Allocation of Resources Without Limits or Throttling Affecting starlette package, versions [,0.40.0)


Severity

Recommended
0.0
high
0
10

CVSS assessment made by Snyk's Security Team

    Threat Intelligence

    Exploit Maturity
    Proof of concept
    EPSS
    0.04% (11th percentile)

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  • Snyk ID SNYK-PYTHON-STARLETTE-8186175
  • published 15 Oct 2024
  • disclosed 15 Oct 2024
  • credit Marcel Hellkamp

How to fix?

Upgrade starlette to version 0.40.0 or higher.

Overview

starlette is a The little ASGI library that shines.

Affected versions of this package are vulnerable to Allocation of Resources Without Limits or Throttling via multipart/form-data requests, due to treating parts without a filename as text form fields and buffering those in byte strings with no size limit.

An attacker could cause Starlette to both slow down significantly due to excessive memory allocations and copy operations, and also consume more and more memory until the server starts swapping and grinds to a halt by uploading arbitrary large form fields.

Note:

This vulnerability affects all applications built with Starlette (or FastAPI) accepting form requests.

PoC

from starlette.applications import Starlette
from starlette.routing import Route

async def poc(request):
    async with request.form():
        pass

app = Starlette(routes=[
    Route('/', poc, methods=["POST"]),
])
curl http://localhost:8000 -F 'big=</dev/urandom'

CVSS Scores

version 4.0
version 3.1
Expand this section

Snyk

Recommended
8.7 high
  • Attack Vector (AV)
    Network
  • Attack Complexity (AC)
    Low
  • Attack Requirements (AT)
    None
  • Privileges Required (PR)
    None
  • User Interaction (UI)
    None
  • Confidentiality (VC)
    None
  • Integrity (VI)
    None
  • Availability (VA)
    High
  • Confidentiality (SC)
    None
  • Integrity (SI)
    None
  • Availability (SA)
    None