Thanks for the report. Why is it supposed to be a bug? Seems the behavior is intentional https://github.com/file/file/commit/cee2b49cdb6c995c1a449aa399f80145e28c6a8a in the upstream data. Also wrt RFC 7303 the types are same. The data version depends on the file utility version and a particular distro.

Thanks.

because it's terrible when you have a difference between file in your terminal and PHP caused by the fork of libmagic and bundle it instead using system libraries

this leads to some images reported as applications/octed-stream over now 5 years while a report at the Linux distribution fixed it within days for the cli utility

using Zend memory manager and open-basedir don't justify the fork, the memory manager don't matter, open_basedir should be checked way earlier before calling library code at all and for stream wrappers temp files in the shim layer would be a solution

@spam2, thanks, but that's not the factual feedback on the actual MIME type diff reported.

Cheers.

No feedback was provided. The bug is being suspended because
we assume that you are no longer experiencing the problem.
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information that was requested earlier, please do so and
change the status of the bug back to "Re-Opened". Thank you.

Getting different REAL MIME type from function finfo_file.

The issue may be the different Operating Systems or due to Different PHP versions.

But, While debugging the issue, When I try to upload the XML on localhost I got the text/xml as a real MIME type and on live site it's application/xml.

Below is the debugging steps:

File: /wp-includes/functions.php line 2346

// Validate files that didn't get validated during previous checks.
if ( $type && ! $real_mime && extension_loaded( 'fileinfo' ) ) {
	$finfo = finfo_open( FILEINFO_MIME_TYPE );
	$real_mime = finfo_file( $finfo, $file );
	finfo_close( $finfo );

	// @DEBUGGING...
	echo '<pre>';
	var_dump( FILEINFO_MIME_TYPE ) . '<br/>';
	var_dump( $finfo ) . '<br/>';
	var_dump( $file ) . '<br/>';
	var_dump( $real_mime ) . '<br/>';
	wp_die();
The output of the above code is below on LOCALHOST:

PHP: Version 7.2.4
System: Windows NT M 6.3 build 9600 (Windows 8.1 Professional Edition) i586
int(16)
resource(767) of type (Unknown)
string(46) "C:\Users\Yum\AppData\Local\Temp/wxr-LccAYF.tmp"
string(8) "text/xml"
But, It is different on the LIVE site.

PHP: Version 7.0.32-4+ubuntu16.04.1+deb.sury.org+1
System: Linux ip-172-31-25-204 4.4.0-134-generic #160-Ubuntu SMP Wed Aug 15 14:58:00 UTC 2018 x86_64
int(16)
resource(747) of type (Unknown)
string(19) "/tmp/wxr-YNkiH5.tmp"
string(15) "application/xml"

This is really a regression caused by upstream. 

Now after upgrade to 7.3 I need to refactor constants...