CVE-2026-49855 (GCVE-0-2026-49855)

Vulnerability from cvelistv5 – Published: 2026-07-14 20:45 – Updated: 2026-07-14 20:45
VLAI
Title
tornado AsyncHTTPClient accumulates decompressed chunks without size limit (gzip bomb)
Summary
Tornado is a Python web framework and asynchronous networking library. Prior to 6.5.6, Tornado gzip decompression routines processed limited-size chunks but did not enforce an overall limit on accumulated decompressed chunks, allowing a malicious server accessed by SimpleAsyncHTTPClient or an HTTPServer configured with decompress_request=True to consume effectively unlimited memory. This issue is fixed in version 6.5.6.
Severity
7.5 (High)
CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:H
CWE
  • CWE-409 - Improper Handling of Highly Compressed Data (Data Amplification)
Assigner
References
Impacted products
Vendor Product Version
tornadoweb tornado Affected: < 6.5.6
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{
  "containers": {
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      "affected": [
        {
          "product": "tornado",
          "vendor": "tornadoweb",
          "versions": [
            {
              "status": "affected",
              "version": "\u003c 6.5.6"
            }
          ]
        }
      ],
      "descriptions": [
        {
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          "value": "Tornado is a Python web framework and asynchronous networking library. Prior to 6.5.6, Tornado gzip decompression routines processed limited-size chunks but did not enforce an overall limit on accumulated decompressed chunks, allowing a malicious server accessed by SimpleAsyncHTTPClient or an HTTPServer configured with decompress_request=True to consume effectively unlimited memory. This issue is fixed in version 6.5.6."
        }
      ],
      "metrics": [
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          "cvssV3_1": {
            "attackComplexity": "LOW",
            "attackVector": "NETWORK",
            "availabilityImpact": "HIGH",
            "baseScore": 7.5,
            "baseSeverity": "HIGH",
            "confidentialityImpact": "NONE",
            "integrityImpact": "NONE",
            "privilegesRequired": "NONE",
            "scope": "UNCHANGED",
            "userInteraction": "NONE",
            "vectorString": "CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:H",
            "version": "3.1"
          }
        }
      ],
      "problemTypes": [
        {
          "descriptions": [
            {
              "cweId": "CWE-409",
              "description": "CWE-409: Improper Handling of Highly Compressed Data (Data Amplification)",
              "lang": "en",
              "type": "CWE"
            }
          ]
        }
      ],
      "providerMetadata": {
        "dateUpdated": "2026-07-14T20:45:02.982Z",
        "orgId": "a0819718-46f1-4df5-94e2-005712e83aaa",
        "shortName": "GitHub_M"
      },
      "references": [
        {
          "name": "https://github.com/tornadoweb/tornado/security/advisories/GHSA-mgf9-4vpg-hj56",
          "tags": [
            "x_refsource_CONFIRM"
          ],
          "url": "https://github.com/tornadoweb/tornado/security/advisories/GHSA-mgf9-4vpg-hj56"
        },
        {
          "name": "https://github.com/tornadoweb/tornado/pull/3626",
          "tags": [
            "x_refsource_MISC"
          ],
          "url": "https://github.com/tornadoweb/tornado/pull/3626"
        },
        {
          "name": "https://github.com/tornadoweb/tornado/commit/ff808b33adc52d89a549376a5e3628e92abbc8ff",
          "tags": [
            "x_refsource_MISC"
          ],
          "url": "https://github.com/tornadoweb/tornado/commit/ff808b33adc52d89a549376a5e3628e92abbc8ff"
        }
      ],
      "source": {
        "advisory": "GHSA-mgf9-4vpg-hj56",
        "discovery": "UNKNOWN"
      },
      "title": "tornado AsyncHTTPClient accumulates decompressed chunks without size limit (gzip bomb)"
    }
  },
  "cveMetadata": {
    "assignerOrgId": "a0819718-46f1-4df5-94e2-005712e83aaa",
    "assignerShortName": "GitHub_M",
    "cveId": "CVE-2026-49855",
    "datePublished": "2026-07-14T20:45:02.982Z",
    "dateReserved": "2026-06-01T22:03:19.640Z",
    "dateUpdated": "2026-07-14T20:45:02.982Z",
    "state": "PUBLISHED"
  },
  "dataType": "CVE_RECORD",
  "dataVersion": "5.2",
  "vulnerability-lookup:meta": {
    "epss": {
      "cve": "CVE-2026-49855",
      "date": "2026-07-15",
      "epss": "0.00691",
      "percentile": "0.48654"
    },
    "nvd": "{\"cve\":{\"id\":\"CVE-2026-49855\",\"sourceIdentifier\":\"security-advisories@github.com\",\"published\":\"2026-07-14T21:17:02.437\",\"lastModified\":\"2026-07-15T19:50:11.367\",\"vulnStatus\":\"Deferred\",\"cveTags\":[],\"descriptions\":[{\"lang\":\"en\",\"value\":\"Tornado is a Python web framework and asynchronous networking library. Prior to 6.5.6, Tornado gzip decompression routines processed limited-size chunks but did not enforce an overall limit on accumulated decompressed chunks, allowing a malicious server accessed by SimpleAsyncHTTPClient or an HTTPServer configured with decompress_request=True to consume effectively unlimited memory. This issue is fixed in version 6.5.6.\"}],\"affected\":[{\"source\":\"security-advisories@github.com\",\"affectedData\":[{\"vendor\":\"tornadoweb\",\"product\":\"tornado\",\"versions\":[{\"version\":\"\u003c 6.5.6\",\"status\":\"affected\"}]}]}],\"metrics\":{\"cvssMetricV31\":[{\"source\":\"security-advisories@github.com\",\"type\":\"Secondary\",\"cvssData\":{\"version\":\"3.1\",\"vectorString\":\"CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:H\",\"baseScore\":7.5,\"baseSeverity\":\"HIGH\",\"attackVector\":\"NETWORK\",\"attackComplexity\":\"LOW\",\"privilegesRequired\":\"NONE\",\"userInteraction\":\"NONE\",\"scope\":\"UNCHANGED\",\"confidentialityImpact\":\"NONE\",\"integrityImpact\":\"NONE\",\"availabilityImpact\":\"HIGH\"},\"exploitabilityScore\":3.9,\"impactScore\":3.6}]},\"weaknesses\":[{\"source\":\"security-advisories@github.com\",\"type\":\"Primary\",\"description\":[{\"lang\":\"en\",\"value\":\"CWE-409\"}]}],\"references\":[{\"url\":\"https://github.com/tornadoweb/tornado/commit/ff808b33adc52d89a549376a5e3628e92abbc8ff\",\"source\":\"security-advisories@github.com\"},{\"url\":\"https://github.com/tornadoweb/tornado/pull/3626\",\"source\":\"security-advisories@github.com\"},{\"url\":\"https://github.com/tornadoweb/tornado/security/advisories/GHSA-mgf9-4vpg-hj56\",\"source\":\"security-advisories@github.com\"}]}}"
  }
}



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