CVE-2026-82397

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.

• CWE-400
• CWE-1284

• https://github.com/tornadoweb/tornado/commit/8d6363ed7b69d5f0da806efe34d256627a2191de
• https://github.com/tornadoweb/tornado/pull/3704
• https://github.com/tornadoweb/tornado/releases/tag/v6.5.8
• https://github.com/tornadoweb/tornado/security/advisories/GHSA-mpf4-983q-p7j4

Published

Aug 31, 2026

Last Modified

Sep 9, 2026

Status

Deferred

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