ghsa-v5gw-mw7f-84px
Vulnerability from github
Summary
When 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.
Details
The root cause of this issue is the usage of os.path.commonprefix():
https://github.com/encode/starlette/blob/4bab981d9e870f6cee1bd4cd59b87ddaf355b2dc/starlette/staticfiles.py#L172-L174
As 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.
When 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.
The 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.
PoC
In order to reproduce the issue, you need to create the following structure:
├── static
│ ├── index.html
├── static_disallow
│ ├── index.html
└── static1.txt
And run the Starlette app with:
```py import uvicorn from starlette.applications import Starlette from starlette.routing import Mount from starlette.staticfiles import StaticFiles
routes = [ Mount("/static", app=StaticFiles(directory="static", html=True), name="static"), ]
app = Starlette(routes=routes)
if name == "main": uvicorn.run(app, host="0.0.0.0", port=8000) ```
And running the commands:
shell
curl --path-as-is 'localhost:8000/static/../static_disallow/'
curl --path-as-is 'localhost:8000/static/../static1.txt'
The static1.txt and the directory static_disallow are exposed.
Impact
Confidentiality is breached: An attacker may obtain files that should not be open to the public.
Credits
Security 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.
{
"affected": [
{
"ecosystem_specific": {
"affected_functions": [
"starlette.staticfiles.StaticFiles.lookup_path"
]
},
"package": {
"ecosystem": "PyPI",
"name": "starlette"
},
"ranges": [
{
"events": [
{
"introduced": "0.13.5"
},
{
"fixed": "0.27.0"
}
],
"type": "ECOSYSTEM"
}
]
}
],
"aliases": [
"CVE-2023-29159"
],
"database_specific": {
"cwe_ids": [
"CWE-22"
],
"github_reviewed": true,
"github_reviewed_at": "2023-05-17T03:49:14Z",
"nvd_published_at": null,
"severity": "LOW"
},
"details": "### Summary\nWhen using `StaticFiles`, if there\u0027s 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\u251c\u2500\u2500 static\n\u2502 \u251c\u2500\u2500 index.html\n\u251c\u2500\u2500 static_disallow\n\u2502 \u251c\u2500\u2500 index.html\n\u2514\u2500\u2500 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 \u0027localhost:8000/static/../static_disallow/\u0027\ncurl --path-as-is \u0027localhost:8000/static/../static1.txt\u0027\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",
"id": "GHSA-v5gw-mw7f-84px",
"modified": "2023-06-12T16:47:36Z",
"published": "2023-05-17T03:49:14Z",
"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"
}
],
"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": "Starlette has Path Traversal vulnerability in StaticFiles"
}