{
  "affected": [
    {
      "package": {
        "ecosystem": "PyPI",
        "name": "tornado"
      },
      "ranges": [
        {
          "events": [
            {
              "introduced": "0"
            },
            {
              "fixed": "6.5.6"
            }
          ],
          "type": "ECOSYSTEM"
        }
      ]
    }
  ],
  "aliases": [
    "CVE-2026-49855"
  ],
  "database_specific": {
    "cwe_ids": [
      "CWE-409"
    ],
    "github_reviewed": true,
    "github_reviewed_at": "2026-06-15T20:19:28Z",
    "nvd_published_at": null,
    "severity": "HIGH"
  },
  "details": "Tornado\u0027s gzip decompression routines work in limited-size chunks, but have no overall limit for the total size of decompressed chunks that they will accumulate (There has always been a limit for the total *compressed* size). This allows a malicious server to consume effectively unlimited amounts of memory if it is accessed via SimpleAsyncHTTPClient in its default configuration. `HTTPServer` is not affected in its default configuration, but it is if `decompress_request=True` is set.\n\nThis bug is fixed in Tornado 6.5.6. `max_body_size` is now checked both for the compressed and cumulative decompressed size of the response.\n\nPrior to upgrading, this issue can be mitigated by setting `decompress_response=False` or using `CurlAsyncHTTPClient`.",
  "id": "GHSA-mgf9-4vpg-hj56",
  "modified": "2026-06-15T20:19:28Z",
  "published": "2026-06-15T20:19:28Z",
  "references": [
    {
      "type": "WEB",
      "url": "https://github.com/tornadoweb/tornado/security/advisories/GHSA-mgf9-4vpg-hj56"
    },
    {
      "type": "PACKAGE",
      "url": "https://github.com/tornadoweb/tornado"
    }
  ],
  "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 AsyncHTTPClient accumulates decompressed chunks without size limit (gzip bomb)"
}