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CVE-2025-67726— Tornado is Vulnerable to Quadratic DoS via Crafted Multipart Parameters

Quick assessment

Affected
tornadoweb tornado
Exploitation
Public or AI PoC available; prioritize validation
Recommended action
Check the vendor advisory and references for a fixed version. If immediate upgrade is impossible, restrict exposure and increase monitoring.

Tornado是中国龙卷风科技（Tornado）社区的一个Python Web框架和异步网络库。该库通过使用非阻塞网络I / O，可以扩展到成千上万的开放连接，使其非常适合 长时间轮询， WebSocket和其他需要与每个用户建立长期连接的应用程序。 Tornado 6.5.2及之前版本存在安全漏洞，该漏洞源于解析HTTP头参数时使用低效算法，可能导致拒绝服务攻击。

CVSS 7.5 · High EPSS 0.53% · P43
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I. Basic Information for CVE-2025-67726

Vulnerability Information
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Vulnerability Title
Tornado is Vulnerable to Quadratic DoS via Crafted Multipart Parameters
Source: CVE Program / CVE List V5
Vulnerability 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.
Source: CVE Program / CVE List V5
CVSS Information
CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:H
Source: CVE Program / CVE List V5
Vulnerability Type
过度迭代
Source: CVE Program / CVE List V5
Vulnerability Title
Tornado 安全漏洞
Source: CNNVD (China National Vulnerability Database)
Vulnerability Description
Tornado是中国龙卷风科技（Tornado）社区的一个Python Web框架和异步网络库。该库通过使用非阻塞网络I / O，可以扩展到成千上万的开放连接，使其非常适合 长时间轮询， WebSocket和其他需要与每个用户建立长期连接的应用程序。 Tornado 6.5.2及之前版本存在安全漏洞，该漏洞源于解析HTTP头参数时使用低效算法，可能导致拒绝服务攻击。
Source: CNNVD (China National Vulnerability Database)
CVSS Information
N/A
Source: CNNVD (China National Vulnerability Database)
Vulnerability Type
N/A
Source: CNNVD (China National Vulnerability Database)

Affected Products

Vendor Product Affected Versions CPE Subscribe
tornadoweb tornado < 6.5.3 -

II. Public POCs for CVE-2025-67726

# POC Description Source Link Shenlong Link
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Qwen3.6-35B-A3B · 7255 chars
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III. Intelligence Information for CVE-2025-67726

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Patches & Fixes for CVE-2025-67726 (1)

Vendor Advisories for CVE-2025-67726 (1)

Other References for CVE-2025-67726 (1)

Same Patch Batch · tornadoweb · 2025-12-12 · 3 CVEs total

CVE-2025-67725 7.5 HIGH Tornado is Vulnerable to Quadratic DoS via Repeated Header Coalescing
CVE-2025-67724 5.4 MEDIUM Tornado vulnerable to Header Injection and XSS via reason argument

IV. Related Vulnerabilities

Same product: tornado
Same vendor: tornadoweb
Same weakness: CWE-834

V. Comments for CVE-2025-67726

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