PYSEC-2025-267

Vulnerability from pysec - Published: 2025-12-12 07:15 - Updated: 2026-07-13 05:52
VLAI
Details

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.

Severity
7.5 (High)
CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:H
Impacted products
Name purl
tornado pkg:pypi/tornado
Aliases
To clipboard 

{
  "affected": [
    {
      "ecosystem_specific": {},
      "package": {
        "ecosystem": "PyPI",
        "name": "tornado",
        "purl": "pkg:pypi/tornado"
      },
      "ranges": [
        {
          "events": [
            {
              "introduced": "0"
            },
            {
              "fixed": "6.5.3"
            }
          ],
          "type": "ECOSYSTEM"
        }
      ],
      "versions": [
        "0.2",
        "1.0",
        "1.1",
        "1.1.1",
        "1.2",
        "1.2.1",
        "2.0",
        "2.1",
        "2.1.1",
        "2.2",
        "2.2.1",
        "2.3",
        "2.4",
        "2.4.1",
        "3.0",
        "3.0.1",
        "3.0.2",
        "3.1",
        "3.1.1",
        "3.2",
        "3.2.1",
        "3.2.2",
        "4.0",
        "4.0.1",
        "4.0.2",
        "4.1",
        "4.1b2",
        "4.2",
        "4.2.1",
        "4.2b1",
        "4.3",
        "4.3b1",
        "4.3b2",
        "4.4",
        "4.4.1",
        "4.4.2",
        "4.4.3",
        "4.4b1",
        "4.5",
        "4.5.1",
        "4.5.2",
        "4.5.3",
        "4.5b1",
        "4.5b2",
        "5.0",
        "5.0.1",
        "5.0.2",
        "5.0a1",
        "5.0b1",
        "5.1",
        "5.1.1",
        "5.1b1",
        "6.0",
        "6.0.1",
        "6.0.2",
        "6.0.3",
        "6.0.4",
        "6.0a1",
        "6.0b1",
        "6.1",
        "6.1b1",
        "6.1b2",
        "6.2",
        "6.2b1",
        "6.2b2",
        "6.3",
        "6.3.1",
        "6.3.2",
        "6.3.3",
        "6.3b1",
        "6.4",
        "6.4.1",
        "6.4.2",
        "6.4b1",
        "6.5",
        "6.5.1",
        "6.5.2",
        "6.5b1"
      ]
    }
  ],
  "aliases": [
    "CVE-2025-67726",
    "GHSA-jhmp-mqwm-3gq8"
  ],
  "details": "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\u0027s CPU usage increases quadratically (O(n\u00b2)) during parsing. Due to Tornado\u0027s 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.",
  "id": "PYSEC-2025-267",
  "modified": "2026-07-13T05:52:14.026213Z",
  "published": "2025-12-12T07:15:44.920Z",
  "references": [
    {
      "type": "ADVISORY",
      "url": "https://github.com/tornadoweb/tornado/releases/tag/v6.5.3"
    },
    {
      "type": "ADVISORY",
      "url": "https://github.com/tornadoweb/tornado/security/advisories/GHSA-jhmp-mqwm-3gq8"
    },
    {
      "type": "FIX",
      "url": "https://github.com/tornadoweb/tornado/commit/771472cfdaeebc0d89a9cc46e249f8891a6b29cd"
    }
  ],
  "severity": [
    {
      "score": "CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:H",
      "type": "CVSS_V3"
    }
  ]
}



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