Wordpress/Woocommerce: Sorry, this file type is not permitted for security reasons.

Development Notes: Woocommerce | Sorry, this file type is not permitted for security reasons.

Environment: Wordpress / Woocommerce Problem: Importing product data via CSV results in an error. Importing product data fails. What we tried:

Checking the CSV for correct escaping.
Importing columns separately to isolate the cause.

How we recreated the problem: Insert html markup in one of the columns and attempt to import. Solution for this case: Add this to the bottom of the template functions file to remove the validation. Remove the code after for good general practice.

// Fix for csv being detected as text/html
add_filter( 'wp_check_filetype_and_ext', function( $result, $file, $filename, $mimes, $real_mime ) {
    if ( $result['ext'] == false ) {
        $wp_filetype = wp_check_filetype( $filename, $mimes );
        $ext         = $wp_filetype['ext'];

        if ( $ext == 'csv' && $real_mime == 'text/html' ) {
            $result['ext'] = $ext;
            $result['type'] = 'text/csv';
        }
    }
    return $result;
}, 10, 5 );

Conclusion Commonly relates to the short description and the long description product data columns, due to html markup.