chore(deps): update dependency starlette to ^0.27.0 [security]

[renovate]

This PR contains the following updates:

Package	Change	Age	Adoption	Passing	Confidence
starlette (changelog)	^0.26.1 -> ^0.27.0

GitHub Vulnerability Alerts

CVE-2023-29159

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:

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:

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.

---

Release Notes

encode/starlette

v0.27.0: Version 0.27.0

Compare Source

This release fixes a path traversal vulnerability in StaticFiles. You can view the full security advisory:
GHSA-v5gw-mw7f-84px

Added

• Minify JSON websocket data via send_json https://github.com/encode/starlette/pull/2128

Fixed

• Replace commonprefix by commonpath on StaticFiles 1797de4.
• Convert ImportErrors into ModuleNotFoundError #​2135.
• Correct the RuntimeError message content in websockets #​2141.

Full Changelog: encode/starlette@0.26.1...0.27.0

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