CVE-2026-82397

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.

Scores

Faiblesses (CWE)

• CWE-400
• CWE-1284

Avis

• GHSA-mpf4-983q-p7j4 — Tornado: Urlencoded body parsing omits max_num_fields, so one request can stall the event loop
• PYSEC-2026-3928 — Tornado: Urlencoded body parsing omits max_num_fields, so one request can stall the event loop

Références européennes

• ENISA EUVD · EUVD-2026-68892
• GCVE · GCVE-0-2026-82397

Avis du CERT-FR

• CERTFR-2026-AVI-1233 — Multiples vulnérabilités dans les produits IBM · cert.ssi.gouv.fr

Produits affectés

Références

• 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

Sources