# CVE-2026-82397

## Summary

- **CVE ID:** CVE-2026-82397
- **Severity:** HIGH
- **CVSS Score:** 7.5 (CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:H)
- **CWE:** CWE-400, CWE-1284
- **Published:** Aug 31, 2026
- **Last Modified:** Sep 2, 2026

## 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.

## Affected Products

- tornadoweb — tornado (< 6.5.8)

## References

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

## Exploitation Prediction (EPSS)

- **EPSS Score:** 0.35%
- **EPSS Percentile:** 28.2

---
_Exported from OnDuty AI Vulnerability Intelligence on 2026-09-11._