HTTP/1 chunked body reader ignores length cap in bandit

{
  "id": "18d703ed7c5b2404d2302788b2679caaaa5ef74317946ee9c90797f225ca02ee",
  "url": "https://osv.dev/vulnerability/CVE-2026-39803",
  "method": "structured",
  "payload": {
    "kind": "advisory",
    "title": "HTTP/1 chunked body reader ignores length cap in bandit",
    "summary": "Allocation of Resources Without Limits or Throttling vulnerability in mtrudel bandit allows unauthenticated remote denial of service via memory exhaustion. The chunked clause of 'Elixir.Bandit.HTTP1.Socket':read_data/2 in lib/bandit/http1/socket.ex ignores the caller-supplied :length option when reading HTTP/1 chunked request bodies. Instead of capping the accumulated body at the configured limit (e.g. Plug.Parsers' default 8 MB), do_read_chunked_data!/5 buffers every received chunk into an iolist unconditionally and materializes the entire body as a single binary. The function always returns {:ok, body, ...}, so callers cannot interpose a 413 response. Because Plug.Parsers runs before routing and authentication in the standard Phoenix endpoint, an unauthenticated attacker needs no valid route or credentials. Sending a single Transfer-Encoding: chunked POST request with an arbitrarily large body to any path causes the BEAM process to exhaust available memory and be terminated by the OS OOM killer. The content-length path in the same function correctly enforces the limit and is not affected. This issue affects bandit: from 1.4.0 before 1.11.1.",
    "evidence": "osv:CVE-2026-39803",
    "products": [],
    "severity": "high",
    "structured": {
      "id": "CVE-2026-39803",
      "aliases": [
        "CVE-2026-39803",
        "EEF-CVE-2026-39803",
        "GHSA-9q9q-324x-93r2"
      ],
      "metrics": [
        {
          "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": [
        {
          "ranges": [
            {
              "repo": "https://github.com/mtrudel/bandit",
              "type": "GIT",
              "events": [
                {
                  "introduced": "e5d4262b07b3e1026c57647b281dccfababea13b"
                },
                {
                  "fixed": "40a1b8fc924694a0125bbaa7fee101fa43feeb52"
                },
                {
                  "fixed": "ae3520dfdbfab115c638f8c7f6f6b805db34e1ab"
                }
              ],
              "database_specific": {
                "extracted_events": [
                  {
                    "cpe": "cpe:2.3:a:mtrudel:bandit:*:*:*:*:*:*:*:*",
                    "range": [
                      {
                        "introduced": "1.4.0"
                      },
                      {
                        "fixed": "1.11.1"
                      }
                    ],
                    "source": "CPE_RANGE"
                  },
                  {
                    "range": [
                      {
                        "fixed": "ae3520dfdbfab115c638f8c7f6f6b805db34e1ab"
                      }
                    ],
                    "source": "REFERENCES_COMMIT"
                  }
                ]
              }
            }
          ],
          "versions": [
            "1.11.0",
            "1.10.4",
            "1.10.3",
            "1.10.2",
            "1.10.1",
            "1.10.0",
            "1.9.0",
            "1.8.0",
            "1.7.0",
            "1.6.11",
            "1.6.10",
            "1.6.9",
            "1.6.8",
            "1.6.7",
            "1.6.6",
            "1.6.5",
            "1.6.4",
            "1.6.3",
            "1.6.2",
            "1.6.1",
            "1.6.0",
            "1.5.7",
            "1.5.6",
            "1.5.5",
            "1.5.4",
            "1.5.3",
            "1.5.2",
            "1.5.1",
            "1.5.0",
            "1.4.2",
            "1.4.1",
            "1.4.0"
          ],
          "database_specific": {
            "source": "https://storage.googleapis.com/cve-osv-conversion/osv-output/CVE-2026-39803.json"
          }
        }
      ],
      "modified": "2026-10-28T02:30:26.083700853Z",
      "provider": "osv",
      "references": [
        "https://cna.erlef.org/cves/CVE-2026-39803.html",
        "https://github.com",
        "https://osv.dev/vulnerability/EEF-CVE-2026-39803",
        "https://repo.hex.pm",
        "https://github.com/CVEProject/cvelistV5/tree/main/cves/2026/39xxx/CVE-2026-39803.json",
        "https://github.com/mtrudel/bandit/security/advisories/GHSA-9q9q-324x-93r2",
        "https://nvd.nist.gov/vuln/detail/CVE-2026-39803",
        "https://github.com/mtrudel/bandit/commit/ae3520dfdbfab115c638f8c7f6f6b805db34e1ab",
        "https://github.com/mtrudel/bandit"
      ],
      "provider_metadata": {
        "cwe_ids": [
          "CWE-770"
        ],
        "cna_assigner": "EEF",
        "osv_generated_from": "https://github.com/CVEProject/cvelistV5/tree/main/cves/2026/39xxx/CVE-2026-39803.json"
      }
    },
    "related_cves": [
      {
        "value": "CVE-2026-39803",
        "evidence": "/id"
      }
    ],
    "security_relevant": true,
    "severity_evidence": "/severity/0/score"
  },
  "source_id": "core-osv",
  "document_id": 492287,
  "published_at": "2026-05-13T13:36:09.648+00:00"
}