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.

Scores

Faiblesses (CWE)

• CWE-770

Avis

• GHSA-2c2j-9gv5-cj73 — Starlette has possible denial-of-service vector when parsing large files in multipart forms
• PYSEC-2026-1941 — Starlette has possible denial-of-service vector when parsing large files in multipart forms

Références européennes

• ENISA EUVD · EUVD-2025-22159
• GCVE · GCVE-0-2025-54121

Avis du CERT-FR

• CERTFR-2025-AVI-1057 — Multiples vulnérabilités dans les produits VMware · cert.ssi.gouv.fr
• CERTFR-2025-AVI-1051 — Multiples vulnérabilités dans les produits IBM · cert.ssi.gouv.fr

Produits affectés

Références

• https://github.com/encode/starlette/security/advisories/GHSA-2c2j-9gv5-cj73
• https://github.com/encode/starlette/commit/9f7ec2eb512fcc3fe90b43cb9dd9e1d08696bec1
• https://github.com/encode/starlette/blob/fa5355442753f794965ae1af0f87f9fec1b9a3de/starlette/datastructures.py#L436C5-L447C14
• https://github.com/encode/starlette/discussions/2927#discussioncomment-13721403

Sources