{"id":"CVE-2026-31958","aliases":["GHSA-qjxf-f2mg-c6mc","PYSEC-2026-140"],"url":"https://o3.security/vulnerability/CVE-2026-31958","summary":"Tornado has a DoS due to too many multipart parts","details":"In versions of Tornado prior to 6.5.5, the only limit on the number of parts in `multipart/form-data` is the `max_body_size` setting (default 100MB). Since parsing occurs synchronously on the main thread, this creates the possibility of denial-of-service due to the cost of parsing very large multipart bodies with many parts. \n\nTornado 6.5.5 introduces new limits on the size and complexity of multipart bodies, including a default limit of 100 parts per request. These limits are configurable if needed; see `tornado.httputil.ParseMultipartConfig`. It is also now possible to disable `multipart/form-data` parsing entirely if it is not required for the application.","published":"2026-03-11T19:27:23.380Z","modified":"2026-10-28T02:31:02.859418713Z","cvss":null,"epss":null,"cisaKev":null,"exploitsKnown":0,"affectedPackages":[{"ecosystem":"PyPI","name":"tornado","fixedVersion":"6.5.5"}],"fix":{"url":"https://github.com/tornadoweb/tornado/commit/119a195e290c43ad2d63a2cf012c29d43d6ed839","label":"tornadoweb/tornado@119a195"},"references":[{"type":"WEB","url":"https://lists.debian.org/debian-lts-announce/2026/04/msg00000.html"},{"type":"ADVISORY","url":"https://github.com/CVEProject/cvelistV5/tree/main/cves/2026/31xxx/CVE-2026-31958.json"},{"type":"ADVISORY","url":"https://github.com/tornadoweb/tornado/security/advisories/GHSA-qjxf-f2mg-c6mc"},{"type":"ADVISORY","url":"https://nvd.nist.gov/vuln/detail/CVE-2026-31958"},{"type":"WEB","url":"https://github.com/tornadoweb/tornado/commit/119a195e290c43ad2d63a2cf012c29d43d6ed839"},{"type":"WEB","url":"https://github.com/pypa/advisory-database/tree/main/vulns/tornado/PYSEC-2026-140.yaml"},{"type":"PACKAGE","url":"https://github.com/tornadoweb/tornado"},{"type":"WEB","url":"https://github.com/tornadoweb/tornado/releases/tag/v6.5.5"}],"provenance":{"sources":["OSV.dev","FIRST.org (EPSS)"],"lastVerified":"2026-10-28T02:31:02.859418713Z"}}