Tornado: Urlencoded body parsing omits max_num_fields, so one request can stall the event loop — GHSA-MPF4-983Q-P7J4

Summary

## Summary Tornado parses `application/x-www-form-urlencoded` bodies with `urllib.parse.parse_qs` and does not pass `max_num_fields`. A body made almost entirely of separators produces tens of millions of fields, and the parse happens on the event loop before the handler runs, so a single request stalls the whole server. ## Where it is `tornado/escape.py`, at HEAD `e530031405e2154654dedc4c84d5656b557ea310`:…

Timeline

Published by source

2026-09-02

Risk context

• Reported severity or threat level: high.
• Reported CVSS score: 7.5 out of 10.
• Reported EPSS value: 0.0035.
• Review exposure for the affected product or family: pip: tornado.

Product

pip: tornado

What to do

General, cautious steps (verify details in the official source):

• Prioritize patching or mitigation immediately (treat as actively risky).
• Identify affected product versions in your inventory and verify whether you are impacted.
• Apply vendor patches/updates or recommended mitigations as soon as available.
• Read the official advisory for exact affected versions and remediation steps.

Official advisory

• Read the official source
• CVE Record
• NVD

Evidence and provenance

Canonical advisory ID

GHSA-MPF4-983Q-P7J4

Source

GitHub

Vendor

GitHub

Published by source

2026-09-02

Last source activity

2026-09-02

Additional identifiers

CVE-2026-82397

Curated by

hlukh.ch

Related advisories and connections

These advisories are connected by shared CVE, product, vendor, source, or time signals.