High 7.5Published Aug 31, 2026

CVE-2026-82397Tornado: Urlencoded body parsing omits max_num_fields, so one request can stall the event loop

Updated under an hour ago (2026-10-19 07:10 UTC)

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No exploitation reported and no EPSS estimate yet.

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Every CVE for tornadoweb tornado

Exploited in the last 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.

CVSS: 7.5 HIGH (v3.1, CNA)CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:H
Weakness (CWE): CWE-400, CWE-1284
Known exploited: Not in CISA's KEV catalog
EPSS (exploitation in the next 30 days): Not loaded for this CVE
Assigned by: GitHub_M
NVD analysis: Deferred
Record last updated: Sep 2, 2026
First seen by InfoSec Signals: Oct 9, 2026

Affected products

Affected products

tornadoweb tornado tornadoweb:tornado (from the name)	before 6.5.8	CNA record

References

https://github.com/tornadoweb/tornado/security/advisories/GHSA-mpf4-983q-p7j4x-refsource-confirm
https://github.com/tornadoweb/tornado/pull/3704x-refsource-misc
https://github.com/tornadoweb/tornado/commit/8d6363ed7b69d5f0da806efe34d256627a2191dex-refsource-misc
https://github.com/tornadoweb/tornado/releases/tag/v6.5.8x-refsource-misc

The CVE record on cve.org NVD's entry

The CVE record is authoritative. Products marked “from the name” were identified from the CNA's free-text names, not a CPE, and are matched less certainly. This product uses the NVD API but is not endorsed or certified by the NVD.