GHSA-CX3H-4QPV-8HC9

Vulnerability from github – Published: 2026-06-12 18:30 – Updated: 2026-06-12 18:30
VLAI
Summary
Tornado has out-of-bounds memory access via C extension
Details

Summary

Tornado's optional native extension tornado.speedups implements websocket_mask without validating that the mask argument is exactly four bytes long. The C function reads four bytes from mask unconditionally, even when Python passes a shorter byte string. This can read beyond the provided buffer, exposing up to 3 bytes of uninitialized memory.

The behavior is reachable from Tornado's XSRF token decoder when xsrf_cookies=True and the native extension is active.

Mitigations

This bug is fixed in Tornado 6.5.6. Prior to upgrading to this version, setting the environment variable TORNADO_EXTENSION=0 will disable the vulnerable code (at the expense of reducing websocket performance).

Severity
3.7 (Low)
CVSS:3.1/AV:N/AC:H/PR:N/UI:N/S:U/C:L/I:N/A:N
Show details on source website
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{
  "affected": [
    {
      "package": {
        "ecosystem": "PyPI",
        "name": "tornado"
      },
      "ranges": [
        {
          "events": [
            {
              "introduced": "0"
            },
            {
              "fixed": "6.5.6"
            }
          ],
          "type": "ECOSYSTEM"
        }
      ]
    }
  ],
  "aliases": [
    "CVE-2026-49854"
  ],
  "database_specific": {
    "cwe_ids": [
      "CWE-126"
    ],
    "github_reviewed": true,
    "github_reviewed_at": "2026-06-12T18:30:19Z",
    "nvd_published_at": null,
    "severity": "LOW"
  },
  "details": "### Summary\n\nTornado\u0027s optional native extension `tornado.speedups` implements `websocket_mask` without validating that the `mask` argument is exactly four bytes long. The C function reads four bytes from `mask` unconditionally, even when Python passes a shorter byte string. This can read beyond the provided buffer, exposing up to 3 bytes of uninitialized memory.\n\nThe behavior is reachable from Tornado\u0027s XSRF token decoder when `xsrf_cookies=True` and the native extension is active. \n\n### Mitigations\n\nThis bug is fixed in Tornado 6.5.6. Prior to upgrading to this version, setting the environment variable TORNADO_EXTENSION=0 will disable the vulnerable code (at the expense of reducing websocket performance).",
  "id": "GHSA-cx3h-4qpv-8hc9",
  "modified": "2026-06-12T18:30:19Z",
  "published": "2026-06-12T18:30:19Z",
  "references": [
    {
      "type": "WEB",
      "url": "https://github.com/tornadoweb/tornado/security/advisories/GHSA-cx3h-4qpv-8hc9"
    },
    {
      "type": "PACKAGE",
      "url": "https://github.com/tornadoweb/tornado"
    },
    {
      "type": "WEB",
      "url": "https://github.com/tornadoweb/tornado/releases/tag/v6.5.6"
    }
  ],
  "schema_version": "1.4.0",
  "severity": [
    {
      "score": "CVSS:3.1/AV:N/AC:H/PR:N/UI:N/S:U/C:L/I:N/A:N",
      "type": "CVSS_V3"
    }
  ],
  "summary": "Tornado has out-of-bounds memory access via C extension"
}



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