CVE-2024-47874 — starlette
Fix: encode/starlette@fd038f3CVE-2024-47874 is a CWE-770 vulnerability in starlette. A fix is available for starlette — see the affected versions and patch details below.
Starlette Denial of service (DoS) via multipart/form-data
Exploitation Status
Proof-of-concept exploit code exists
- CISA’s SSVC triage found public proof-of-concept exploit code for this CVE, though no confirmed active exploitation.
- CISA assesses this as automatable — exploitation doesn’t require manual, per-target effort, which raises the odds of mass scanning and opportunistic attacks.
Exploitation and automatability from CISA’s SSVC triage for CVE-2024-47874.
EPSS Exploitation Probability
EPSS (Exploit Prediction Scoring System) is a daily probability model maintained by FIRST.org. It estimates the likelihood a CVE will be exploited in production environments within the next 30 days, derived from real-world threat intelligence signals.
Real-World Exposure
starletteReal-time download stats are indexed for npm and PyPI packages. This vulnerability affects PyPI packages — download data is not available via public APIs for these ecosystems.
Description
Summary
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'
Impact
This Denial of service (DoS) vulnerability affects all applications built with Starlette (or FastAPI) accepting form requests.
Affected Packages
| Ecosystem | Package | Vulnerable range | Fix |
|---|---|---|---|
| 🐍PyPI | starlette | all versions | 0.40.0pip install --upgrade 'starlette==0.40.0' |
Detection & mitigation playbook
Open-source dependencyDetect
Scan your dependency tree (package-lock.json, pnpm-lock.yaml, requirements.txt, go.sum, etc.) for starlette, including transitive dependencies — a direct dependency you never call can still pull in a vulnerable version.
Fix
Update starlette to 0.40.0 or later, then make sure no transitive (indirect) dependency still pins the vulnerable range — O3 confirms CVE-2024-47874 is resolved across your whole dependency graph.
Workarounds
If you can't upgrade right away: gate or disable the affected feature, validate untrusted input at the boundary, and avoid passing attacker-controlled data into the vulnerable path. O3's runtime protection blocks exploitation in production as an interim safeguard until the upgrade lands.
How O3 protects you
O3 Security's impact-aware SCA analyses which vulnerable code paths your application actually calls, so a match like CVE-2024-47874 can be triaged on real exposure rather than presence alone.
Tailored to CVE-2024-47874. Runtime protection reduces exposure until a permanent patch is applied and verified — it complements patching, it doesn't replace it.
Frequently Asked Questions
Is CVE-2024-47874 in your dependencies?
O3 Security finds CVE-2024-47874 across PyPI dependencies, including transitive ones, and its impact-aware SCA ranks findings by whether your code actually calls the vulnerable path.