GHSA-f96h-pmfr-66vw is a none-severity (CVSS 0) CWE-770 vulnerability in starlette. O3 Security confirms whether GHSA-f96h-pmfr-66vw is actually reachable in your code before you act, and blocks exploitation at runtime until you patch.
Starlette Denial of service (DoS) via multipart/form-data
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 | 0.40.0 |
Detection & mitigation playbook
Open-source dependencyDetect
Scan your dependency tree (package-lock.json, pnpm-lock.yaml, requirements.txt, go.sum, etc.) for starlette. O3's reachability analysis confirms whether the vulnerable code path is actually invoked in your application, so you act on real exposure instead of every transitive match.
Fix
Update starlette to 0.40.0 or later, then make sure no transitive (indirect) dependency still pins the vulnerable range — O3 confirms GHSA-f96h-pmfr-66vw 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 pinpoints whether GHSA-f96h-pmfr-66vw is reachable in your code and exactly where to fix it, then blocks exploitation in production at runtime until the patched version is deployed.
Tailored to GHSA-f96h-pmfr-66vw. Runtime protection reduces exposure until a permanent patch is applied and verified — it complements patching, it doesn't replace it.
Frequently Asked Questions
Is GHSA-f96h-pmfr-66vw in your dependencies?
O3 detects GHSA-f96h-pmfr-66vw across PyPI dependencies and uses function-level reachability to confirm whether the vulnerable code path is actually reachable — not just present. No false positives.