CVE-2024-47874

Starlette treats multipart/form-data parts without a filename as text form fields and buffers those in byte strings with no size limit. This allows an attacker to upload arbitrary large form fields and 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, or the OS terminates the server process with an OOM error. Uploading multiple such requests in parallel may be enough to render a service practically unusable, even if reasonable request size limits are enforced by a reverse proxy in front of Starlette.

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'

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

The application allocates resources such as memory, threads, or file descriptors based on untrusted input without enforcing a cap. Typical impact: resource exhaustion leading to denial of service.

Kodem intelligence

1. What is CVE-2024-47874? CVE-2024-47874 is a high-severity allocation of resources without limits or throttling vulnerability in starlette (pip), affecting versions < 0.40.0. It is fixed in 0.40.0. The application allocates resources such as memory, threads, or file descriptors based on untrusted input without enforcing a cap.
2. Which versions of starlette are affected by CVE-2024-47874? starlette (pip) versions < 0.40.0 is affected.
3. Is there a fix for CVE-2024-47874? Yes. CVE-2024-47874 is fixed in 0.40.0. Upgrade to this version or later.
4. Is CVE-2024-47874 exploitable, and should I be worried? Whether CVE-2024-47874 is exploitable in your environment depends on whether the vulnerable code is present and reachable. A CVSS score is a worst-case rating; it does not account for your specific deployment, configuration, or usage patterns. Kodem, an Intelligent Application Security platform, uses runtime intelligence to show which vulnerabilities actually execute in production, so you can focus on the ones that represent real risk. Get a demo
5. What actually determines whether CVE-2024-47874 is exploitable, and how bad it is? Exploitability and impact are not fixed properties of a CVE. They depend on runtime truth: whether the vulnerable code is present, reachable, and actually executes in your application. A high CVSS score on a dependency that never runs is not the same as real risk. Kodem, an Intelligent Application Security platform, uses runtime intelligence to reveal which vulnerabilities actually execute in production, so teams prioritize the ones that genuinely matter.
6. How do I fix CVE-2024-47874? Upgrade starlette to 0.40.0 or later.