CVE-2025-67726Network attack vector

Server hang via quadratic multipart parameter parsing

Published Dec 12, 2025 · Updated Dec 12, 2025

Denial of service in tornadoweb Tornado before 6.5.3 allows remote attackers to hang the server via crafted multipart parameters. The _parseparam function in httputil.py repeatedly counts quotes across growing prefixes while scanning quoted semicolons, producing O(n²) CPU work. A single unauthenticated multipart request can monopolize Tornado's single event loop, leaving the application unresponsive for an extended period.

CVSS severity7.5
High
EPSS probability0.53%
Next 30 days · Sep 16, 2026
Known exploitationUnconfirmed
Based on sourced intelligence
Hinoki checkNot available
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Summary

What happened

Denial of service in tornadoweb Tornado before 6.5.3 allows remote attackers to hang the server via crafted multipart parameters. The _parseparam function in httputil.py repeatedly counts quotes across growing prefixes while scanning quoted semicolons, producing O(n²) CPU work. A single unauthenticated multipart request can monopolize Tornado's single event loop, leaving the application unresponsive for an extended period.

The record

CVE
CVE-2025-67726
Published
Dec 12, 2025
Updated
Dec 12, 2025
Vendor
tornadoweb
Product
Tornado
Classifications
CWE-400, CWE-834, T1499.004
Attack vector
network
Privileges
unauthenticated

Timeline

How it unfolded

  1. Dec 12, 2025CVE publishedPublication date reported by the CVE source.
  2. Dec 12, 2025Record updatedLatest update available in the CVE record.

Exploitability

Present is not the same as exploitable

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Is a vulnerable build present?

Compare these published version ranges with your installed build and any vendor patches.

  1. Affected versionversion=< 6.5.3

What conditions does exploitation require?

Attack vectornetwork
Required privilegesunauthenticated

What is affected?

tornadoweb · Tornadoversion=< 6.5.3

Published CVSS scores

7.5GitHubCVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:H

CVSS describes severity. EPSS estimates exploitation probability.

Attacks

What attackers are doing with it

Daily unique IPs observed by Shadowserver honeypots for known exploited vulnerabilities (KEVs). Missing observations do not establish an absence of attacks.

Daily unique IPsNo honeypot observations are available for this CVE in the selected window.

No observations available

Sep 9, 2026Sep 15, 2026
Latest reporting daySep 15, 2026
Latest daily unique IPsUnavailable
Prior 30-day averageUnavailable
SourceShadowserver honeypots (KEV)
Vectornetwork
Privilegesunauthenticated
Known exploitationUnconfirmed
Public exploitUnconfirmed

Weakness, pattern, technique

CWE-400Uncontrolled Resource Consumption
CWE-834Excessive Iteration
T1499.004Application or System Exploitation

Public exploit references

No public exploit references are available in this record.

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Technologies

Your stack

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Your stack

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