Media: Improve verification of MIME file types.

Merges [43988] to the 4.9 branch.


git-svn-id: https://develop.svn.wordpress.org/branches/4.9@43989 602fd350-edb4-49c9-b593-d223f7449a82

Author: jeremyfelt

src/wp-includes/functions.php

@@ -2341,17 +2341,52 @@ function wp_check_filetype_and_ext( $file, $filename, $mimes = null ) {
 		$real_mime = finfo_file( $finfo, $file );
 		finfo_close( $finfo );
 
+		// fileinfo often misidentifies obscure files as one of these types
+		$nonspecific_types = array(
+			'application/octet-stream',
+			'application/encrypted',
+			'application/CDFV2-encrypted',
+			'application/zip',
+		);
+
 		/*
-		 * If $real_mime doesn't match what we're expecting, we need to do some extra
-		 * vetting of application mime types to make sure this type of file is allowed.
-		 * Other mime types are assumed to be safe, but should be considered unverified.
+		 * If $real_mime doesn't match the content type we're expecting from the file's extension,
+		 * we need to do some additional vetting. Media types and those listed in $nonspecific_types are
+		 * allowed some leeway, but anything else must exactly match the real content type.
 		 */
-		if ( $real_mime && ( $real_mime !== $type ) && ( 0 === strpos( $real_mime, 'application' ) ) ) {
-			$allowed = get_allowed_mime_types();
+		if ( in_array( $real_mime, $nonspecific_types, true ) ) {
+			// File is a non-specific binary type. That's ok if it's a type that generally tends to be binary.
+			if ( !in_array( substr( $type, 0, strcspn( $type, '/' ) ), array( 'application', 'video', 'audio' ) ) ) {
+				$type = $ext = false;
+			}
+		} elseif ( 0 === strpos( $real_mime, 'video/' ) || 0 === strpos( $real_mime, 'audio/' ) ) {
+			/*
+			 * For these types, only the major type must match the real value.
+			 * This means that common mismatches are forgiven: application/vnd.apple.numbers is often misidentified as application/zip,
+			 * and some media files are commonly named with the wrong extension (.mov instead of .mp4)
+			 */
 
-			if ( ! in_array( $real_mime, $allowed ) ) {
+			if ( substr( $real_mime, 0, strcspn( $real_mime, '/' ) ) !== substr( $type, 0, strcspn( $type, '/' ) ) ) {
+				$type = $ext = false;
+			}
+		} else {
+			if ( $type !== $real_mime ) {
+				/*
+				 * Everything else including image/* and application/*: 
+				 * If the real content type doesn't match the file extension, assume it's dangerous.
+				 */
 				$type = $ext = false;
 			}
+
+		}
+	}
+
+	// The mime type must be allowed 
+	if ( $type ) {
+		$allowed = get_allowed_mime_types();
+
+		if ( ! in_array( $type, $allowed ) ) {
+			$type = $ext = false;
 		}
 	}
 

tests/phpunit/tests/functions.php

@@ -1115,8 +1115,8 @@ public function _wp_check_filetype_and_ext_data() {
 				DIR_TESTDATA . '/formatting/big5.txt',
 				'big5.jpg',
 				array(
-					'ext' => 'jpg',
-					'type' => 'image/jpeg',
+					'ext' => false,
+					'type' => false,
 					'proper_filename' => false,
 				),
 			),
@@ -1130,6 +1130,26 @@ public function _wp_check_filetype_and_ext_data() {
 					'proper_filename' => false,
 				),
 			),
+			// Non-image file not allowed even if it's named like one.
+			array(
+				DIR_TESTDATA . '/export/crazy-cdata.xml',
+				'crazy-cdata.jpg',
+				array(
+					'ext' => false,
+					'type' => false,
+					'proper_filename' => false,
+				),
+			),
+			// Non-image file not allowed if it's named like something else.
+			array(
+				DIR_TESTDATA . '/export/crazy-cdata.xml',
+				'crazy-cdata.doc',
+				array(
+					'ext' => false,
+					'type' => false,
+					'proper_filename' => false,
+				),
+			),
 		);
 
 		// Test a few additional file types on single sites.