Tornado is Vulnerable to Quadratic DoS via Crafted Multipart Parameters

MITRE NVD CVE.ORG JSON API

Summary

CVECVE-2025-67726
StatePUBLISHED
AssignerGitHub_M
Source PriorityCVE Program / NVD first with legacy fallback
Published2025-12-12 07:15:44 UTC
Updated2026-10-07 20:10:01 UTC
DescriptionTornado 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.

Risk And Classification

Primary CVSS: v3.1 7.5 HIGH from [email protected]

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

EPSS: 0.005350000 probability, percentile 0.433620000 (date 2026-10-07)

Problem Types: CWE-400 | CWE-834 | CWE-834 CWE-834: Excessive Iteration | CWE-400 CWE-400: Uncontrolled Resource Consumption

VersionSourceTypeScoreSeverityVector
3.1[email protected]Secondary7.5HIGHCVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:H
3.1CNADECLARED7.5HIGHCVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:H

CVSS v3.1 Breakdown

Attack Vector
Network
Attack Complexity
Low
Privileges Required
None
User Interaction
None
Scope
Unchanged
Confidentiality
None
Integrity
None
Availability
High

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

NVD Known Affected Configurations (CPE 2.3)

TypeVendorProductVersionUpdateEditionLanguage
Application Tornadoweb Tornado All All All All

Vendor Declared Affected Products

SourceVendorProductVersionPlatforms
CNA Tornadoweb Tornado affected < 6.5.3 Not specified

References

ReferenceSourceLinkTags
github.com/tornadoweb/tornado/security/advisories/GHSA-jhmp-mqwm-3gq8 [email protected] github.com Vendor Advisory
github.com/tornadoweb/tornado/commit/771472cfdaeebc0d89a9cc46e249f8891a6... [email protected] github.com Patch
github.com/tornadoweb/tornado/releases/tag/v6.5.3 [email protected] github.com Release Notes
CVE Program record CVE.ORG www.cve.org canonical
NVD vulnerability detail NVD nvd.nist.gov canonical, analysis

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