CVE catalog

CVE-2025-67726

Tornado vulnerabilities

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: High · CVSS 7.5CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:H
Published: Dec 12, 2025, 6:13:51 AM UTC
Source: [NVD] · [CVE record]
EPSS: 0.53% · Oct 27, 2026

Projects and upstream resources

[python-tornado][Source-reported homepage]

Reported versions and fixes

Each observation applies to its named package, distribution, and release. Distribution backports can fix a vulnerability while retaining an older upstream version number.

Version impact has not been established. The original provider fields are retained below.

Provider details and historical evidence

Original provider fields

{
  "package_releases": [
    {
      "name": "python-tornado",
      "status": "fixed",
      "release": "sid",
      "version": "6.5.5-5"
    },
    {
      "name": "python-tornado",
      "status": "fixed",
      "release": "forky",
      "version": "6.5.5-5"
    },
    {
      "name": "python-tornado",
      "status": "fixed",
      "release": "trixie",
      "version": "6.4.2-3+deb13u2"
    },
    {
      "name": "python-tornado",
      "status": "fixed",
      "release": "trixie-security",
      "version": "6.4.2-3+deb13u2"
    },
    {
      "name": "python-tornado",
      "status": "fixed",
      "release": "bookworm",
      "version": "6.2.0-3+deb12u4"
    },
    {
      "name": "python-tornado",
      "status": "fixed",
      "release": "bookworm-security",
      "version": "6.2.0-3+deb12u4"
    }
  ],
  "fixed_versions": [
    {
      "bug": 1122663,
      "name": "python-tornado",
      "type": "source",
      "origin": null,
      "release": "sid",
      "urgency": "not yet assigned",
      "fixed_version": "6.5.4-0.1"
    },
    {
      "bug": 1122663,
      "name": "python-tornado",
      "type": "source",
      "origin": null,
      "release": "forky",
      "urgency": "not yet assigned",
      "fixed_version": "6.5.4-0.1"
    },
    {
      "bug": 1122663,
      "name": "python-tornado",
      "type": "source",
      "origin": null,
      "release": "trixie",
      "urgency": "not yet assigned",
      "fixed_version": "6.4.2-3+deb13u2"
    },
    {
      "bug": 1122663,
      "name": "python-tornado",
      "type": "source",
      "origin": null,
      "release": "bookworm",
      "urgency": "not yet assigned",
      "fixed_version": "6.2.0-3+deb12u4"
    }
  ],
  "distribution_packages": [
    {
      "name": "python-tornado",
      "distro": "ubuntu",
      "release": "noble",
      "ecosystem": "deb",
      "fixed_version": "not yet fixed"
    },
    {
      "name": "python-tornado",
      "distro": "ubuntu",
      "release": "noble",
      "ecosystem": "deb",
      "fixed_version": "6.4.0-1ubuntu0.4"
    },
    {
      "name": "python-tornado-doc",
      "distro": "ubuntu",
      "release": "noble",
      "ecosystem": "deb",
      "fixed_version": "6.4.0-1ubuntu0.4"
    },
    {
      "name": "python3-tornado",
      "distro": "ubuntu",
      "release": "noble",
      "ecosystem": "deb",
      "fixed_version": "6.4.0-1ubuntu0.4"
    },
    {
      "name": "tornado",
      "ecosystem": "pip",
      "fixed_version": "6.5.3"
    },
    {
      "name": "tornado",
      "ranges": [
        {
          "fixed": "6.5.3",
          "introduced": "",
          "last_affected": "",
          "start_excluding": ""
        }
      ],
      "ecosystem": "cpe",
      "fixed_version": "6.5.3",
      "provider_record_id": "NVD-CVE-2025-67726"
    },
    {
      "name": "python-tornado",
      "distro": "ubuntu",
      "ranges": [
        {
          "type": "ECOSYSTEM",
          "events": [
            {
              "introduced": "0"
            },
            {
              "fixed": "6.1.0-3ubuntu0.1~esm4"
            }
          ]
        }
      ],
      "release": "pro",
      "versions": [
        "6.1.0-1build1",
        "6.1.0-2",
        "6.1.0-3",
        "6.1.0-3build1",
        "6.1.0-3ubuntu0.1~esm1",
        "6.1.0-3ubuntu0.1~esm2"
      ],
      "ecosystem": "deb",
      "fixed_version": "6.1.0-3ubuntu0.1~esm4",
      "provider_record_id": "UBUNTU-CVE-2025-67726"
    },
    {
      "name": "python-tornado",
      "distro": "ubuntu",
      "ranges": [
        {
          "type": "ECOSYSTEM",
          "events": [
            {
              "introduced": "0"
            },
            {
              "fixed": "6.4.0-1ubuntu0.4"
            }
          ]
        }
      ],
      "release": "24.04",
      "versions": [
        "6.3.2-1",
        "6.4.0-0ubuntu1",
        "6.4.0-1",
        "6.4.0-1build1",
        "6.4.0-1ubuntu0.1",
        "6.4.0-1ubuntu0.2"
      ],
      "ecosystem": "deb",
      "fixed_version": "6.4.0-1ubuntu0.4",
      "provider_record_id": "UBUNTU-CVE-2025-67726"
    },
    {
      "name": "python-tornado",
      "distro": "ubuntu",
      "ranges": [
        {
          "type": "ECOSYSTEM",
          "events": [
            {
              "introduced": "0"
            },
            {
              "fixed": "6.4.2-3ubuntu0.2"
            }
          ]
        }
      ],
      "release": "25.10",
      "versions": [
        "6.4.2-1",
        "6.4.2-2",
        "6.4.2-2ubuntu1",
        "6.4.2-3"
      ],
      "ecosystem": "deb",
      "fixed_version": "6.4.2-3ubuntu0.2",
      "provider_record_id": "UBUNTU-CVE-2025-67726"
    }
  ]
}

[Debian bug #1122663]

OpenFactory catalog packages

Matching against OpenFactory catalog package versions is in progress.

[Debian 12 (Bookworm)]

[python3-tornado]Unknown
Source package: [python-tornado]
Details (4)
- 6.2.0-3+deb12u4 · amd64 · bookworm
  Fixed · Fixed: 6.2.0-3+deb12u4
  usn · python-tornado · debian · bookworm; usn · python-tornado · debian · 12
- 6.2.0-3+deb12u4 · arm64 · bookworm
  Fixed · Fixed: 6.2.0-3+deb12u4
  usn · python-tornado · debian · bookworm; usn · python-tornado · debian · 12
- 6.2.0-3+deb12u4 · amd64 · bookworm-security
  Fixed · Fixed: 6.2.0-3+deb12u4
  usn · python-tornado · debian · bookworm; usn · python-tornado · debian · 12
- 6.2.0-3+deb12u4 · arm64 · bookworm-security
  Fixed · Fixed: 6.2.0-3+deb12u4
  usn · python-tornado · debian · bookworm; usn · python-tornado · debian · 12
[python-tornado-doc]Unknown
Source package: [python-tornado]
Details (4)
- 6.2.0-3+deb12u4 · all · bookworm
  Fixed · Fixed: 6.2.0-3+deb12u4
  usn · python-tornado · debian · bookworm; usn · python-tornado · debian · 12
- 6.2.0-3+deb12u4 · all · bookworm
  Fixed · Fixed: 6.2.0-3+deb12u4
  usn · python-tornado · debian · bookworm; usn · python-tornado · debian · 12
- 6.2.0-3+deb12u4 · all · bookworm-security
  Fixed · Fixed: 6.2.0-3+deb12u4
  usn · python-tornado · debian · bookworm; usn · python-tornado · debian · 12
- 6.2.0-3+deb12u4 · all · bookworm-security
  Fixed · Fixed: 6.2.0-3+deb12u4
  usn · python-tornado · debian · bookworm; usn · python-tornado · debian · 12

[Debian 13 (Trixie)]

[python3-tornado]Unknown
Source package: [python-tornado]
Details (4)
- 6.4.2-3+deb13u2 · amd64 · trixie
  Fixed · Fixed: 6.4.2-3+deb13u2
  usn · python-tornado · debian · 13
- 6.4.2-3+deb13u2 · arm64 · trixie
  Fixed · Fixed: 6.4.2-3+deb13u2
  usn · python-tornado · debian · 13
- 6.4.2-3+deb13u2 · amd64 · trixie-security
  Fixed · Fixed: 6.4.2-3+deb13u2
  usn · python-tornado · debian · 13
- 6.4.2-3+deb13u2 · arm64 · trixie-security
  Fixed · Fixed: 6.4.2-3+deb13u2
  usn · python-tornado · debian · 13
[python-tornado-doc]Unknown
Source package: [python-tornado]
Details (4)
- 6.4.2-3+deb13u2 · all · trixie
  Fixed · Fixed: 6.4.2-3+deb13u2
  usn · python-tornado · debian · 13
- 6.4.2-3+deb13u2 · all · trixie
  Fixed · Fixed: 6.4.2-3+deb13u2
  usn · python-tornado · debian · 13
- 6.4.2-3+deb13u2 · all · trixie-security
  Fixed · Fixed: 6.4.2-3+deb13u2
  usn · python-tornado · debian · 13
- 6.4.2-3+deb13u2 · all · trixie-security
  Fixed · Fixed: 6.4.2-3+deb13u2
  usn · python-tornado · debian · 13

Observed: Oct 27, 2026, 10:47:34 AM UTC

References

[CERT-Bund public advisories] · [Debian Security Tracker] · [FIRST EPSS] · [GitHub Advisory Database] · [National Vulnerability Database (NVD)] · [OSV Package Vulnerability Database] · [Red Hat security advisories and VEX] · [SUSE security advisories and VEX] · [Ubuntu Security Notices (USN)]