CVE-2024-47874 Starlette Denial of service (DoS) via multipart/form-data
Attackers can cause denial of service in Starlette applications by sending large multipart form fields, exhausting server memory.
- Exploited in the wild
- Not known
- Login needed
- Not needed
- Attackable
- Over the internet
- Victim action needed
- Not needed
- Fix
- Available
What is CVE-2024-47874?
CVE-2024-47874 is a high-severity denial of service vulnerability in encode starlette, published on 15 Oct 2024. An attacker can exploit it over the internet without logging in, with no action from the victim.
Official description
Starlette is an Asynchronous Server Gateway Interface (ASGI) framework/toolkit. Prior to version 0.40.0, 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. This Denial of service (DoS) vulnerability affects all applications built with Starlette (or FastAPI) accepting form requests. Verison 0.40.0 fixes this issue.
Weakness: CWE-770
Which versions are affected by CVE-2024-47874?
3 open source packages ship an affected version, including starlette.
| Package | Affected | Fixed in |
|---|---|---|
starlette PyPI | All versions | 0.40.0 |
starlette PyPI | All versions | 0.40.0 |
starlette PyPI | All versions | 0.40.0 |
Linux distribution packages (3)
python-starlette openSUSE:Leap 15.6 | All versions | 0.35.1-150600.3.3.1 |
python-starlette openSUSE:Tumbleweed | All versions | 0.41.0-1.1 |
python-starlette openSUSE:Tumbleweed | All versions | 1.6.0-1.1 |
How do I fix CVE-2024-47874?
Upgrade starlette to 0.40.0 or later.
Upgrade, then put limits on request size, rate and nesting depth so one client cannot exhaust the service. More about Denial of service.
Is CVE-2024-47874 being exploited?
It is not confirmed as exploited in the wild, but public exploit code for CVE-2024-47874 exists.
Sources
Also known as CLSA-2025-1757031156, CVE-2024-12868, DEBIAN-CVE-2024-47874, GHSA-f96h-pmfr-66vw, PYSEC-2026-1943, ROOT-APP-PYPI-CVE-2024-47874 and 4 more.