{
  "cveId": "CVE-2026-26209",
  "url": "https://patchblox.com/security/cve/CVE-2026-26209",
  "summary": "CVE-2026-26209 is fixed in 2 products on 1 platform, first by DEBIAN-CVE-2026-26209, released March 23, 2026. It is not reported as exploited. Patch Radar priority: High.",
  "title": "cbor2: cbor2 provides encoding and decoding for the Concise Binary Object Representation (CBOR) serialization format",
  "description": "cbor2 provides encoding and decoding for the Concise Binary Object Representation (CBOR) serialization format. Versions prior to 5.9.0 are vulnerable to a Denial of Service (DoS) attack caused by uncontrolled recursion when decoding deeply nested CBOR structures. This vulnerability affects both the pure Python implementation and the C extension \u0060_cbor2\u0060. The C extension relies on Python\u0027s internal recursion limits \u0060Py_EnterRecursiveCall\u0060 rather than a data-driven depth limit, meaning it still raises \u0060RecursionError\u0060 and crashes the worker process when the limit is hit. While the library handles moderate nesting levels, it lacks a hard depth limit. An attacker can supply a crafted CBOR payload containing approximately 100,000 nested arrays \u00600x81\u0060. When \u0060cbor2.loads()\u0060 attempts to parse this, it hits the Python interpreter\u0027s maximum recursion depth or exhausts the stack, causing the process to crash with a \u0060RecursionError\u0060. Because the library does not enforce its own limits, it allows an external attacker to exhaust the host application\u0027s stack resource. In many web application servers (e.g., Gunicorn, Uvicorn) or task queues (Celery), an unhandled \u0060RecursionError\u0060 terminates the worker process immediately. By sending a stream of these small (\u003C100KB) malicious packets, an attacker can repeatedly crash worker processes, resulting in a complete Denial of Service for the application. Version 5.9.0 patches the issue.",
  "published": "2026-03-23T19:16:39Z",
  "severity": "high",
  "cvss": 7.5,
  "cvssVector": "CVSS:3.0/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:H",
  "epss": 0.00397,
  "epssPercentile": 0.3417,
  "priority": "High",
  "priorityTier": 3,
  "exploited": false,
  "vendorExploited": false,
  "disclosed": false,
  "fixes": [
    {
      "platform": "linux",
      "product": "cbor2",
      "release": "Debian 14",
      "fixedVersion": "5.9.0-1",
      "fix": "DEBIAN-CVE-2026-26209",
      "url": "https://patchblox.com/security/fix/linux/debian-cve-2026-26209",
      "released": "2026-03-23T19:16:39Z"
    },
    {
      "platform": "linux",
      "product": "python-cbor2",
      "release": "opensuse-leap 16.0",
      "fixedVersion": "5.6.5-160000.4.1",
      "fix": "OPENSUSE-SU-2026:20468-1",
      "url": "https://patchblox.com/security/fix/linux/opensuse-su-2026-20468-1",
      "released": "2026-04-07T11:57:38Z"
    },
    {
      "platform": "linux",
      "product": "python-cbor2",
      "release": "sles 16.0",
      "fixedVersion": "5.6.5-160000.4.1",
      "fix": "SUSE-SU-2026:21139-1",
      "url": "https://patchblox.com/security/fix/linux/suse-su-2026-21139-1",
      "released": "2026-04-07T11:57:32Z"
    }
  ],
  "noFixYet": [],
  "dataAsOf": "2026-11-09T01:18:40Z",
  "attribution": {
    "text": "Data: Patchblox Patch Radar",
    "url": "https://patchblox.com/security/patch-radar",
    "terms": "https://patchblox.com/security/patch-radar/use-the-data"
  }
}