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Valentin Kleibel
controller: Handle UnicodeDecodeError from webob decoding invalid URLs

webob will try to utf-8 decode all %-encoded bytes in URL-parameters, but will
not handle Unicode erors ... and neither did Kallithea. Visiting a URL like
http://localhost:5000/?%AD would thus give an unhandled exception showing
"Internal Server Error" to the user, and logging the full traceback and:

WebApp Error: UnicodeDecodeError: 'utf-8' codec can't decode byte 0xad in position 0: invalid start byte

This has been seen a lot recently from attackers probing for a php
vulnerability
https://devco.re/blog/2024/06/06/security-alert-cve-2024-4577-php-cgi-argument-injection-vulnerability-en/ .

Now handle these exceptions more nicely and reject with "400 Bad Request".
.. _debugging:

===================
Debugging Kallithea
===================

If you encounter problems with Kallithea, here are some instructions
on how to debug them.

.. note:: First make sure you're using the latest version available.


Enable detailed debug
---------------------

Kallithea uses the standard Python ``logging`` module to log its output.
By default only loggers with ``INFO`` level are displayed. To enable full output
change ``level = DEBUG`` for all logging handlers in the currently used .ini file.
This change will allow you to see much more detailed output in the log file or
console. This generally helps a lot to track issues.


Enable interactive debug mode
-----------------------------

To enable interactive debug mode simply comment out ``set debug = false`` in
the .ini file. This will trigger an interactive debugger each time
there is an error in the browser, or send a http link if an error occurred in the backend. This
is a great tool for fast debugging as you get a handy Python console right
in the web view.

.. warning:: NEVER ENABLE THIS ON PRODUCTION! The interactive console
             can be a serious security threat to your system.