Tornado: Event loop blocking and excess memory use from chunked bodies with many small chunks

{
  "id": "d6d9d30d7f3c671bd73a321f8627de916f45f56fb7a1989849ec82cd882680d2",
  "url": "https://www.cve.org/CVERecord?id=CVE-2026-115927",
  "method": "structured",
  "payload": {
    "kind": "advisory",
    "title": "Tornado: Event loop blocking and excess memory use from chunked bodies with many small chunks",
    "summary": "Tornado is a Python web framework and asynchronous networking library. Prior to 6.6.0, Tornado decodes HTTP/1.1 chunked transfer encoding by processing body data that has already arrived without yielding to the event loop. A remote unauthenticated peer can send millions of one-byte chunks to monopolize the process event loop and stall every other connection served by that process, while lowering max_body_size only limits the duration of each request. For handlers that do not use @stream_request_body, retaining each chunk as a separate object can consume roughly twenty times the received body size, and SimpleAsyncHTTPClient has the same event-loop behavior when reading a response from a malicious server. This issue is fixed in version 6.6.0.",
    "evidence": "cve:CVE-2026-115927",
    "products": [
      {
        "name": {
          "value": "tornado",
          "evidence": "/containers/cna/affected/0/product"
        },
        "prerequisites": [],
        "fixed_versions": [],
        "affected_versions": []
      }
    ],
    "severity": "medium",
    "structured": {
      "id": "CVE-2026-115927",
      "aliases": [
        "CVE-2026-115927"
      ],
      "metrics": [
        {
          "cvssV3_1": {
            "scope": "UNCHANGED",
            "version": "3.1",
            "baseScore": 5.3,
            "attackVector": "NETWORK",
            "baseSeverity": "MEDIUM",
            "vectorString": "CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:L",
            "integrityImpact": "NONE",
            "userInteraction": "NONE",
            "attackComplexity": "LOW",
            "availabilityImpact": "LOW",
            "privilegesRequired": "NONE",
            "confidentialityImpact": "NONE"
          }
        }
      ],
      "affected": [
        {
          "vendor": "tornadoweb",
          "product": "tornado",
          "versions": [
            {
              "status": "affected",
              "version": "< 6.6.0"
            }
          ]
        }
      ],
      "modified": "2026-10-27T14:18:44.227Z",
      "provider": "cve",
      "references": [
        "https://github.com/tornadoweb/tornado/security/advisories/GHSA-r4j5-9xpp-3985",
        "https://github.com/tornadoweb/tornado/pull/3773",
        "https://github.com/tornadoweb/tornado/commit/ceab33581489751a66fba8566ad6d5960d4b01c8",
        "https://github.com/tornadoweb/tornado/releases/tag/v6.6.0"
      ],
      "provider_metadata": {
        "adp": [
          {
            "title": "CISA ADP Vulnrichment",
            "metrics": [
              {
                "other": {
                  "type": "ssvc",
                  "content": {
                    "id": "CVE-2026-115927",
                    "role": "CISA Coordinator",
                    "options": [
                      {
                        "Exploitation": "none"
                      },
                      {
                        "Automatable": "yes"
                      },
                      {
                        "Technical Impact": "partial"
                      }
                    ],
                    "version": "2.0.3",
                    "timestamp": "2026-10-27T13:45:56.157686Z"
                  }
                }
              }
            ],
            "providerMetadata": {
              "orgId": "134c704f-9b21-4f2e-91b3-4a467353bcc0",
              "shortName": "CISA-ADP",
              "dateUpdated": "2026-10-27T14:18:44.227Z"
            }
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        ],
        "cna": {
          "orgId": "a0819718-46f1-4df5-94e2-005712e83aaa",
          "shortName": "GitHub_M",
          "dateUpdated": "2026-10-26T19:37:40.584Z"
        }
      }
    },
    "related_cves": [
      {
        "value": "CVE-2026-115927",
        "evidence": "/cveMetadata/cveId"
      }
    ],
    "security_relevant": true,
    "severity_evidence": "/containers/cna/metrics"
  },
  "source_id": "core-cve",
  "document_id": 392639,
  "published_at": "2026-10-26T19:37:40.584+00:00"
}