Unbounded buffer accumulation in multipart header parsing causes denial of service in cowboy

{
  "id": "83fcb08c10162a6aea69a1b7c2c3eff5ae1b67179067fc04775ae923c15e2b0b",
  "url": "https://osv.dev/vulnerability/CVE-2026-8466",
  "method": "structured",
  "payload": {
    "kind": "advisory",
    "title": "Unbounded buffer accumulation in multipart header parsing causes denial of service in cowboy",
    "summary": "Allocation of Resources Without Limits or Throttling vulnerability in ninenines cowboy allows denial of service via unbounded buffer accumulation in multipart header parsing. cowboy_req:read_part/3 in src/cowboy_req.erl accumulates incoming request bytes into a Buffer binary with no upper-bound check. When cow_multipart:parse_headers/2 returns more or {more, Buffer2}, the function reads up to Length bytes (default 64 KB) from the request body and recurses with the enlarged buffer. There is no equivalent of the byte_size(Acc) > Length guard present in the sibling function read_part_body/4. An unauthenticated attacker can send a multipart/form-data request whose body never yields a complete header section — for example, a body that never contains the advertised boundary delimiter, or one whose header lines never contain \\r\\n\\r\\n — and force the server process to accumulate memory linearly with the bytes the protocol layer is willing to deliver. A handful of concurrent such uploads is sufficient to exhaust BEAM memory. This issue affects cowboy from 2.0.0 before 2.15.0.",
    "evidence": "osv:CVE-2026-8466",
    "products": [],
    "severity": "high",
    "structured": {
      "id": "CVE-2026-8466",
      "aliases": [
        "CVE-2026-8466",
        "EEF-CVE-2026-8466",
        "GHSA-jfc2-q6qh-g5x8"
      ],
      "metrics": [
        {
          "type": "CVSS_V4",
          "score": "CVSS:4.0/AV:N/AC:L/AT:P/PR:N/UI:N/VC:N/VI:N/VA:H/SC:N/SI:N/SA:N"
        }
      ],
      "affected": [
        {
          "ranges": [
            {
              "repo": "https://github.com/ninenines/cowboy",
              "type": "GIT",
              "events": [
                {
                  "introduced": "917cf99e10c41676183d501b86af6e47c95afb89"
                },
                {
                  "fixed": "5c6a2061b41bb5771c4659fac7d5a822dca5bafb"
                },
                {
                  "introduced": "d3f15cfd8b2bb4c0c697bd995dfa4546474235ad"
                },
                {
                  "fixed": "3b9fb5214d70f1c4707a095c4193214bc12a7c36"
                }
              ],
              "database_specific": {
                "extracted_events": [
                  {
                    "range": [
                      {
                        "introduced": "917cf99e10c41676183d501b86af6e47c95afb89"
                      },
                      {
                        "fixed": "5c6a2061b41bb5771c4659fac7d5a822dca5bafb"
                      }
                    ],
                    "source": "AFFECTED_FIELD",
                    "strategy": "StandardRange"
                  },
                  {
                    "range": [
                      {
                        "introduced": "2.0.0"
                      },
                      {
                        "fixed": "2.15.0"
                      }
                    ],
                    "source": "AFFECTED_FIELD",
                    "strategy": "StandardRange"
                  },
                  {
                    "range": [
                      {
                        "fixed": "5c6a2061b41bb5771c4659fac7d5a822dca5bafb"
                      }
                    ],
                    "source": "REFERENCES_COMMIT"
                  }
                ]
              }
            }
          ],
          "versions": [
            "2.14.2",
            "2.14.1",
            "2.14.0",
            "2.13.0",
            "2.12.0",
            "2.11.0",
            "2.10.0",
            "2.9.0",
            "2.8.0",
            "2.7.0",
            "2.6.3",
            "2.6.2",
            "2.6.1",
            "2.6.0",
            "2.5.0",
            "2.4.0",
            "2.3.0",
            "2.2.2",
            "2.2.1",
            "2.2.0",
            "2.1.0",
            "2.0.0"
          ],
          "database_specific": {
            "source": "https://storage.googleapis.com/cve-osv-conversion/osv-output/CVE-2026-8466.json"
          }
        }
      ],
      "modified": "2026-10-28T02:30:53.342322866Z",
      "provider": "osv",
      "references": [
        "https://github.com",
        "https://osv.dev/vulnerability/EEF-CVE-2026-8466",
        "https://repo.hex.pm",
        "https://cna.erlef.org/cves/CVE-2026-8466.html",
        "https://github.com/CVEProject/cvelistV5/tree/main/cves/2026/8xxx/CVE-2026-8466.json",
        "https://nvd.nist.gov/vuln/detail/CVE-2026-8466",
        "https://github.com/ninenines/cowboy/commit/5c6a2061b41bb5771c4659fac7d5a822dca5bafb",
        "https://github.com/ninenines/cowboy"
      ],
      "provider_metadata": {
        "cwe_ids": [
          "CWE-770"
        ],
        "cna_assigner": "EEF",
        "osv_generated_from": "https://github.com/CVEProject/cvelistV5/tree/main/cves/2026/8xxx/CVE-2026-8466.json"
      }
    },
    "related_cves": [
      {
        "value": "CVE-2026-8466",
        "evidence": "/id"
      }
    ],
    "security_relevant": true,
    "severity_evidence": "/severity/0/score"
  },
  "source_id": "core-osv",
  "document_id": 522235,
  "published_at": "2026-05-13T18:26:21.089+00:00"
}