CVE-2021-32677
Cross-Site Request Forgery (CSRF) in FastAPI
Description
FastAPI is a web framework for building APIs with Python 3.6+ based on standard Python type hints. FastAPI versions lower than 0.65.2 that used cookies for authentication in path operations that received JSON payloads sent by browsers were vulnerable to a Cross-Site Request Forgery (CSRF) attack. In versions lower than 0.65.2, FastAPI would try to read the request payload as JSON even if the content-type header sent was not set to application/json or a compatible JSON media type (e.g. application/geo+json). A request with a content type of text/plain containing JSON data would be accepted and the JSON data would be extracted. Requests with content type text/plain are exempt from CORS preflights, for being considered Simple requests. The browser will execute them right away including cookies, and the text content could be a JSON string that would be parsed and accepted by the FastAPI application. This is fixed in FastAPI 0.65.2. The request data is now parsed as JSON only if the content-type header is application/json or another JSON compatible media type like application/geo+json. It's best to upgrade to the latest FastAPI, but if updating is not possible then a middleware or a dependency that checks the content-type header and aborts the request if it is not application/json or another JSON compatible content type can act as a mitigating workaround.
How to fix CVE-2021-32677
To remediate CVE-2021-32677, upgrade the affected package to a fixed version below.
- —no fix listed
- —upgrade to 0.65.2 or later
- —upgrade to fa7e3c996edf2d5482fff8f9d890ac2390dede4d or later
Is CVE-2021-32677 being exploited?
Low — EPSS is 0.1%, meaning exploitation activity has not been observed at scale.