CVE-2026-82397: Tornadoweb Tornado

High severity, CVSS 7.5. EPSS: 0.3% chance of exploitation in the next 30 days.

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 products

• Tornadoweb Tornado: before 6.5.8 (fixed in 6.5.8)

Published 2026-08-31. Last modified 2026-09-09.