Ticket #5560: 5560.3.diff

wp-admin/update.php

@@ -112 +112 @@
 function do_core_upgrade() {
         global $wp_filesystem;
 
-        $url = wp_nonce_url("update.php?action=upgrade-core", "upgrade-core");
+        $url = wp_nonce_url('update.php?action=do-core-upgrade', 'upgrade-core');
         if ( false === ($credentials = request_filesystem_credentials($url)) )
                 return;