Upload files : docx file detect as zip file

[rutonyru]

Hi,
I'm facing a trouble I would like to discuss with you.
For reasons I don't understand, when I try to upload a docx file, the server detects it as a zip file. As I don't allow zip extension in my validator, I get an error. If I change the validator to accept zip extension, the server allow the file to be treated.
I try it with Bruno, but the file is correctly detect (as a docx). I have the trouble when the client is a web app in firefox (ok with chrome and edge).
Of course, I don't want to accept zip files in my application so I have to understand how I can manage this case.
Could it be a configuration of the file validator to manage the zip dectection ? I can imagine there is an verification of the real file 'type' and docx is a zip file.
Do you have any idea ?
Thanks,
Antoine