CVE-2023-29159: Starlette Path Traversal Vulnerability

{
  "schema_version" : "1.4.0",
  "id" : "GHSA-v5gw-mw7f-84px",
  "modified" : "2024-10-28T14:29:32Z",
  "published" : "2023-05-17T03:49:14Z",
  "aliases" : [ "CVE-2023-29159" ],
  "summary" : "Starlette has Path Traversal vulnerability in StaticFiles",
  "details" : "### Summary\nWhen using `StaticFiles`, if there's a file or directory that starts with the same name as the `StaticFiles` directory, that file or directory is also exposed via `StaticFiles` which is a path traversal vulnerability.\n\n### Details\nThe root cause of this issue is the usage of `os.path.commonprefix()`:\nhttps://github.com/encode/starlette/blob/4bab981d9e870f6cee1bd4cd59b87ddaf355b2dc/starlette/staticfiles.py#L172-L174\n\nAs stated in the Python documentation (https://docs.python.org/3/library/os.path.html#os.path.commonprefix) this function returns the longest prefix common to paths.\n\nWhen passing a path like `/static/../static1.txt`, `os.path.commonprefix([full_path, directory])` returns `./static` which is the common part of `./static1.txt` and `./static`, It refers to `/static/../static1.txt` because it is considered in the staticfiles directory. As a result, it becomes possible to view files that should not be open to the public.\n\nThe solution is to use `os.path.commonpath` as the Python documentation explains that `os.path.commonprefix` works a character at a time, it does not treat the arguments as paths.\n\n### PoC\nIn order to reproduce the issue, you need to create the following structure:\n\n```\n├── static\n│   ├── index.html\n├── static_disallow\n│   ├── index.html\n└── static1.txt\n```\n\nAnd run the `Starlette` app with:\n\n```py\nimport uvicorn\nfrom starlette.applications import Starlette\nfrom starlette.routing import Mount\nfrom starlette.staticfiles import StaticFiles\n\n\nroutes = [\n    Mount(\"/static\", app=StaticFiles(directory=\"static\", html=True), name=\"static\"),\n]\n\napp = Starlette(routes=routes)\n\n\nif __name__ == \"__main__\":\n    uvicorn.run(app, host=\"0.0.0.0\", port=8000)\n```\n\nAnd running the commands:\n\n```shell\ncurl --path-as-is 'localhost:8000/static/../static_disallow/'\ncurl --path-as-is 'localhost:8000/static/../static1.txt'\n```\nThe `static1.txt` and the directory `static_disallow` are exposed.\n\n### Impact\nConfidentiality is breached: An attacker may obtain files that should not be open to the public.\n\n### Credits\nSecurity researcher **Masashi Yamane of LAC Co., Ltd** reported this vulnerability to **JPCERT/CC Vulnerability Coordination Group** and they contacted us to coordinate a patch for the security issue.\n",
  "severity" : [ {
    "type" : "CVSS_V3",
    "score" : "CVSS:3.1/AV:N/AC:H/PR:N/UI:N/S:U/C:L/I:N/A:N"
  }, {
    "type" : "CVSS_V4",
    "score" : "CVSS:4.0/AV:N/AC:L/AT:P/PR:N/UI:N/VC:L/VI:N/VA:N/SC:N/SI:N/SA:N"
  } ],
  "affected" : [ {
    "package" : {
      "ecosystem" : "PyPI",
      "name" : "starlette"
    },
    "ranges" : [ {
      "type" : "ECOSYSTEM",
      "events" : [ {
        "introduced" : "0.13.5"
      }, {
        "fixed" : "0.27.0"
      } ]
    } ]
  } ],
  "references" : [ {
    "type" : "WEB",
    "url" : "https://github.com/encode/starlette/security/advisories/GHSA-v5gw-mw7f-84px"
  }, {
    "type" : "ADVISORY",
    "url" : "https://nvd.nist.gov/vuln/detail/CVE-2023-29159"
  }, {
    "type" : "WEB",
    "url" : "https://github.com/encode/starlette/commit/1797de464124b090f10cf570441e8292936d63e3"
  }, {
    "type" : "PACKAGE",
    "url" : "https://github.com/encode/starlette"
  }, {
    "type" : "WEB",
    "url" : "https://github.com/encode/starlette/blob/4bab981d9e870f6cee1bd4cd59b87ddaf355b2dc/starlette/staticfiles.py#L172-L174"
  }, {
    "type" : "WEB",
    "url" : "https://github.com/encode/starlette/releases/tag/0.27.0"
  }, {
    "type" : "WEB",
    "url" : "https://github.com/pypa/advisory-database/tree/main/vulns/starlette/PYSEC-2023-83.yaml"
  }, {
    "type" : "WEB",
    "url" : "https://jvn.jp/en/jp/JVN95981715"
  } ],
  "database_specific" : {
    "cwe_ids" : [ "CWE-22" ],
    "severity" : "MODERATE",
    "github_reviewed" : true,
    "github_reviewed_at" : "2023-05-17T03:49:14Z",
    "nvd_published_at" : null
  }
}