CVE-2025-54121

Starlette is a lightweight ASGI (Asynchronous Server Gateway Interface) framework/toolkit, designed for building async web services in Python. In versions 0.47.1 and below, when parsing a multi-part form with large files (greater than the default max spool size) starlette will block the main thread to roll the file over to disk. This blocks the event thread which means the application can't accept new connections. The UploadFile code has a minor bug where instead of just checking for self._in_memory, the logic should also check if the additional bytes will cause a rollover. The vulnerability is fixed in version 0.47.2.

The following products are affected by CVE-2025-54121 vulnerability.

Here, you will find a curated list of external links that provide in-depth information to CVE-2025-54121.

URL	Resource
https://github.com/encode/starlette/blob/fa5355442753f794965ae1af0f87f9fec1b9a3de/starlette/datastructures.py#L436C5-L447C14
https://github.com/encode/starlette/commit/9f7ec2eb512fcc3fe90b43cb9dd9e1d08696bec1
https://github.com/encode/starlette/discussions/2927#discussioncomment-13721403
https://github.com/encode/starlette/security/advisories/GHSA-2c2j-9gv5-cj73
https://nvd.nist.gov/vuln/detail/CVE-2025-54121
https://www.cve.org/CVERecord?id=CVE-2025-54121