CVE-2025-54121: Encode Starlette

Medium severity, CVSS 5.3. EPSS: 0.6% chance of exploitation in the next 30 days.

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.

Affected products

• Encode Starlette: before 0.47.2 (fixed in 0.47.2)

Published 2025-07-21. Last modified 2026-06-17.