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Vulnerability record · CVE-2026-82397 · published 31 August 2026

CVE-2026-82397: Uncontrolled resource consumption vulnerability

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.

7.5 CVSS 3.1 High EPSS 0.63% · top 51.9% CWE-400 · Uncontrolled resource consumptionCWE-1284 · CWE-1284 Deferred
7.5CVSS 3.1 base score
0.63%EPSS exploitation probability, 30 days
NoNot in CISA KEV
0Affected product versions listed by NVD
4References
9 Sep 2026Last modified by NVD

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.

CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:H

References

LinkTags
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

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Source: NIST National Vulnerability Database (record CVE-2026-82397), CISA KEV, FIRST EPSS (scores of 2026-09-26). This page is refreshed as NVD updates the record.