Tornado is a Python web framework and asynchronous networking library. In versions of Tornado prior to 6.5.5, the only limit on the number of parts in multipart/form-data is the max_body_size setting (default 100MB). Since parsing occurs synchronously on the main thread, this creates the possibility of denial-of-service due to the cost of parsing very large multipart bodies with many parts. This vulnerability is fixed in 6.5.5.
History

Fri, 13 Mar 2026 00:15:00 +0000

Type Values Removed Values Added
Weaknesses CWE-770
References
Metrics threat_severity

None

cvssV3_1

{'score': 5.3, 'vector': 'CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:L'}

threat_severity

Moderate


Thu, 12 Mar 2026 20:15:00 +0000

Type Values Removed Values Added
Metrics ssvc

{'options': {'Automatable': 'yes', 'Exploitation': 'none', 'Technical Impact': 'partial'}, 'version': '2.0.3'}


Thu, 12 Mar 2026 10:15:00 +0000

Type Values Removed Values Added
First Time appeared Tornadoweb
Tornadoweb tornado
Vendors & Products Tornadoweb
Tornadoweb tornado

Wed, 11 Mar 2026 19:45:00 +0000

Type Values Removed Values Added
Description Tornado is a Python web framework and asynchronous networking library. In versions of Tornado prior to 6.5.5, the only limit on the number of parts in multipart/form-data is the max_body_size setting (default 100MB). Since parsing occurs synchronously on the main thread, this creates the possibility of denial-of-service due to the cost of parsing very large multipart bodies with many parts. This vulnerability is fixed in 6.5.5.
Title Tornado has a DoS due to too many multipart parts
Weaknesses CWE-400
References
Metrics cvssV4_0

{'score': 8.7, 'vector': 'CVSS:4.0/AV:N/AC:L/AT:N/PR:N/UI:N/VC:N/VI:N/VA:H/SC:N/SI:N/SA:N'}


cve-icon MITRE

Status: PUBLISHED

Assigner: GitHub_M

Published: 2026-03-11T19:27:23.380Z

Updated: 2026-03-12T19:55:50.969Z

Reserved: 2026-03-10T15:40:10.481Z

Link: CVE-2026-31958

cve-icon Vulnrichment

Updated: 2026-03-12T19:55:47.727Z

cve-icon NVD

Status : Awaiting Analysis

Published: 2026-03-11T20:16:16.617

Modified: 2026-03-12T21:08:22.643

Link: CVE-2026-31958

cve-icon Redhat

Severity : Moderate

Publid Date: 2026-03-11T19:27:23Z

Links: CVE-2026-31958 - Bugzilla