(Tornado is a Python web framework and asynchronous networking library. ...)

A flaw was found in tornado-python. A remote attacker can exploit this vulnerability by sending a specially crafted, very large multipart body with numerous parts. Because the parsing of these large bodies occurs synchronously on the main thread, it can consume excessive resources, leading to a denial of service (DoS) for the application.

Tornado is a Python web framework and asynchronous networking library. In versions of Tornado prior to 6.5.5, the only limit on the number of parts in multipart/form-data is the max_body_size setting (default 100MB). Since parsing occurs synchronously on the main thread, this creates the possibility of denial-of-service due to the cost of parsing very large multipart bodies with many parts. This vulnerability is fixed in 6.5.5.

Tornado is a Python web framework and asynchronous networking library. ...

Tornado is vulnerable to DoS due to too many multipart parts