GHSA-2c2j-9gv5-cj73

Опубликовано: 21 июл. 2025

Источник: github

Github: Прошло ревью

CVSS3: 5.3

Описание

Starlette has possible denial-of-service vector when parsing large files in multipart forms

Summary

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 we can't accept new connections.

Details

Please see this discussion for details: https://github.com/encode/starlette/discussions/2927#discussioncomment-13721403. In summary the following UploadFile code (copied from here) has a minor bug. Instead of just checking for self._in_memory we should also check if the additional bytes will cause a rollover.

@property def _in_memory(self) -> bool: # check for SpooledTemporaryFile._rolled rolled_to_disk = getattr(self.file, "_rolled", True) return not rolled_to_disk async def write(self, data: bytes) -> None: if self.size is not None: self.size += len(data) if self._in_memory: self.file.write(data) else: await run_in_threadpool(self.file.write, data)

I have already created a PR which fixes the problem: https://github.com/encode/starlette/pull/2962

PoC

See the discussion here for steps on how to reproduce.

Impact

To be honest, very low and not many users will be impacted. Parsing large forms is already CPU intensive so the additional IO block doesn't slow down starlette that much on systems with modern HDDs/SSDs. If someone is running on tape they might see a greater impact.

Ссылки

Пакеты

Наименование

starlette

pip

Затронутые версииВерсия исправления

< 0.47.2

0.47.2

EPSS

Процентиль: 18%

0.00059

Низкий

5.3 Medium

CVSS3

CVE ID

CVE-2025-54121

Дефекты

CWE-770

Связанные уязвимости

CVE-2025-54121

CVSS3: 5.3

ubuntu

около 1 месяца назад

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.