Changeset 43989 for branches/4.9/src/wp-includes/functions.php

Timestamp:

12/12/2018 11:02:11 PM (7 years ago)

Author:

jeremyfelt

Message:

Media: Improve verification of MIME file types.

Merges [43988] to the 4.9 branch.

Location:

branches/4.9

Files:

• . (modified) (1 prop)
• src/wp-includes/functions.php (modified) (1 diff)

branches/4.9/src/wp-includes/functions.php

@@ -2342 +2342 @@
         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, $allowed ) ) {
+        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 ( 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;
         }
     }