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CVE-2025-67725— Tornado is Vulnerable to Quadratic DoS via Repeated Header Coalescing

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及之前版本存在资源管理错误漏洞，该漏洞源于HTTPHeaders.add方法存在字符串连接问题，可能导致拒绝服务攻击。

CVSS 7.5 · High EPSS 0.56% · P45

Possible ATT&CK Techniques 1 AI

T1499 · Endpoint Denial of Service
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I. Basic Information for CVE-2025-67725

Vulnerability Information
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Vulnerability Title
Tornado is Vulnerable to Quadratic DoS via Repeated Header Coalescing
Source: CVE Program / CVE List V5
Vulnerability Description
Tornado is a Python web framework and asynchronous networking library. In versions 6.5.2 and below, a single maliciously crafted HTTP request can block the server's event loop for an extended period, caused by the HTTPHeaders.add method. The function accumulates values using string concatenation when the same header name is repeated, causing a Denial of Service (DoS). Due to Python string immutability, each concatenation copies the entire string, resulting in O(n²) time complexity. The severity can vary from high if max_header_size has been increased from its default, to low if it has its default value of 64KB. 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
未加控制的资源消耗(资源穷尽)
Source: CVE Program / CVE List V5
Vulnerability Title
Tornado 资源管理错误漏洞
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及之前版本存在资源管理错误漏洞，该漏洞源于HTTPHeaders.add方法存在字符串连接问题，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-2025-67725

# POC Description Source Link Shenlong Link
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Qwen3.6-35B-A3B · 8740 chars
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III. Intelligence Information for CVE-2025-67725

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Patches & Fixes for CVE-2025-67725 (1)

Vendor Advisories for CVE-2025-67725 (1)

Other References for CVE-2025-67725 (1)

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

CVE-2025-67726 7.5 HIGH Tornado is Vulnerable to Quadratic DoS via Crafted Multipart Parameters
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-400

V. Comments for CVE-2025-67725

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