diff --git a/admin/index.php b/admin/index.php
index 7b1cd06502b..e78d218a349 100644
--- a/admin/index.php
+++ b/admin/index.php
@@ -47,7 +47,9 @@ if (!function_exists('iconv')) {
 
 define('NO_OUTPUT_BUFFERING', true);
 
-if (empty($_GET['cache']) and empty($_POST['cache']) and empty($_GET['sesskey']) and empty($_POST['sesskey'])) {
+if ((isset($_GET['cache']) and $_GET['cache'] === '0')
+        or (isset($_POST['cache']) and $_POST['cache'] === '0')
+        or (!isset($_POST['cache']) and !isset($_GET['cache']) and empty($_GET['sesskey']) and empty($_POST['sesskey']))) {
     // Prevent caching at all cost when visiting this page directly,
     // we redirect to self once we known no upgrades are necessary.
     // Note: $_GET and $_POST are used here intentionally because our param cleaning is not loaded yet.
@@ -72,9 +74,7 @@ $cache          = optional_param('cache', 0, PARAM_BOOL);
 
 // Set up PAGE.
 $url = new moodle_url('/admin/index.php');
-if ($cache) {
-    $url->param('cache', $cache);
-}
+$url->param('cache', $cache);
 $PAGE->set_url($url);
 unset($url);
 
@@ -249,11 +249,13 @@ if ($version > $CFG->version) {  // upgrade
     $PAGE->set_pagelayout('maintenance');
     $PAGE->set_popup_notification_allowed(false);
 
+    /** @var core_admin_renderer $output */
+    $output = $PAGE->get_renderer('core', 'admin');
+
     if (upgrade_stale_php_files_present()) {
         $PAGE->set_title($stradministration);
         $PAGE->set_cacheable(false);
 
-        $output = $PAGE->get_renderer('core', 'admin');
         echo $output->upgrade_stale_php_files_page();
         die();
     }
@@ -268,7 +270,6 @@ if ($version > $CFG->version) {  // upgrade
         $PAGE->set_heading($strdatabasechecking);
         $PAGE->set_cacheable(false);
 
-        $output = $PAGE->get_renderer('core', 'admin');
         echo $output->upgrade_confirm_page($a->newversion, $maturity, $testsite);
         die();
 
@@ -282,7 +283,6 @@ if ($version > $CFG->version) {  // upgrade
         $PAGE->set_heading($strcurrentrelease);
         $PAGE->set_cacheable(false);
 
-        $output = $PAGE->get_renderer('core', 'admin');
         echo $output->upgrade_environment_page($release, $envstatus, $environment_results);
         die();
 
@@ -296,31 +296,22 @@ if ($version > $CFG->version) {  // upgrade
 
         $reloadurl = new moodle_url('/admin/index.php', array('confirmupgrade' => 1, 'confirmrelease' => 1));
 
-        // check plugin dependencies first
-        $failed = array();
-        if (!plugin_manager::instance()->all_plugins_ok($version, $failed)) {
-            $output = $PAGE->get_renderer('core', 'admin');
-            echo $output->unsatisfied_dependencies_page($version, $failed, $reloadurl);
-            die();
-        }
-        unset($failed);
-
         if ($fetchupdates) {
-            // no sesskey support guaranteed here
-            if (empty($CFG->disableupdatenotifications)) {
-                available_update_checker::instance()->fetch();
+            $updateschecker = available_update_checker::instance();
+            if ($updateschecker->enabled()) {
+                // No sesskey support guaranteed here, because sessions might not work yet.
+                $updateschecker->fetch();
             }
             redirect($reloadurl);
         }
 
-        $output = $PAGE->get_renderer('core', 'admin');
-
         $deployer = available_update_deployer::instance();
         if ($deployer->enabled()) {
             $deployer->initialize($reloadurl, $reloadurl);
 
             $deploydata = $deployer->submitted_data();
             if (!empty($deploydata)) {
+                // No sesskey support guaranteed here, because sessions might not work yet.
                 echo $output->upgrade_plugin_confirm_deploy_page($deployer, $deploydata);
                 die();
             }
@@ -332,7 +323,18 @@ if ($version > $CFG->version) {  // upgrade
         die();
 
     } else {
-        // Launch main upgrade
+        // Always verify plugin dependencies!
+        $failed = array();
+        if (!plugin_manager::instance()->all_plugins_ok($version, $failed)) {
+            $PAGE->set_pagelayout('maintenance');
+            $PAGE->set_popup_notification_allowed(false);
+            $reloadurl = new moodle_url('/admin/index.php', array('confirmupgrade' => 1, 'confirmrelease' => 1, 'cache' => 0));
+            echo $output->unsatisfied_dependencies_page($version, $failed, $reloadurl);
+            die();
+        }
+        unset($failed);
+
+        // Launch main upgrade.
         upgrade_core($version, true);
     }
 } else if ($version < $CFG->version) {
@@ -352,6 +354,10 @@ if ($branch <> $CFG->branch) {  // Update the branch
 if (moodle_needs_upgrading()) {
     if (!$PAGE->headerprinted) {
         // means core upgrade or installation was not already done
+
+        /** @var core_admin_renderer $output */
+        $output = $PAGE->get_renderer('core', 'admin');
+
         if (!$confirmplugins) {
             $strplugincheck = get_string('plugincheck');
 
@@ -363,39 +369,44 @@ if (moodle_needs_upgrading()) {
             $PAGE->set_cacheable(false);
 
             if ($fetchupdates) {
-                // no sesskey support guaranteed here
-                available_update_checker::instance()->fetch();
-                redirect($PAGE->url);
+                $updateschecker = available_update_checker::instance();
+                if ($updateschecker->enabled()) {
+                    require_sesskey();
+                    $updateschecker->fetch();
+                }
+                redirect($reloadurl);
             }
 
-            $output = $PAGE->get_renderer('core', 'admin');
-
             $deployer = available_update_deployer::instance();
             if ($deployer->enabled()) {
                 $deployer->initialize($PAGE->url, $PAGE->url);
 
                 $deploydata = $deployer->submitted_data();
                 if (!empty($deploydata)) {
+                    require_sesskey();
                     echo $output->upgrade_plugin_confirm_deploy_page($deployer, $deploydata);
                     die();
                 }
             }
 
-            // check plugin dependencies first
-            $failed = array();
-            if (!plugin_manager::instance()->all_plugins_ok($version, $failed)) {
-                echo $output->unsatisfied_dependencies_page($version, $failed, $PAGE->url);
-                die();
-            }
-            unset($failed);
-
-            // dependencies check passed, let's rock!
+            // Show plugins info.
             echo $output->upgrade_plugin_check_page(plugin_manager::instance(), available_update_checker::instance(),
                     $version, $showallplugins,
                     new moodle_url($PAGE->url),
                     new moodle_url('/admin/index.php', array('confirmplugincheck'=>1)));
             die();
         }
+
+        // Always verify plugin dependencies!
+        $failed = array();
+        if (!plugin_manager::instance()->all_plugins_ok($version, $failed)) {
+            $PAGE->set_pagelayout('maintenance');
+            $PAGE->set_popup_notification_allowed(false);
+            $reloadurl = new moodle_url('/admin/index.php', array('cache' => 0));
+            echo $output->unsatisfied_dependencies_page($version, $failed, $reloadurl);
+            die();
+        }
+        unset($failed);
     }
     // install/upgrade all plugins and other parts
     upgrade_noncore(true);
@@ -456,6 +467,17 @@ if (during_initial_install()) {
     upgrade_finished('upgradesettings.php');
 }
 
+if (has_capability('moodle/site:config', context_system::instance())) {
+    if ($fetchupdates) {
+        $updateschecker = available_update_checker::instance();
+        if ($updateschecker->enabled()) {
+            require_sesskey();
+            $updateschecker->fetch();
+        }
+        redirect(new moodle_url('/admin/index.php', array('cache' => 0)));
+    }
+}
+
 // Now we can be sure everything was upgraded and caches work fine,
 // redirect if necessary to make sure caching is enabled.
 if (!$cache and !optional_param('sesskey', '', PARAM_RAW)) {
@@ -534,12 +556,6 @@ $registered = $DB->count_records('registration_hubs', array('huburl' => HUB_MOOD
 
 admin_externalpage_setup('adminnotifications');
 
-if ($fetchupdates) {
-    require_sesskey();
-    $updateschecker->fetch();
-    redirect(new moodle_url('/admin/index.php'));
-}
-
 $output = $PAGE->get_renderer('core', 'admin');
 echo $output->admin_notifications_page($maturity, $insecuredataroot, $errorsdisplayed,
         $cronoverdue, $dbproblems, $maintenancemode, $availableupdates, $availableupdatesfetch, $buggyiconvnomb,
diff --git a/admin/renderer.php b/admin/renderer.php
index ad36d346314..6171a69ad59 100644
--- a/admin/renderer.php
+++ b/admin/renderer.php
@@ -170,7 +170,7 @@ class core_admin_renderer extends plugin_renderer_base {
         $output .= $this->environment_check_table($envstatus, $environment_results);
 
         if (!$envstatus) {
-            $output .= $this->upgrade_reload(new moodle_url('/admin/index.php'), array('confirmupgrade' => 1));
+            $output .= $this->upgrade_reload(new moodle_url('/admin/index.php'), array('confirmupgrade' => 1, 'cache' => 0));
 
         } else {
             $output .= $this->notification(get_string('environmentok', 'admin'), 'notifysuccess');
@@ -179,7 +179,7 @@ class core_admin_renderer extends plugin_renderer_base {
                 $output .= $this->box(get_string('langpackwillbeupdated', 'admin'), 'generalbox', 'notice');
             }
 
-            $output .= $this->continue_button(new moodle_url('/admin/index.php', array('confirmupgrade' => 1, 'confirmrelease' => 1)));
+            $output .= $this->continue_button(new moodle_url('/admin/index.php', array('confirmupgrade' => 1, 'confirmrelease' => 1, 'cache' => 0)));
         }
 
         $output .= $this->footer();
@@ -701,7 +701,7 @@ class core_admin_renderer extends plugin_renderer_base {
         }
 
         $updateinfo .= $this->container_start('checkforupdates');
-        $fetchurl = new moodle_url('/admin/index.php', array('fetchupdates' => 1, 'sesskey' => sesskey(), 'cache' => 1));
+        $fetchurl = new moodle_url('/admin/index.php', array('fetchupdates' => 1, 'sesskey' => sesskey(), 'cache' => 0));
         $updateinfo .= $this->single_button($fetchurl, get_string('checkforupdates', 'core_plugin'));
         if ($fetch) {
             $updateinfo .= $this->container(get_string('checkforupdateslast', 'core_plugin',
@@ -952,7 +952,7 @@ class core_admin_renderer extends plugin_renderer_base {
             $out .= $this->output->heading(get_string('nonehighlighted', 'core_plugin'));
             if (empty($options['full'])) {
                 $out .= html_writer::link(new moodle_url('/admin/index.php',
-                    array('confirmupgrade' => 1, 'confirmrelease' => 1, 'showallplugins' => 1)),
+                    array('confirmupgrade' => 1, 'confirmrelease' => 1, 'showallplugins' => 1, 'cache' => 0)),
                     get_string('nonehighlightedinfo', 'core_plugin'));
             }
             $out .= $this->output->container_end();
@@ -962,11 +962,11 @@ class core_admin_renderer extends plugin_renderer_base {
             $out .= $this->output->heading(get_string('somehighlighted', 'core_plugin', $sumofhighlighted));
             if (empty($options['full'])) {
                 $out .= html_writer::link(new moodle_url('/admin/index.php',
-                    array('confirmupgrade' => 1, 'confirmrelease' => 1, 'showallplugins' => 1)),
+                    array('confirmupgrade' => 1, 'confirmrelease' => 1, 'showallplugins' => 1, 'cache' => 0)),
                     get_string('somehighlightedinfo', 'core_plugin'));
             } else {
                 $out .= html_writer::link(new moodle_url('/admin/index.php',
-                    array('confirmupgrade' => 1, 'confirmrelease' => 1, 'showallplugins' => 0)),
+                    array('confirmupgrade' => 1, 'confirmrelease' => 1, 'showallplugins' => 0, 'cache' => 0)),
                     get_string('somehighlightedonly', 'core_plugin'));
             }
             $out .= $this->output->container_end();
diff --git a/lib/pluginlib.php b/lib/pluginlib.php
index f2a8e780c4d..9ca87ec9c3b 100644
--- a/lib/pluginlib.php
+++ b/lib/pluginlib.php
@@ -1035,6 +1035,18 @@ class available_update_checker {
         }
     }
 
+    /**
+     * Is automatic deployment enabled?
+     *
+     * @return bool
+     */
+    public function enabled() {
+        global $CFG;
+
+        // The feature can be prohibited via config.php.
+        return empty($CFG->disableupdateautodeploy);
+    }
+
     /**
      * Returns the timestamp of the last execution of {@link fetch()}
      *
@@ -1810,9 +1822,6 @@ class available_update_info {
  */
 class available_update_deployer {
 
-    const HTTP_PARAM_PREFIX     = 'updteautodpldata_';  // Hey, even Google has not heard of such a prefix! So it MUST be safe :-p
-    const HTTP_PARAM_CHECKER    = 'datapackagesize';    // Name of the parameter that holds the number of items in the received data items
-
     /** @var available_update_deployer holds the singleton instance */
     protected static $singletoninstance;
     /** @var moodle_url URL of a page that includes the deployer UI */
@@ -1985,9 +1994,19 @@ class available_update_deployer {
             throw new coding_exception('Illegal method call - deployer not initialized.');
         }
 
-        $params = $this->data_to_params(array(
-            'updateinfo' => (array)$info,   // see http://www.php.net/manual/en/language.types.array.php#language.types.array.casting
-        ));
+        $params = array(
+            'updateaddon' => $info->component,
+            'version' =>$info->version,
+            'sesskey' => sesskey(),
+        );
+
+        // Append some our own data.
+        if (!empty($this->callerurl)) {
+            $params['callerurl'] = $this->callerurl->out(false);
+        }
+        if (!empty($this->returnurl)) {
+            $params['returnurl'] = $this->returnurl->out(false);
+        }
 
         $widget = new single_button(
             new moodle_url($this->callerurl, $params),
@@ -2079,25 +2098,46 @@ class available_update_deployer {
      * @return array
      */
     public function submitted_data() {
-
-        $data = $this->params_to_data($_POST);
-
-        if (empty($data) or empty($data[self::HTTP_PARAM_CHECKER])) {
+        $component = optional_param('updateaddon', '', PARAM_COMPONENT);
+        $version = optional_param('version', '', PARAM_RAW);
+        if (!$component or !$version) {
             return false;
         }
 
-        if (!empty($data['updateinfo']) and is_object($data['updateinfo'])) {
-            $updateinfo = $data['updateinfo'];
-            if (!empty($updateinfo->component) and !empty($updateinfo->version)) {
-                $data['updateinfo'] = new available_update_info($updateinfo->component, (array)$updateinfo);
+        $plugininfo = plugin_manager::instance()->get_plugin_info($component);
+        if (!$plugininfo) {
+            return false;
+        }
+
+        if ($plugininfo->is_standard()) {
+            return false;
+        }
+
+        if (!$updates = $plugininfo->available_updates()) {
+            return false;
+        }
+
+        $info = null;
+        foreach ($updates as $update) {
+            if ($update->version == $version) {
+                $info = $update;
+                break;
             }
         }
-
-        if (!empty($data['callerurl'])) {
-            $data['callerurl'] = new moodle_url($data['callerurl']);
+        if (!$info) {
+            return false;
         }
 
-        if (!empty($data['returnurl'])) {
+        $data = array(
+            'updateaddon' => $component,
+            'updateinfo'  => $info,
+            'callerurl'   => optional_param('callerurl', null, PARAM_URL),
+            'returnurl'   => optional_param('returnurl', null, PARAM_URL),
+        );
+        if ($data['callerurl']) {
+            $data['callerurl'] = new moodle_url($data['callerurl']);
+        }
+        if ($data['callerurl']) {
             $data['returnurl'] = new moodle_url($data['returnurl']);
         }
 
@@ -2196,62 +2236,6 @@ class available_update_deployer {
         }
     }
 
-    // End of external API
-
-    /**
-     * Prepares an array of HTTP parameters that can be passed to another page.
-     *
-     * @param array|object $data associative array or an object holding the data, data JSON-able
-     * @return array suitable as a param for moodle_url
-     */
-    protected function data_to_params($data) {
-
-        // Append some our own data
-        if (!empty($this->callerurl)) {
-            $data['callerurl'] = $this->callerurl->out(false);
-        }
-        if (!empty($this->returnurl)) {
-            $data['returnurl'] = $this->returnurl->out(false);
-        }
-
-        // Finally append the count of items in the package.
-        $data[self::HTTP_PARAM_CHECKER] = count($data);
-
-        // Generate params
-        $params = array();
-        foreach ($data as $name => $value) {
-            $transname = self::HTTP_PARAM_PREFIX.$name;
-            $transvalue = json_encode($value);
-            $params[$transname] = $transvalue;
-        }
-
-        return $params;
-    }
-
-    /**
-     * Converts HTTP parameters passed to the script into native PHP data
-     *
-     * @param array $params such as $_REQUEST or $_POST
-     * @return array data passed for this class
-     */
-    protected function params_to_data(array $params) {
-
-        if (empty($params)) {
-            return array();
-        }
-
-        $data = array();
-        foreach ($params as $name => $value) {
-            if (strpos($name, self::HTTP_PARAM_PREFIX) === 0) {
-                $realname = substr($name, strlen(self::HTTP_PARAM_PREFIX));
-                $realvalue = json_decode($value);
-                $data[$realname] = $realvalue;
-            }
-        }
-
-        return $data;
-    }
-
     /**
      * Returns a random string to be used as a filename of the password storage.
      *