{
  "affected": [
    {
      "ranges": [
        {
          "database_specific": {
            "extracted_events": [
              {
                "introduced": "0"
              },
              {
                "fixed": "6.5.8"
              }
            ],
            "source": [
              "AFFECTED_FIELD",
              "REFERENCES"
            ]
          },
          "events": [
            {
              "introduced": "0"
            },
            {
              "fixed": "8d6363ed7b69d5f0da806efe34d256627a2191de"
            },
            {
              "fixed": "a55abe3e3bf59994f29b2f7084c46341f0d4f6a7"
            }
          ],
          "repo": "https://github.com/tornadoweb/tornado",
          "type": "GIT"
        }
      ]
    }
  ],
  "aliases": [
    "GHSA-mpf4-983q-p7j4"
  ],
  "database_specific": {
    "cna_assigner": "GitHub_M",
    "cwe_ids": [
      "CWE-1284",
      "CWE-400"
    ],
    "osv_generated_from": "https://github.com/CVEProject/cvelistV5/tree/main/cves/2026/82xxx/CVE-2026-82397.json"
  },
  "details": "Tornado is a Python web framework and asynchronous networking library. Prior to 6.5.8, Tornado parses application/x-www-form-urlencoded request bodies with urllib.parse.parse_qs in tornado/escape.py without passing max_num_fields. RequestHandler._execute in tornado/web.py parses the body before handler dispatch through HTTPServerRequest._parse_body and parse_body_arguments in tornado/httputil.py, so an unauthenticated request body containing millions of separator-delimited fields can synchronously stall the single-threaded event loop and delay every connection. The body is bounded only by max_buffer_size, which defaults to 104857600 bytes. This issue is fixed in version 6.5.8.",
  "id": "CVE-2026-82397",
  "modified": "2026-09-02T03:30:41.088363950Z",
  "published": "2026-08-31T21:28:13.958Z",
  "references": [
    {
      "type": "WEB",
      "url": "https://github.com/tornadoweb/tornado/releases/tag/v6.5.8"
    },
    {
      "type": "ADVISORY",
      "url": "https://github.com/CVEProject/cvelistV5/tree/main/cves/2026/82xxx/CVE-2026-82397.json"
    },
    {
      "type": "ADVISORY",
      "url": "https://github.com/tornadoweb/tornado/security/advisories/GHSA-mpf4-983q-p7j4"
    },
    {
      "type": "ADVISORY",
      "url": "https://nvd.nist.gov/vuln/detail/CVE-2026-82397"
    },
    {
      "type": "FIX",
      "url": "https://github.com/tornadoweb/tornado/commit/8d6363ed7b69d5f0da806efe34d256627a2191de"
    },
    {
      "type": "FIX",
      "url": "https://github.com/tornadoweb/tornado/pull/3704"
    }
  ],
  "schema_version": "1.9.0",
  "severity": [
    {
      "score": "CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:H",
      "type": "CVSS_V3"
    }
  ],
  "summary": "Tornado: Urlencoded body parsing omits max_num_fields, so one request can stall the event loop"
}