Important: #106735 - File MIME Type compatiblity mapping

Description

With forge#106240 mime type hardening has been established in order to ensure that file extensions of uploaded files and their contents are consistent in order to avoid sneaking in malicious files with faked file extensions or to bypass file extension limitations.

Since PHP file detection methods can not reliable detect all IANA defined MIME types, mime-db based heuristics are now applied to map generic MIME types like text/plain to text/csv for *.csv files.

This mapping has been made adjustable for MIME types via $GLOBALS['TYPO3_CONF_VARS']['SYS']['FileInfo']['mimeTypeCompatibility'] where for each generic MIME type (as detected by PHP MIME type detection) a map from file extension to allowed concrete MIME type can be supplied.

// Example that is already shipped with TYPO3, a *.jfif file that is
// detected as image/jpeg is mapped to image/pjpeg, which is the
// defined MIME type per IANA and enforced by the FAL persistence layer.
$GLOBALS['TYPO3_CONF_VARS']['SYS']['FileInfo']['mimeTypeCompatibility']['image/jpeg']['jfif'] =
    'image/pjpeg';

// Generic example, which allows a file ending in `*.foo` that is detected
// to contain text/plain contents to be mapped to the MIME type text/x-foo,
// other contents (e.g. if the file contains binary data) will not be mapped
$GLOBALS['TYPO3_CONF_VARS']['SYS']['FileInfo']['mimeTypeCompatibility']['text/plain']['foo'] =
    'text/x-foo';