diff --git a/wp-admin/admin-ajax.php b/wp-admin/admin-ajax.php
index d2a8d4d20c..a7e0b48dd0 100644
--- a/wp-admin/admin-ajax.php
+++ b/wp-admin/admin-ajax.php
@@ -396,7 +396,7 @@ case 'delete-meta' :
 	if ( !$meta = get_post_meta_by_id( $id ) )
 		die('1');
 
-	if ( !current_user_can( 'edit_post', $meta->post_id ) )
+	if ( !current_user_can( 'edit_post', $meta->post_id ) || is_protected_meta( $meta->meta_key ) )
 		die('-1');
 	if ( delete_meta( $meta->meta_id ) )
 		die('1');
@@ -855,6 +855,8 @@ case 'add-meta' :
 			die('0'); // if meta doesn't exist
 		if ( !current_user_can( 'edit_post', $meta->post_id ) )
 			die('-1');
+		if ( is_protected_meta( $meta->meta_key ) )
+			die('-1');
 		if ( $meta->meta_value != stripslashes($value) || $meta->meta_key != stripslashes($key) ) {
 			if ( !$u = update_meta( $mid, $key, $value ) )
 				die('0'); // We know meta exists; we also know it's unchanged (or DB error, in which case there are bigger problems).
diff --git a/wp-admin/includes/media.php b/wp-admin/includes/media.php
index c9d603ea8f..7e27ded133 100644
--- a/wp-admin/includes/media.php
+++ b/wp-admin/includes/media.php
@@ -1192,7 +1192,7 @@ function get_media_item( $attachment_id, $args = null ) {
 	$toggle_on  = __( 'Show' );
 	$toggle_off = __( 'Hide' );
 
-	$filename = basename( $post->guid );
+	$filename = esc_html( basename( $post->guid ) );
 	$title = esc_attr( $post->post_title );
 
 	if ( $_tags = get_the_tags( $attachment_id ) ) {
diff --git a/wp-admin/includes/post.php b/wp-admin/includes/post.php
index 12cbaa0f92..93606fa5d8 100644
--- a/wp-admin/includes/post.php
+++ b/wp-admin/includes/post.php
@@ -138,6 +138,7 @@ function edit_post( $post_data = null ) {
 	$post_ID = (int) $post_data['post_ID'];
 	$post = get_post( $post_ID );
 	$post_data['post_type'] = $post->post_type;
+	$post_data['post_mime_type'] = $post->post_mime_type;
 
 	$ptype = get_post_type_object($post_data['post_type']);
 	if ( !current_user_can( $ptype->cap->edit_post, $post_ID ) ) {
@@ -199,6 +200,8 @@ function edit_post( $post_data = null ) {
 				continue;
 			if ( $meta->post_id != $post_ID )
 				continue;
+			if ( is_protected_meta( $key ) )
+				continue;
 			update_meta( $key, $value['key'], $value['value'] );
 		}
 	}
@@ -209,6 +212,8 @@ function edit_post( $post_data = null ) {
 				continue;
 			if ( $meta->post_id != $post_ID )
 				continue;
+			if ( is_protected_meta( $key ) )
+				continue;
 			delete_meta( $key );
 		}
 	}
@@ -527,6 +532,8 @@ function wp_write_post() {
 			return new WP_Error( 'edit_posts', __( 'You are not allowed to create posts or drafts on this site.' ) );
 	}
 
+	$_POST['post_mime_type'] = '';
+
 	// Check for autosave collisions
 	// Does this need to be updated? ~ Mark
 	$temp_id = false;
@@ -632,8 +639,6 @@ function add_meta( $post_ID ) {
 	global $wpdb;
 	$post_ID = (int) $post_ID;
 
-	$protected = array( '_wp_attached_file', '_wp_attachment_metadata', '_wp_old_slug', '_wp_page_template' );
-
 	$metakeyselect = isset($_POST['metakeyselect']) ? stripslashes( trim( $_POST['metakeyselect'] ) ) : '';
 	$metakeyinput = isset($_POST['metakeyinput']) ? stripslashes( trim( $_POST['metakeyinput'] ) ) : '';
 	$metavalue = isset($_POST['metavalue']) ? maybe_serialize( stripslashes_deep( $_POST['metavalue'] ) ) : '';
@@ -650,7 +655,7 @@ function add_meta( $post_ID ) {
 		if ( $metakeyinput)
 			$metakey = $metakeyinput; // default
 
-		if ( in_array($metakey, $protected) )
+		if ( is_protected_meta( $metakey ) )
 			return false;
 
 		wp_cache_delete($post_ID, 'post_meta');
@@ -756,11 +761,9 @@ function has_meta( $postid ) {
 function update_meta( $meta_id, $meta_key, $meta_value ) {
 	global $wpdb;
 
-	$protected = array( '_wp_attached_file', '_wp_attachment_metadata', '_wp_old_slug', '_wp_page_template' );
-
 	$meta_key = stripslashes($meta_key);
 
-	if ( in_array($meta_key, $protected) )
+	if ( is_protected_meta( $meta_key ) )
 		return false;
 
 	if ( '' === trim( $meta_value ) )
diff --git a/wp-admin/includes/template.php b/wp-admin/includes/template.php
index b345c36b76..2f16b3c125 100644
--- a/wp-admin/includes/template.php
+++ b/wp-admin/includes/template.php
@@ -465,6 +465,10 @@ function list_meta( $meta ) {
  */
 function _list_meta_row( $entry, &$count ) {
 	static $update_nonce = false;
+
+	if ( is_protected_meta( $entry['meta_key'] ) )
+		return;
+
 	if ( !$update_nonce )
 		$update_nonce = wp_create_nonce( 'add-meta' );
 
diff --git a/wp-includes/default-filters.php b/wp-includes/default-filters.php
index e3e5dfba12..30c145b320 100644
--- a/wp-includes/default-filters.php
+++ b/wp-includes/default-filters.php
@@ -58,14 +58,14 @@ foreach ( array( 'comment_author_email', 'user_email' ) as $filter ) {
 
 // Save URL
 foreach ( array( 'pre_comment_author_url', 'pre_user_url', 'pre_link_url', 'pre_link_image',
-	'pre_link_rss' ) as $filter ) {
+	'pre_link_rss', 'pre_post_guid' ) as $filter ) {
 	add_filter( $filter, 'wp_strip_all_tags' );
 	add_filter( $filter, 'esc_url_raw'       );
 	add_filter( $filter, 'wp_filter_kses'    );
 }
 
 // Display URL
-foreach ( array( 'user_url', 'link_url', 'link_image', 'link_rss', 'comment_url' ) as $filter ) {
+foreach ( array( 'user_url', 'link_url', 'link_image', 'link_rss', 'comment_url', 'post_guid' ) as $filter ) {
 	if ( is_admin() )
 		add_filter( $filter, 'wp_strip_all_tags' );
 	add_filter( $filter, 'esc_url'           );
@@ -86,6 +86,10 @@ foreach ( array( 'pre_post_status', 'pre_post_comment_status', 'pre_post_ping_st
 	add_filter( $filter, 'sanitize_key' );
 }
 
+// Mime types
+add_filter( 'pre_post_mime_type', 'sanitize_mime_type' );
+add_filter( 'post_mime_type', 'sanitize_mime_type' );
+
 // Places to balance tags on input
 foreach ( array( 'content_save_pre', 'excerpt_save_pre', 'comment_save_pre', 'pre_comment_content' ) as $filter ) {
 	add_filter( $filter, 'balanceTags', 50 );
diff --git a/wp-includes/formatting.php b/wp-includes/formatting.php
index 1aad3b79fa..d0a0e3c8da 100644
--- a/wp-includes/formatting.php
+++ b/wp-includes/formatting.php
@@ -2903,4 +2903,17 @@ function capital_P_dangit( $text ) {
 
 }
 
+/**
+ * Sanitize a mime type
+ *
+ * @since 3.2.0
+ *
+ * @param string $mime_type Mime type
+ * @return string Sanitized mime type
+ */
+function sanitize_mime_type( $mime_type ) {
+	$sani_mime_type = preg_replace( '/[^-*.a-zA-Z0-9\/]/', '', $mime_type );
+	return apply_filters( 'sanitize_mime_type', $sani_mime_type, $mime_type );
+}
+
 ?>
diff --git a/wp-includes/meta.php b/wp-includes/meta.php
index 27a1288187..6c10cb6b81 100644
--- a/wp-includes/meta.php
+++ b/wp-includes/meta.php
@@ -45,6 +45,7 @@ function add_metadata($meta_type, $object_id, $meta_key, $meta_value, $unique =
 	// expected_slashed ($meta_key)
 	$meta_key = stripslashes($meta_key);
 	$meta_value = stripslashes_deep($meta_value);
+	$meta_value = sanitize_meta( $meta_key, $meta_value, $meta_type );
 
 	$check = apply_filters( "add_{$meta_type}_metadata", null, $object_id, $meta_key, $meta_value, $unique );
 	if ( null !== $check )
@@ -113,6 +114,7 @@ function update_metadata($meta_type, $object_id, $meta_key, $meta_value, $prev_v
 	// expected_slashed ($meta_key)
 	$meta_key = stripslashes($meta_key);
 	$meta_value = stripslashes_deep($meta_value);
+	$meta_value = sanitize_meta( $meta_key, $meta_value, $meta_type );
 
 	$check = apply_filters( "update_{$meta_type}_metadata", null, $object_id, $meta_key, $meta_value, $prev_value );
 	if ( null !== $check )
@@ -488,4 +490,33 @@ function _get_meta_table($type) {
 
 	return $wpdb->$table_name;
 }
+
+/**
+ * Determine whether a meta key is protected
+ *
+ * @since 3.2.0
+ *
+ * @param string $meta_key Meta key
+ * @return bool True if the key is protected, false otherwise.
+ */
+function is_protected_meta( $meta_key, $meta_type = null ) {
+	$protected = (  '_' == $meta_key[0] );
+
+	return apply_filters( 'is_protected_meta', $protected, $meta_key, $meta_type );
+}
+
+/**
+ * Sanitize meta value
+ *
+ * @since 3.2.0
+ *
+ * @param string $meta_key Meta key
+ * @param mixed $meta_value Meta value to sanitize
+ * @param string $meta_type Type of meta
+ * @return mixed Sanitized $meta_value
+ */
+function sanitize_meta( $meta_key, $meta_value, $meta_type = null ) {
+	return apply_filters( 'sanitize_meta', $meta_value, $meta_key, $meta_type );
+}
+
 ?>
diff --git a/wp-includes/theme.php b/wp-includes/theme.php
index c2960557db..14176ac712 100644
--- a/wp-includes/theme.php
+++ b/wp-includes/theme.php
@@ -1435,7 +1435,7 @@ function get_header_image() {
 	else
 		$url = str_replace( 'https://', 'http://', $url );
 
-	return $url;
+	return esc_url_raw( $url );
 }
 
 /**