Vulnerability-Lookup

CVE-2026-82397 (GCVE-0-2026-82397)

Vulnerability from cvelistv5 – Published: 2026-08-31 21:28 – Updated: 2026-09-02 17:39

Title

Tornado: Urlencoded body parsing omits max_num_fields, so one request can stall the event loop

Summary

Tornado is a Python web framework and asynchronous networking library. Prior to 6.5.8, Tornado parses application/x-www-form-urlencoded request bodies with urllib.parse.parse_qs in tornado/escape.py without passing max_num_fields. RequestHandler._execute in tornado/web.py parses the body before handler dispatch through HTTPServerRequest._parse_body and parse_body_arguments in tornado/httputil.py, so an unauthenticated request body containing millions of separator-delimited fields can synchronously stall the single-threaded event loop and delay every connection. The body is bounded only by max_buffer_size, which defaults to 104857600 bytes. This issue is fixed in version 6.5.8.

Severity

7.5 (High)


                        
                          CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:H

SSVC

Exploitation: none Automatable: yes Technical Impact: partial

CISA Coordinator · CISA-ADP (v2.0.3)

Decision recorded 2026-09-02 17:39 UTC

CWE

CWE-400 - Uncontrolled Resource Consumption
CWE-1284 - Improper Validation of Specified Quantity in Input

Assigner

GitHub_M mitre root

References

4 references

URL	Tags
https://github.com/tornadoweb/tornado/security/ad…	x_refsource_CONFIRM
https://github.com/tornadoweb/tornado/pull/3704	x_refsource_MISC
https://github.com/tornadoweb/tornado/commit/8d63…	x_refsource_MISC
https://github.com/tornadoweb/tornado/releases/ta…	x_refsource_MISC

Impacted products

1 product

Vendor	Product	Version	CPE status
tornadoweb	tornado	Affected: < 6.5.8	guessed

Show details on NVD website

JSON

To clipboard

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                "id": "CVE-2026-82397",
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FKIE_CVE-2026-82397

Vulnerability from fkie_nvd - Published: 2026-08-31 22:17 - Updated: 2026-09-02 18:21

Severity

7.5 (High) - CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:H

Summary

References

	URL	Tags
	security-advisories@github.com	https://github.com/tornadoweb/tornado/commit/8d6363ed7b69d5f0da806efe34d256627a2191de
	security-advisories@github.com	https://github.com/tornadoweb/tornado/pull/3704
	security-advisories@github.com	https://github.com/tornadoweb/tornado/releases/tag/v6.5.8
	security-advisories@github.com	https://github.com/tornadoweb/tornado/security/advisories/GHSA-mpf4-983q-p7j4

Impacted products

	Vendor	Product	Version

JSON

To clipboard

{
  "affected": [
    {
      "affectedData": [
        {
          "product": "tornado",
          "vendor": "tornadoweb",
          "versions": [
            {
              "status": "affected",
              "version": "\u003c 6.5.8"
            }
          ]
        }
      ],
      "source": "security-advisories@github.com"
    }
  ],
  "cveTags": [],
  "descriptions": [
    {
      "lang": "en",
      "value": "Tornado is a Python web framework and asynchronous networking library. Prior to 6.5.8, Tornado parses application/x-www-form-urlencoded request bodies with urllib.parse.parse_qs in tornado/escape.py without passing max_num_fields. RequestHandler._execute in tornado/web.py parses the body before handler dispatch through HTTPServerRequest._parse_body and parse_body_arguments in tornado/httputil.py, so an unauthenticated request body containing millions of separator-delimited fields can synchronously stall the single-threaded event loop and delay every connection. The body is bounded only by max_buffer_size, which defaults to 104857600 bytes. This issue is fixed in version 6.5.8."
    }
  ],
  "id": "CVE-2026-82397",
  "lastModified": "2026-09-02T18:21:27.330",
  "metrics": {
    "cvssMetricV31": [
      {
        "cvssData": {
          "attackComplexity": "LOW",
          "attackVector": "NETWORK",
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          "baseScore": 7.5,
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          "confidentialityImpact": "NONE",
          "integrityImpact": "NONE",
          "privilegesRequired": "NONE",
          "scope": "UNCHANGED",
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  "references": [
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      "url": "https://github.com/tornadoweb/tornado/commit/8d6363ed7b69d5f0da806efe34d256627a2191de"
    },
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GHSA-MPF4-983Q-P7J4

Vulnerability from github – Published: 2026-09-02 14:38 – Updated: 2026-09-02 14:38

Summary

Tornado: Urlencoded body parsing omits max_num_fields, so one request can stall the event loop

Details

Summary

Tornado parses application/x-www-form-urlencoded bodies with urllib.parse.parse_qs and does not pass max_num_fields. A body made almost entirely of separators produces tens of millions of fields, and the parse happens on the event loop before the handler runs, so a single request stalls the whole server.

Where it is

tornado/escape.py, at HEAD e530031405e2154654dedc4c84d5656b557ea310:

result = urllib.parse.parse_qs(
    qs, keep_blank_values, strict_parsing, encoding="latin1", errors="strict"
)

max_num_fields is the parameter CPython added for exactly this, and it is absent.

The path to it is entirely server-side and pre-dispatch. RequestHandler._execute parses the body at tornado/web.py:1821, which reaches HTTPServerRequest._parse_body at tornado/httputil.py:636, and the urlencoded branch of parse_body_arguments calls parse_qs_bytes at tornado/httputil.py:1030.

The size that reaches it is bounded only by the body cap, which defaults to the stream's max_buffer_size of 104857600 at tornado/iostream.py:239, applied as the request body default at tornado/http1connection.py:136-140. A 100 MB body of separators is around fifty million fields.

Impact

Denial of service against the whole process, not one request. Tornado is single-threaded and the parse is synchronous on the event loop, so every other connection waits. No authentication is needed if any route accepts a form post, which is the normal case.

Suggested fix

Pass a bound:

result = urllib.parse.parse_qs(
    qs, keep_blank_values, strict_parsing, encoding="latin1", errors="strict",
    max_num_fields=max_num_fields,
)

with a conservative default and a way for applications to raise it. CPython raises ValueError when the limit is exceeded, which maps cleanly onto a 400.

Lowering the default body cap for urlencoded specifically would help too, since 100 MB of form fields is not a shape any real client sends.

Why I do not think this is a duplicate

The published tornado advisories cover out-of-bounds access in the C extension, unbounded accumulation of decompressed chunks in AsyncHTTPClient, the Authorization header surviving cross-origin redirects, credential leakage on curl handle reuse, and cookie attribute validation. The decompression one is the nearest in spirit and is on the client side; this is the server parsing a request body. The call is unchanged at HEAD.

Severity

7.5 (High)


                  
                    CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:H

Show details on source website

JSON

To clipboard

{
  "affected": [
    {
      "database_specific": {
        "last_known_affected_version_range": "\u003c= 6.5.7"
      },
      "package": {
        "ecosystem": "PyPI",
        "name": "tornado"
      },
      "ranges": [
        {
          "events": [
            {
              "introduced": "0"
            },
            {
              "fixed": "6.5.8"
            }
          ],
          "type": "ECOSYSTEM"
        }
      ]
    }
  ],
  "aliases": [
    "CVE-2026-82397"
  ],
  "database_specific": {
    "cwe_ids": [
      "CWE-1284",
      "CWE-400"
    ],
    "github_reviewed": true,
    "github_reviewed_at": "2026-09-02T14:38:43Z",
    "nvd_published_at": "2026-08-31T22:17:22Z",
    "severity": "HIGH"
  },
  "details": "## Summary\n\nTornado parses `application/x-www-form-urlencoded` bodies with `urllib.parse.parse_qs` and does not pass `max_num_fields`. A body made almost entirely of separators produces tens of millions of fields, and the parse happens on the event loop before the handler runs, so a single request stalls the whole server.\n\n## Where it is\n\n`tornado/escape.py`, at HEAD `e530031405e2154654dedc4c84d5656b557ea310`:\n\n```python\nresult = urllib.parse.parse_qs(\n    qs, keep_blank_values, strict_parsing, encoding=\"latin1\", errors=\"strict\"\n)\n```\n\n`max_num_fields` is the parameter CPython added for exactly this, and it is absent.\n\nThe path to it is entirely server-side and pre-dispatch. `RequestHandler._execute` parses the body at `tornado/web.py:1821`, which reaches `HTTPServerRequest._parse_body` at `tornado/httputil.py:636`, and the urlencoded branch of `parse_body_arguments` calls `parse_qs_bytes` at `tornado/httputil.py:1030`.\n\nThe size that reaches it is bounded only by the body cap, which defaults to the stream\u0027s `max_buffer_size` of 104857600 at `tornado/iostream.py:239`, applied as the request body default at `tornado/http1connection.py:136-140`. A 100 MB body of separators is around fifty million fields.\n\n## Impact\n\nDenial of service against the whole process, not one request. Tornado is single-threaded and the parse is synchronous on the event loop, so every other connection waits. No authentication is needed if any route accepts a form post, which is the normal case.\n\n## Suggested fix\n\nPass a bound:\n\n```python\nresult = urllib.parse.parse_qs(\n    qs, keep_blank_values, strict_parsing, encoding=\"latin1\", errors=\"strict\",\n    max_num_fields=max_num_fields,\n)\n```\n\nwith a conservative default and a way for applications to raise it. CPython raises `ValueError` when the limit is exceeded, which maps cleanly onto a 400.\n\nLowering the default body cap for urlencoded specifically would help too, since 100 MB of form fields is not a shape any real client sends.\n\n## Why I do not think this is a duplicate\n\nThe published tornado advisories cover out-of-bounds access in the C extension, unbounded accumulation of decompressed chunks in `AsyncHTTPClient`, the Authorization header surviving cross-origin redirects, credential leakage on curl handle reuse, and cookie attribute validation. The decompression one is the nearest in spirit and is on the client side; this is the server parsing a request body. The call is unchanged at HEAD.",
  "id": "GHSA-mpf4-983q-p7j4",
  "modified": "2026-09-02T14:38:43Z",
  "published": "2026-09-02T14:38:43Z",
  "references": [
    {
      "type": "WEB",
      "url": "https://github.com/tornadoweb/tornado/security/advisories/GHSA-mpf4-983q-p7j4"
    },
    {
      "type": "ADVISORY",
      "url": "https://nvd.nist.gov/vuln/detail/CVE-2026-82397"
    },
    {
      "type": "WEB",
      "url": "https://github.com/tornadoweb/tornado/pull/3704"
    },
    {
      "type": "WEB",
      "url": "https://github.com/tornadoweb/tornado/commit/8d6363ed7b69d5f0da806efe34d256627a2191de"
    },
    {
      "type": "PACKAGE",
      "url": "https://github.com/tornadoweb/tornado"
    },
    {
      "type": "WEB",
      "url": "https://github.com/tornadoweb/tornado/releases/tag/v6.5.8"
    }
  ],
  "schema_version": "1.4.0",
  "severity": [
    {
      "score": "CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:H",
      "type": "CVSS_V3"
    }
  ],
  "summary": " Tornado: Urlencoded body parsing omits max_num_fields, so one request can stall the event loop"
}

ubuntu-cve-2026-82397

Vulnerability from osv_ubuntu

Published

2026-08-31 22:17

Modified

2026-09-02 16:28

Summary

Details

Severity

7.5 (High)


                    
                      CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:H

N/A (UNKNOWN)


                    
                      medium

References

URL

Type

	https://ubuntu.com/security/CVE-2026-82397	REPORT
	https://www.cve.org/CVERecord?id=CVE-2026-82397	REPORT
	https://github.com/tornadoweb/tornado/security/ad…	REPORT
	https://github.com/tornadoweb/tornado/commit/8d63…	REPORT
	https://github.com/tornadoweb/tornado/pull/3704	REPORT
	https://github.com/tornadoweb/tornado/releases/ta…	REPORT

JSON

To clipboard

{
  "affected": [
    {
      "ecosystem_specific": {
        "binaries": [
          {
            "binary_name": "python-tornado",
            "binary_version": "4.2.1-1ubuntu3.1+esm3"
          },
          {
            "binary_name": "python3-tornado",
            "binary_version": "4.2.1-1ubuntu3.1+esm3"
          }
        ]
      },
      "package": {
        "ecosystem": "Ubuntu:Pro:16.04:LTS",
        "name": "python-tornado",
        "purl": "pkg:deb/ubuntu/python-tornado@4.2.1-1ubuntu3.1+esm3?arch=source\u0026distro=esm-infra/xenial"
      },
      "ranges": [
        {
          "events": [
            {
              "introduced": "0"
            }
          ],
          "type": "ECOSYSTEM"
        }
      ],
      "versions": [
        "4.2.1-1ubuntu2",
        "4.2.1-1ubuntu3",
        "4.2.1-1ubuntu3.1",
        "4.2.1-1ubuntu3.1+esm1",
        "4.2.1-1ubuntu3.1+esm2",
        "4.2.1-1ubuntu3.1+esm3"
      ]
    },
    {
      "ecosystem_specific": {
        "binaries": [
          {
            "binary_name": "python-tornado",
            "binary_version": "4.5.3-1ubuntu0.2+esm3"
          },
          {
            "binary_name": "python3-tornado",
            "binary_version": "4.5.3-1ubuntu0.2+esm3"
          }
        ]
      },
      "package": {
        "ecosystem": "Ubuntu:Pro:18.04:LTS",
        "name": "python-tornado",
        "purl": "pkg:deb/ubuntu/python-tornado@4.5.3-1ubuntu0.2+esm3?arch=source\u0026distro=esm-apps/bionic"
      },
      "ranges": [
        {
          "events": [
            {
              "introduced": "0"
            }
          ],
          "type": "ECOSYSTEM"
        }
      ],
      "versions": [
        "4.5.1-2.1~build2",
        "4.5.2-1",
        "4.5.3-1",
        "4.5.3-1ubuntu0.1",
        "4.5.3-1ubuntu0.2",
        "4.5.3-1ubuntu0.2+esm1",
        "4.5.3-1ubuntu0.2+esm2",
        "4.5.3-1ubuntu0.2+esm3"
      ]
    },
    {
      "ecosystem_specific": {
        "binaries": [
          {
            "binary_name": "python3-tornado",
            "binary_version": "6.0.3+really5.1.1-3ubuntu0.1~esm5"
          }
        ]
      },
      "package": {
        "ecosystem": "Ubuntu:Pro:20.04:LTS",
        "name": "python-tornado",
        "purl": "pkg:deb/ubuntu/python-tornado@6.0.3+really5.1.1-3ubuntu0.1~esm5?arch=source\u0026distro=esm-apps/focal"
      },
      "ranges": [
        {
          "events": [
            {
              "introduced": "0"
            }
          ],
          "type": "ECOSYSTEM"
        }
      ],
      "versions": [
        "5.1.1-4ubuntu1",
        "5.1.1-4ubuntu5",
        "6.0.3+really5.1.1-2",
        "6.0.3+really5.1.1-2build1",
        "6.0.3+really5.1.1-2build2",
        "6.0.3+really5.1.1-3",
        "6.0.3+really5.1.1-3ubuntu0.1~esm1",
        "6.0.3+really5.1.1-3ubuntu0.1~esm3",
        "6.0.3+really5.1.1-3ubuntu0.1~esm5"
      ]
    },
    {
      "ecosystem_specific": {
        "binaries": [
          {
            "binary_name": "python3-tornado",
            "binary_version": "6.1.0-3ubuntu0.1~esm5"
          }
        ]
      },
      "package": {
        "ecosystem": "Ubuntu:Pro:22.04:LTS",
        "name": "python-tornado",
        "purl": "pkg:deb/ubuntu/python-tornado@6.1.0-3ubuntu0.1~esm5?arch=source\u0026distro=esm-apps/jammy"
      },
      "ranges": [
        {
          "events": [
            {
              "introduced": "0"
            }
          ],
          "type": "ECOSYSTEM"
        }
      ],
      "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",
        "6.1.0-3ubuntu0.1~esm4",
        "6.1.0-3ubuntu0.1~esm5"
      ]
    },
    {
      "ecosystem_specific": {
        "binaries": [
          {
            "binary_name": "python3-tornado",
            "binary_version": "6.4.0-1ubuntu0.5"
          }
        ]
      },
      "package": {
        "ecosystem": "Ubuntu:24.04:LTS",
        "name": "python-tornado",
        "purl": "pkg:deb/ubuntu/python-tornado@6.4.0-1ubuntu0.5?arch=source\u0026distro=noble"
      },
      "ranges": [
        {
          "events": [
            {
              "introduced": "0"
            }
          ],
          "type": "ECOSYSTEM"
        }
      ],
      "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",
        "6.4.0-1ubuntu0.4",
        "6.4.0-1ubuntu0.5"
      ]
    },
    {
      "ecosystem_specific": {
        "binaries": [
          {
            "binary_name": "python3-tornado",
            "binary_version": "6.5.4-0.1ubuntu0.1"
          }
        ]
      },
      "package": {
        "ecosystem": "Ubuntu:26.04:LTS",
        "name": "python-tornado",
        "purl": "pkg:deb/ubuntu/python-tornado@6.5.4-0.1ubuntu0.1?arch=source\u0026distro=resolute"
      },
      "ranges": [
        {
          "events": [
            {
              "introduced": "0"
            }
          ],
          "type": "ECOSYSTEM"
        }
      ],
      "versions": [
        "6.4.2-3",
        "6.5.2-3",
        "6.5.4-0.1",
        "6.5.4-0.1ubuntu0.1"
      ]
    }
  ],
  "aliases": [],
  "details": "Tornado is a Python web framework and asynchronous networking library. Prior to 6.5.8, Tornado parses application/x-www-form-urlencoded request bodies with urllib.parse.parse_qs in tornado/escape.py without passing max_num_fields. RequestHandler._execute in tornado/web.py parses the body before handler dispatch through HTTPServerRequest._parse_body and parse_body_arguments in tornado/httputil.py, so an unauthenticated request body containing millions of separator-delimited fields can synchronously stall the single-threaded event loop and delay every connection. The body is bounded only by max_buffer_size, which defaults to 104857600 bytes. This issue is fixed in version 6.5.8.",
  "id": "UBUNTU-CVE-2026-82397",
  "modified": "2026-09-02T16:28:28Z",
  "published": "2026-08-31T22:17:00Z",
  "references": [
    {
      "type": "REPORT",
      "url": "https://ubuntu.com/security/CVE-2026-82397"
    },
    {
      "type": "REPORT",
      "url": "https://www.cve.org/CVERecord?id=CVE-2026-82397"
    },
    {
      "type": "REPORT",
      "url": "https://github.com/tornadoweb/tornado/security/advisories/GHSA-mpf4-983q-p7j4"
    },
    {
      "type": "REPORT",
      "url": "https://github.com/tornadoweb/tornado/commit/8d6363ed7b69d5f0da806efe34d256627a2191de"
    },
    {
      "type": "REPORT",
      "url": "https://github.com/tornadoweb/tornado/pull/3704"
    },
    {
      "type": "REPORT",
      "url": "https://github.com/tornadoweb/tornado/releases/tag/v6.5.8"
    }
  ],
  "related": [],
  "schema_version": "1.7.0",
  "severity": [
    {
      "score": "CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:H",
      "type": "CVSS_V3"
    },
    {
      "score": "medium",
      "type": "Ubuntu"
    }
  ],
  "upstream": [
    "CVE-2026-82397"
  ]
}

Sightings

Author	Source	Type	Date	Other

Nomenclature

Seen: The vulnerability was mentioned, discussed, or observed by the user.
Confirmed: The vulnerability has been validated from an analyst's perspective.
Published Proof of Concept: A public proof of concept is available for this vulnerability.
Exploited: The vulnerability was observed as exploited by the user who reported the sighting.
Patched: The vulnerability was observed as successfully patched by the user who reported the sighting.
Not exploited: The vulnerability was not observed as exploited by the user who reported the sighting.
Not confirmed: The user expressed doubt about the validity of the vulnerability.
Not patched: The vulnerability was not observed as successfully patched by the user who reported the sighting.

Detection rules are retrieved from Rulezet.

The MITRE ATT&CK techniques below are AI-generated suggestions, inferred from the description of the vulnerability by the CIRCL/vulnerability-attack-technique-classification-roberta-base model, served locally by ML-Gateway. They have not been verified by an analyst and are provided for guidance only.
The approach is described in our paper Mapping CVEs to MITRE ATT&CK Techniques: A Curated Gold-Set Classifier and the Limits of LLM-Assisted Label Expansion.

Action not permitted

CVE-2026-82397 (GCVE-0-2026-82397)

FKIE_CVE-2026-82397

GHSA-MPF4-983Q-P7J4

Summary

Where it is

Impact

Suggested fix

Why I do not think this is a duplicate

ubuntu-cve-2026-82397

Vulnerability from osv_ubuntu

Tags

Sightings

Nomenclature