What's new in Tornado 6.5.5
===========================

Mar 10, 2026
------------

Security fixes
~~~~~~~~~~~~~~

- ``multipart/form-data`` requests are now limited to 100 parts by default, to prevent a
  denial-of-service attack via very large requests with many parts. This limit is configurable
  via `tornado.httputil.ParseMultipartConfig`. Multipart parsing can also be disabled completely
  if not required for the application. Thanks to [0x-Apollyon](https://github.com/0x-Apollyon) and
  [bekkaze](https://github.com/bekkaze) for reporting this issue.
- The ``domain``, ``path``, and ``samesite`` arguments to `.RequestHandler.set_cookie` are now
  validated for illegal characters, which could be abused to inject other attributes on the cookie.
  Thanks to Dhiral Vyas (Praetorian) for reporting this issue.
- Carriage return characters are no longer accepted in ``multipart/form-data`` headers. Thanks to 
  [sergeykochanov](https://github.com/sergeykochanov) for reporting this issue.