CVE-2025-54121
Starlette has possible denial-of-service vector when parsing large files in multipart forms
Description
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.
How to fix CVE-2025-54121
To remediate CVE-2025-54121, upgrade the affected package to a fixed version below.
- —no fix listed
- —upgrade to 0.47.2 or later
Is CVE-2025-54121 being exploited?
Low — EPSS is 0.3%, meaning exploitation activity has not been observed at scale.
Affected packages (2)
- from 0
- from 0, < 0.47.2
CVSS scores
| Source | Version | Severity | Vector |
|---|---|---|---|
| osv | CVSS 3.1 | MEDIUM5.3 | CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:L |