Description
Tornado is a Python web framework and asynchronous networking library. Versions 6.5.2 and below use an inefficient algorithm when parsing parameters for HTTP header values, potentially causing a DoS. The _parseparam function in httputil.py is used to parse specific HTTP header values, such as those in multipart/form-data and repeatedly calls string.count() within a nested loop while processing quoted semicolons. If an attacker sends a request with a large number of maliciously crafted parameters in a Content-Disposition header, the server's CPU usage increases quadratically (O(n²)) during parsing. Due to Tornado's single event loop architecture, a single malicious request can cause the entire server to become unresponsive for an extended period. This issue is fixed in version 6.5.3.
Published: 2025-12-12
Score: 7.5 High
EPSS: < 1% Very Low
KEV: No
Impact: n/a
Action: n/a
AI Analysis

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Remediation

No vendor fix or workaround currently provided.

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Tracking

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Advisories
Source ID Title
Debian DLA Debian DLA DLA-4461-1 python-tornado security update
Debian DSA Debian DSA DSA-6195-1 python-tornado security update
Ubuntu USN Ubuntu USN USN-7950-1 Tornado vulnerabilities
History

Mon, 22 Dec 2025 19:00:00 +0000

Type Values Removed Values Added
CPEs cpe:2.3:a:tornadoweb:tornado:*:*:*:*:*:*:*:*

Thu, 18 Dec 2025 19:15:00 +0000

Type Values Removed Values Added
Metrics ssvc

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

Sun, 14 Dec 2025 21:30:00 +0000

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

Sat, 13 Dec 2025 00:15:00 +0000

Type Values Removed Values Added
References
Metrics threat_severity

None

 threat_severity

Moderate

Fri, 12 Dec 2025 06:30:00 +0000

Type Values Removed Values Added
Description Tornado is a Python web framework and asynchronous networking library. Versions 6.5.2 and below use an inefficient algorithm when parsing parameters for HTTP header values, potentially causing a DoS. The _parseparam function in httputil.py is used to parse specific HTTP header values, such as those in multipart/form-data and repeatedly calls string.count() within a nested loop while processing quoted semicolons. If an attacker sends a request with a large number of maliciously crafted parameters in a Content-Disposition header, the server's CPU usage increases quadratically (O(n²)) during parsing. Due to Tornado's single event loop architecture, a single malicious request can cause the entire server to become unresponsive for an extended period. This issue is fixed in version 6.5.3.
Title Tornado is Vulnerable to Quadratic DoS via Crafted Multipart Parameters
Weaknesses CWE-400
CWE-834
References
Metrics cvssV3_1

{'score': 7.5, 'vector': 'CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:H'}

Subscriptions

Tornadoweb Tornado
cve-icon MITRE

Status: PUBLISHED

Assigner: GitHub_M

Published:

Updated: 2025-12-18T18:48:49.007Z

Reserved: 2025-12-10T19:25:20.819Z

Link: CVE-2025-67726

cve-icon Vulnrichment

Updated: 2025-12-18T18:48:01.134Z

cve-icon NVD

Status : Analyzed

Published: 2025-12-12T07:15:44.920

Modified: 2025-12-22T18:56:47.850

Link: CVE-2025-67726

cve-icon Redhat

Severity : Moderate

Publid Date: 2025-12-12T06:13:51Z

Links: CVE-2025-67726 - Bugzilla

cve-icon OpenCVE Enrichment

Updated: 2025-12-14T21:17:09Z

Weaknesses