{"id":"CVE-2026-82397","state":"PUBLISHED","title":"Tornado: Urlencoded body parsing omits max_num_fields, so one request can stall the event loop","description":"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.","publishedAt":"2026-08-31T21:28:13.958Z","updatedAt":"2026-09-02T17:39:41.238Z","severity":{"score":7.5,"label":"High","version":"3.1","vector":"CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:H","source":"GitHub_M"},"assigner":"GitHub_M","products":["tornadoweb tornado"],"affected":[{"vendor":"tornadoweb","product":"tornado","versions":[{"version":"< 6.5.8","status":"affected"}]}],"references":["https://github.com/tornadoweb/tornado/security/advisories/GHSA-mpf4-983q-p7j4","https://github.com/tornadoweb/tornado/pull/3704","https://github.com/tornadoweb/tornado/commit/8d6363ed7b69d5f0da806efe34d256627a2191de","https://github.com/tornadoweb/tornado/releases/tag/v6.5.8"],"weaknesses":["CWE-400","CWE-1284"],"ingestedAt":"2026-10-29T20:13:15.269Z","source":{"repository":"CVEProject/cvelistV5","path":"cves/2026/82xxx/CVE-2026-82397.json","commit":"556c9d3a8cd17e218bb8e452ba7cd619a384ff47"},"raw":{"dataType":"CVE_RECORD","dataVersion":"5.2","cveMetadata":{"cveId":"CVE-2026-82397","state":"PUBLISHED","datePublished":"2026-08-31T21:28:13.958Z","dateUpdated":"2026-09-02T17:39:41.238Z","assignerShortName":"GitHub_M","assignerOrgId":"a0819718-46f1-4df5-94e2-005712e83aaa","dateReserved":"2026-08-28T22:00:43.512Z"},"containers":{"cna":{"title":"Tornado: Urlencoded body parsing omits max_num_fields, so one request can stall the event loop","descriptions":[{"lang":"en","value":"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."}],"affected":[{"vendor":"tornadoweb","product":"tornado","versions":[{"version":"< 6.5.8","status":"affected"}]}],"references":[{"url":"https://github.com/tornadoweb/tornado/security/advisories/GHSA-mpf4-983q-p7j4","name":"https://github.com/tornadoweb/tornado/security/advisories/GHSA-mpf4-983q-p7j4","tags":["x_refsource_CONFIRM"]},{"url":"https://github.com/tornadoweb/tornado/pull/3704","name":"https://github.com/tornadoweb/tornado/pull/3704","tags":["x_refsource_MISC"]},{"url":"https://github.com/tornadoweb/tornado/commit/8d6363ed7b69d5f0da806efe34d256627a2191de","name":"https://github.com/tornadoweb/tornado/commit/8d6363ed7b69d5f0da806efe34d256627a2191de","tags":["x_refsource_MISC"]},{"url":"https://github.com/tornadoweb/tornado/releases/tag/v6.5.8","name":"https://github.com/tornadoweb/tornado/releases/tag/v6.5.8","tags":["x_refsource_MISC"]}],"metrics":[{"cvssV3_1":{"attackComplexity":"LOW","attackVector":"NETWORK","availabilityImpact":"HIGH","baseScore":7.5,"baseSeverity":"HIGH","confidentialityImpact":"NONE","integrityImpact":"NONE","privilegesRequired":"NONE","scope":"UNCHANGED","userInteraction":"NONE","vectorString":"CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:H","version":"3.1"}}],"problemTypes":[{"descriptions":[{"cweId":"CWE-400","lang":"en","description":"CWE-400: Uncontrolled Resource Consumption","type":"CWE"}]},{"descriptions":[{"cweId":"CWE-1284","lang":"en","description":"CWE-1284: Improper Validation of Specified Quantity in Input","type":"CWE"}]}],"providerMetadata":{"shortName":"GitHub_M","orgId":"a0819718-46f1-4df5-94e2-005712e83aaa","dateUpdated":"2026-08-31T21:28:13.958Z"},"source":{"advisory":"GHSA-mpf4-983q-p7j4","discovery":"UNKNOWN"}},"adp":[{"title":"CISA ADP Vulnrichment","metrics":[{"other":{"type":"ssvc","content":{"timestamp":"2026-09-02T17:39:28.982654Z","id":"CVE-2026-82397","options":[{"Exploitation":"none"},{"Automatable":"yes"},{"Technical Impact":"partial"}],"role":"CISA Coordinator","version":"2.0.3"}}}],"providerMetadata":{"shortName":"CISA-ADP","orgId":"134c704f-9b21-4f2e-91b3-4a467353bcc0","dateUpdated":"2026-09-02T17:39:41.238Z"}}]}}}