CVE-2025-67725

HIGH EPSS 31.5%
Published Dec 12, 20256mo ago · Modified Jun 17, 20261w ago
7.5 CVSS 3.1
High
Find Similar
Published Dec 12, 2025 6mo ago
Last Modified Jun 17, 2026 1w ago

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.

CVSS Details

Base Score
7.5
Exploitability
3.9
Impact
3.6
Vector string
CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:H
Attack Vector Network
Attack Complexity Low
Privileges Required None
User Interaction None
Scope Unchanged
Confidentiality None
Integrity None
Availability High

Threat Intelligence

EPSS Exploit Probability
31.5% percentile
Exploit & Patch Status
No Known Exploit
Patch Available

Weaknesses 1

CWE-400 Uncontrolled Resource Consumption Resource Mgmt

Affected Products 1

VendorProductVersionRange
tornadowebtornado* <6.5.3

References 3

  • github.com https://github.com/tornadoweb/tornado/commit/771472cfdaeebc0d89a9cc46e249f8891a6b29cd
    Patch
  • github.com https://github.com/tornadoweb/tornado/releases/tag/v6.5.3
    Release Notes
  • github.com https://github.com/tornadoweb/tornado/security/advisories/GHSA-c98p-7wgm-6p64
    Vendor Advisory

Remediation

  • github.com https://github.com/tornadoweb/tornado/commit/771472cfdaeebc0d89a9cc46e249f8891a6b29cd
    Patch