem":"RubyGems","name":"puma","fixedVersion":"8.0.2"},{"ecosystem":"RubyGems","name":"puma","fixedVersion":"7.2.1"}],"fix":{"url":"https://github.com/puma/puma/commit/439c6136d9c2275721b7864db3ee78af7c80889f","label":"puma/puma@439c613"},"references":[{"type":"WEB","url":"https://github.com/puma/puma/releases/tag/v7.2.1"},{"type":"WEB","url":"https://github.com/puma/puma/releases/tag/v8.0.2"},{"type":"ADVISORY","url":"https://github.com/CVEProject/cvelistV5/tree/main/cves/2026/47xxx/CVE-2026-47736.json"},{"type":"ADVISORY","url":"https://github.com/puma/puma/security/advisories/GHSA-qpgp-93vx-g8v8"},{"type":"ADVISORY","url":"https://nvd.nist.gov/vuln/detail/CVE-2026-47736"},{"type":"FIX","url":"https://github.com/puma/puma/commit/439c6136d9c2275721b7864db3ee78af7c80889f"},{"type":"FIX","url":"https://github.com/puma/puma/commit/ebe9db3929ab8299d19c8f5b41e8ef4f4b22fa58"},{"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"}],"provenance":{"sources":["OSV.dev","FIRST.org (EPSS)"],"lastVerified":"2026-08-12T03:51:44.405328802Z"}}