CVE-2026-47073: Hackney Hackney Has Unbounded Buffer Accumulation Vulnerability

{
  "schema_version" : "1.4.0",
  "id" : "GHSA-q8jg-fgj4-fphf",
  "modified" : "2026-06-26T22:00:16Z",
  "published" : "2026-06-26T22:00:16Z",
  "aliases" : [ "CVE-2026-47073" ],
  "summary" : "Hackney has unbounded buffer accumulation in WebSocket",
  "details" : "### Summary\n\nThe WebSocket client in `src/hackney_ws.erl` imposes no upper bound on memory consumption across three distinct code paths. In each case, an attacker-controlled WebSocket server can exhaust the connecting process's memory without any authentication or special client configuration.\n\n### Details\n\n**1. Handshake response buffer (`read_handshake_response/3`)**\n\nThe function accumulates received bytes into a growing buffer waiting for `\\r\\n\\r\\n`. The per-receive timeout resets on every chunk, so a server that trickles bytes indefinitely without completing the HTTP upgrade response grows the buffer until OOM. No total-size cap exists.\n\n**2. Frame payload accumulation (`parse_payload/9`, `parse_active_payload/8`)**\n\n`parse_payload/9` (lines 816–817 and 825–826) appends each received chunk into a `Buffer` binary via `<<Buffer/binary, MoreData/binary>>` whenever the frame parser returns `{more, ...}`. `parse_active_payload/8` does the same in active mode by appending each incoming `tcp`/`ssl` message to `#ws_data.buffer`. RFC 6455 permits payload lengths up to 2⁶³-1 bytes, and neither path validates the declared `Len` against any limit. The `recv_timeout` applies per chunk, not to the whole frame, so a slow trickle never triggers it.\n\n**3. Fragmentation buffer (`frag_buffer`)**\n\nThe `frag_buffer` field of `#ws_data{}` accumulates continuation frames. A server that sends an unbounded stream of non-final (`nofin`) fragments without ever sending a final (`fin`) frame grows `frag_buffer` without bound.\n\n### PoC\n\n1. Stand up a WebSocket server and connect to it with hackney's WebSocket client.\n2. Trigger any of the three paths: (a) never send `\\r\\n\\r\\n` during the handshake; (b) announce a very large frame payload and dribble bytes slowly; (c) send an endless stream of `nofin` continuation frames.\n3. Observe the hackney process's memory growing until the BEAM OOM-kills it or the node crashes.\n\n### Impact\n\nDenial of service via unbounded memory consumption. Affects hackney 2.0.0 through 4.0.0 for any application using the WebSocket client against an attacker-controlled server. No authentication or special configuration is required on the client side. CVSS v4.0: **8.7 (HIGH)**.\n\n## Resources\n\n* Introduction commit: https://github.com/benoitc/hackney/commit/690cecaf236fba49526da404a5bc889a24367a3e\n* Patch commit: https://github.com/benoitc/hackney/commit/ce0109e2970ace6e20ff29bae9d05c3ac22ec6dc",
  "severity" : [ {
    "type" : "CVSS_V4",
    "score" : "CVSS:4.0/AV:N/AC:L/AT:N/PR:N/UI:N/VC:N/VI:N/VA:H/SC:N/SI:N/SA:N"
  } ],
  "affected" : [ {
    "package" : {
      "ecosystem" : "Hex",
      "name" : "hackney"
    },
    "ranges" : [ {
      "type" : "ECOSYSTEM",
      "events" : [ {
        "introduced" : "2.0.0"
      }, {
        "fixed" : "4.0.1"
      } ]
    } ]
  } ],
  "references" : [ {
    "type" : "WEB",
    "url" : "https://github.com/benoitc/hackney/security/advisories/GHSA-q8jg-fgj4-fphf"
  }, {
    "type" : "ADVISORY",
    "url" : "https://nvd.nist.gov/vuln/detail/CVE-2026-47073"
  }, {
    "type" : "WEB",
    "url" : "https://github.com/benoitc/hackney/commit/ce0109e2970ace6e20ff29bae9d05c3ac22ec6dc"
  }, {
    "type" : "WEB",
    "url" : "https://cna.erlef.org/cves/CVE-2026-47073.html"
  }, {
    "type" : "PACKAGE",
    "url" : "https://github.com/benoitc/hackney"
  }, {
    "type" : "WEB",
    "url" : "https://osv.dev/vulnerability/EEF-CVE-2026-47073"
  } ],
  "database_specific" : {
    "cwe_ids" : [ "CWE-400" ],
    "severity" : "HIGH",
    "github_reviewed" : true,
    "github_reviewed_at" : "2026-06-26T22:00:16Z",
    "nvd_published_at" : "2026-05-25T15:16:22Z"
  }
}