diff --git a/wp-admin/includes/class-wp-upgrader-skins.php b/wp-admin/includes/class-wp-upgrader-skins.php
index 03fffa8af9..9cd665fe4d 100644
--- a/wp-admin/includes/class-wp-upgrader-skins.php
+++ b/wp-admin/includes/class-wp-upgrader-skins.php
@@ -40,12 +40,18 @@ class WP_Upgrader_Skin {
 		$this->result = $result;
 	}
 
-	public function request_filesystem_credentials($error = false) {
+	public function request_filesystem_credentials( $error = false, $context = false, $allow_relaxed_file_ownership = false ) {
 		$url = $this->options['url'];
-		$context = $this->options['context'];
-		if ( !empty($this->options['nonce']) )
+		if ( ! $context ) {
+			$context = $this->options['context'];
+		}
+		if ( !empty($this->options['nonce']) ) {
 			$url = wp_nonce_url($url, $this->options['nonce']);
-		return request_filesystem_credentials($url, '', $error, $context); //Possible to bring inline, Leaving as is for now.
+		}
+
+		$extra_fields = array();
+
+		return request_filesystem_credentials( $url, '', $error, $context, $extra_fields, $allow_relaxed_file_ownership );
 	}
 
 	public function header() {
@@ -699,13 +705,14 @@ class Language_Pack_Upgrader_Skin extends WP_Upgrader_Skin {
 class Automatic_Upgrader_Skin extends WP_Upgrader_Skin {
 	protected $messages = array();
 
-	public function request_filesystem_credentials( $error = false, $context = '' ) {
-		if ( $context )
+	public function request_filesystem_credentials( $error = false, $context = '', $allow_relaxed_file_ownership = false ) {
+		if ( $context ) {
 			$this->options['context'] = $context;
+		}
 		// TODO: fix up request_filesystem_credentials(), or split it, to allow us to request a no-output version
 		// This will output a credentials form in event of failure, We don't want that, so just hide with a buffer
 		ob_start();
-		$result = parent::request_filesystem_credentials( $error );
+		$result = parent::request_filesystem_credentials( $error, $context, $allow_relaxed_file_ownership );
 		ob_end_clean();
 		return $result;
 	}
diff --git a/wp-admin/includes/class-wp-upgrader.php b/wp-admin/includes/class-wp-upgrader.php
index ccd2931f58..3a3cd69dc0 100644
--- a/wp-admin/includes/class-wp-upgrader.php
+++ b/wp-admin/includes/class-wp-upgrader.php
@@ -61,17 +61,19 @@ class WP_Upgrader {
 		$this->strings['maintenance_end'] = __('Disabling Maintenance mode…');
 	}
 
-	public function fs_connect( $directories = array() ) {
+	public function fs_connect( $directories = array(), $allow_relaxed_file_ownership = false ) {
 		global $wp_filesystem;
 
-		if ( false === ($credentials = $this->skin->request_filesystem_credentials()) )
+		if ( false === ( $credentials = $this->skin->request_filesystem_credentials( false, $directories[0], $allow_relaxed_file_ownership ) ) ) {
 			return false;
+		}
 
-		if ( ! WP_Filesystem($credentials) ) {
+		if ( ! WP_Filesystem( $credentials, $directories[0], $allow_relaxed_file_ownership ) ) {
 			$error = true;
 			if ( is_object($wp_filesystem) && $wp_filesystem->errors->get_error_code() )
 				$error = $wp_filesystem->errors;
-			$this->skin->request_filesystem_credentials($error); //Failed to connect, Error and request again
+			// Failed to connect, Error and request again
+			$this->skin->request_filesystem_credentials( $error, $directories[0], $allow_relaxed_file_ownership );
 			return false;
 		}
 
@@ -1456,6 +1458,7 @@ class Core_Upgrader extends WP_Upgrader {
 			'pre_check_md5'    => true,
 			'attempt_rollback' => false,
 			'do_rollback'      => false,
+			'allow_relaxed_file_ownership' => false,
 		);
 		$parsed_args = wp_parse_args( $args, $defaults );
 
@@ -1466,7 +1469,7 @@ class Core_Upgrader extends WP_Upgrader {
 		if ( !isset( $current->response ) || $current->response == 'latest' )
 			return new WP_Error('up_to_date', $this->strings['up_to_date']);
 
-		$res = $this->fs_connect( array(ABSPATH, WP_CONTENT_DIR) );
+		$res = $this->fs_connect( array( ABSPATH, WP_CONTENT_DIR ), $parsed_args['allow_relaxed_file_ownership'] );
 		if ( ! $res || is_wp_error( $res ) ) {
 			return $res;
 		}
@@ -1911,8 +1914,14 @@ class WP_Automatic_Updater {
 		if ( $this->is_disabled() )
 			return false;
 
+		// Only relax the filesystem checks when the update doesn't include new files
+		$allow_relaxed_file_ownership = false;
+		if ( 'core' == $type && isset( $item->new_files ) && ! $item->new_files ) {
+			$allow_relaxed_file_ownership = true;
+		}
+
 		// If we can't do an auto core update, we may still be able to email the user.
-		if ( ! $skin->request_filesystem_credentials( false, $context ) || $this->is_vcs_checkout( $context ) ) {
+		if ( ! $skin->request_filesystem_credentials( false, $context, $allow_relaxed_file_ownership ) || $this->is_vcs_checkout( $context ) ) {
 			if ( 'core' == $type )
 				$this->send_core_update_notification_email( $item );
 			return false;
@@ -2072,6 +2081,11 @@ class WP_Automatic_Updater {
 				break;
 		}
 
+		$allow_relaxed_file_ownership = false;
+		if ( 'core' == $type && isset( $item->new_files ) && ! $item->new_files ) {
+			$allow_relaxed_file_ownership = true;
+		}
+
 		// Boom, This sites about to get a whole new splash of paint!
 		$upgrade_result = $upgrader->upgrade( $upgrader_item, array(
 			'clear_update_cache' => false,
@@ -2079,6 +2093,9 @@ class WP_Automatic_Updater {
 			'pre_check_md5'      => false,
 			// Only available for core updates.
 			'attempt_rollback'   => true,
+			// Allow relaxed file ownership in some scenarios
+			'allow_relaxed_file_ownership' => $allow_relaxed_file_ownership,
+			
 		) );
 
 		// If the filesystem is unavailable, false is returned.
diff --git a/wp-admin/includes/file.php b/wp-admin/includes/file.php
index 6bb05f0ad8..1dfca20573 100644
--- a/wp-admin/includes/file.php
+++ b/wp-admin/includes/file.php
@@ -809,14 +809,15 @@ function copy_dir($from, $to, $skip_list = array() ) {
  *
  * @param array $args (optional) Connection args, These are passed directly to the WP_Filesystem_*() classes.
  * @param string $context (optional) Context for get_filesystem_method(), See function declaration for more information.
+ * @param bool $allow_relaxed_file_ownership Whether to allow Group/World writable.
  * @return null|boolean false on failure, true on success
  */
-function WP_Filesystem( $args = false, $context = false ) {
+function WP_Filesystem( $args = false, $context = false, $allow_relaxed_file_ownership = false ) {
 	global $wp_filesystem;
 
 	require_once(ABSPATH . 'wp-admin/includes/class-wp-filesystem-base.php');
 
-	$method = get_filesystem_method($args, $context);
+	$method = get_filesystem_method( $args, $context, $allow_relaxed_file_ownership );
 
 	if ( ! $method )
 		return false;
@@ -879,25 +880,46 @@ function WP_Filesystem( $args = false, $context = false ) {
  *
  * @param array $args Connection details.
  * @param string $context Full path to the directory that is tested for being writable.
+ * @param bool $allow_relaxed_file_ownership Whether to allow Group/World writable.
  * @return string The transport to use, see description for valid return values.
  */
-function get_filesystem_method($args = array(), $context = false) {
+function get_filesystem_method( $args = array(), $context = false, $allow_relaxed_file_ownership = false ) {
 	$method = defined('FS_METHOD') ? FS_METHOD : false; // Please ensure that this is either 'direct', 'ssh2', 'ftpext' or 'ftpsockets'
 
-	if ( ! $method && function_exists('getmyuid') && function_exists('fileowner') ){
-		if ( !$context )
-			$context = WP_CONTENT_DIR;
+	if ( ! $context ) {
+		$context = WP_CONTENT_DIR;
+	}
 
-		// If the directory doesn't exist (wp-content/languages) then use the parent directory as we'll create it.
-		if ( WP_LANG_DIR == $context && ! is_dir( $context ) )
-			$context = dirname( $context );
+	// If the directory doesn't exist (wp-content/languages) then use the parent directory as we'll create it.
+	if ( WP_LANG_DIR == $context && ! is_dir( $context ) ) {
+		$context = dirname( $context );
+	}
+
+	$context = trailingslashit( $context );
+
+	if ( ! $method ) {
 
-		$context = trailingslashit($context);
 		$temp_file_name = $context . 'temp-write-test-' . time();
 		$temp_handle = @fopen($temp_file_name, 'w');
 		if ( $temp_handle ) {
-			if ( getmyuid() == @fileowner($temp_file_name) )
+
+			// Attempt to determine the file owner of the WordPress files, and that of newly created files
+			$wp_file_owner = $temp_file_owner = false;
+			if ( function_exists('fileowner') ) {
+				$wp_file_owner = @fileowner( __FILE__ );
+				$temp_file_owner = @fileowner( $temp_file_name );
+			}
+
+			if ( $wp_file_owner !== false && $wp_file_owner === $temp_file_owner ) {
+				// WordPress is creating files as the same owner as the WordPress files, 
+				// this means it's safe to modify & create new files via PHP.
 				$method = 'direct';
+			} else if ( $allow_relaxed_file_ownership ) {
+				// The $context directory is writable, and $allow_relaxed_file_ownership is set, this means we can modify files
+				// safely in this directory. This mode doesn't create new files, only alter existing ones.
+				$method = 'direct';
+			}
+
 			@fclose($temp_handle);
 			@unlink($temp_file_name);
 		}
@@ -912,10 +934,12 @@ function get_filesystem_method($args = array(), $context = false) {
 	 *
 	 * @since 2.6.0
 	 *
-	 * @param string $method Filesystem method to return.
-	 * @param array  $args   An array of connection details for the method.
+	 * @param string $method  Filesystem method to return.
+	 * @param array  $args    An array of connection details for the method.
+	 * @param string $context Full path to the directory that is tested for being writable.
+	 * @param bool   $allow_relaxed_file_ownership Whether to allow Group/World writable.
 	 */
-	return apply_filters( 'filesystem_method', $method, $args );
+	return apply_filters( 'filesystem_method', $method, $args, $context, $allow_relaxed_file_ownership );
 }
 
 /**
@@ -933,9 +957,10 @@ function get_filesystem_method($args = array(), $context = false) {
  * @param boolean $error if the current request has failed to connect
  * @param string $context The directory which is needed access to, The write-test will be performed on this directory by get_filesystem_method()
  * @param string $extra_fields Extra POST fields which should be checked for to be included in the post.
+ * @param bool $allow_relaxed_file_ownership Whether to allow Group/World writable.
  * @return boolean False on failure. True on success.
  */
-function request_filesystem_credentials($form_post, $type = '', $error = false, $context = false, $extra_fields = null) {
+function request_filesystem_credentials($form_post, $type = '', $error = false, $context = false, $extra_fields = null, $allow_relaxed_file_ownership = false ) {
 
 	/**
 	 * Filter the filesystem credentials form output.
@@ -952,14 +977,16 @@ function request_filesystem_credentials($form_post, $type = '', $error = false,
 	 *                             Default false.
 	 * @param string $context      Full path to the directory that is tested for
 	 *                             being writable.
+	 * @param bool $allow_relaxed_file_ownership Whether to allow Group/World writable.
 	 * @param array  $extra_fields Extra POST fields.
 	 */
-	$req_cred = apply_filters( 'request_filesystem_credentials', '', $form_post, $type, $error, $context, $extra_fields );
+	$req_cred = apply_filters( 'request_filesystem_credentials', '', $form_post, $type, $error, $context, $extra_fields, $allow_relaxed_file_ownership );
 	if ( '' !== $req_cred )
 		return $req_cred;
 
-	if ( empty($type) )
-		$type = get_filesystem_method(array(), $context);
+	if ( empty($type) ) {
+		$type = get_filesystem_method( array(), $context, $allow_relaxed_file_ownership );
+	}
 
 	if ( 'direct' == $type )
 		return true;
diff --git a/wp-admin/update-core.php b/wp-admin/update-core.php
index 6bab1ca973..ec59a92329 100644
--- a/wp-admin/update-core.php
+++ b/wp-admin/update-core.php
@@ -381,19 +381,23 @@ function do_core_upgrade( $reinstall = false ) {
 	if ( !$update )
 		return;
 
+	// Allow relaxed file ownership writes for User-initiated upgrades when the API specifies
+	// that it's safe to do so. This only happens when there are no new files to create.
+	$allow_relaxed_file_ownership = ! $reinstall && isset( $update->new_files ) && ! $update->new_files;
+
 ?>
 	<div class="wrap">
 	<h2><?php _e('Update WordPress'); ?></h2>
 <?php
 
-	if ( false === ( $credentials = request_filesystem_credentials( $url, '', false, ABSPATH ) ) ) {
+	if ( false === ( $credentials = request_filesystem_credentials( $url, '', false, ABSPATH, array(), $allow_relaxed_file_ownership ) ) ) {
 		echo '</div>';
 		return;
 	}
 
-	if ( ! WP_Filesystem( $credentials, ABSPATH ) ) {
+	if ( ! WP_Filesystem( $credentials, ABSPATH, $allow_relaxed_file_ownership ) ) {
 		// Failed to connect, Error and request again
-		request_filesystem_credentials( $url, '', true, ABSPATH );
+		request_filesystem_credentials( $url, '', true, ABSPATH, array(), $allow_relaxed_file_ownership );
 		echo '</div>';
 		return;
 	}
@@ -411,7 +415,9 @@ function do_core_upgrade( $reinstall = false ) {
 	add_filter( 'update_feedback', 'show_message' );
 
 	$upgrader = new Core_Upgrader();
-	$result = $upgrader->upgrade( $update );
+	$result = $upgrader->upgrade( $update, array(
+		'allow_relaxed_file_ownership' => $allow_relaxed_file_ownership
+	) );
 
 	if ( is_wp_error($result) ) {
 		show_message($result);
diff --git a/wp-includes/update.php b/wp-includes/update.php
index 05a152adb9..bb3b100935 100644
--- a/wp-includes/update.php
+++ b/wp-includes/update.php
@@ -142,7 +142,7 @@ function wp_version_check( $extra_stats = array(), $force_check = false ) {
 				$offer[ $offer_key ] = esc_html( $value );
 		}
 		$offer = (object) array_intersect_key( $offer, array_fill_keys( array( 'response', 'download', 'locale',
-			'packages', 'current', 'version', 'php_version', 'mysql_version', 'new_bundled', 'partial_version', 'notify_email', 'support_email' ), '' ) );
+			'packages', 'current', 'version', 'php_version', 'mysql_version', 'new_bundled', 'partial_version', 'notify_email', 'support_email', 'new_files' ), '' ) );
 	}
 
 	$updates = new stdClass();