If you face with an error stating "Invalid file extension" when you try to upload some file to your concrete5 website, don’t worry. You can fix it by yourself.

I got such error when tried to upload a .zip archive. So here is a solution:

1. Open /concrete/config/base.php

2. Find the following line:

define('UPLOAD_FILE_EXTENSIONS_ALLOWED', '*.flv;*.jpg;*.gif;*.jpeg;*.docx;*.xla;*.png;*.swf;*.doc; *.txt;*.xls;*.csv;*.pdf;*.tiff;*.rtf;*.m4a;*.mov;*.wmv;*.mpeg; *.mpg;*.wav;*.avi;*.mp4;*.mp3;*.qt;*.ppt');

3. Append your extension there, for example, I’ve added ;*.zip :

define('UPLOAD_FILE_EXTENSIONS_ALLOWED', '*.flv;*.jpg;*.gif;*.jpeg;*.docx;*.xla;*.png;*.swf;*.doc; *.txt;*.xls;*.csv;*.pdf;*.tiff;*.rtf;*.m4a;*.mov;*.wmv; *.mpeg;*.mpg;*.wav;*.avi;*.mp4;*.mp3;*.qt;*.ppt;*.zip');

4. Save the file (reupload if you are not editing the file directly).

That’s all. Let me know if it helps anybody.