CVE-2021-32677

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.