diff --git a/typo3/sysext/install/Classes/Controller/InstallerController.php b/typo3/sysext/install/Classes/Controller/InstallerController.php
index 1625918b4d1ede71c7d01625d5edbb45b105d108..7eee2b5f39b51eb2deff25db7969de7357b426ca 100644
--- a/typo3/sysext/install/Classes/Controller/InstallerController.php
+++ b/typo3/sysext/install/Classes/Controller/InstallerController.php
@@ -379,8 +379,8 @@ class InstallerController
                     'socket' => $this->getDatabaseConfiguredMysqliSocket(),
                 ]
             );
-            if ($GLOBALS['TYPO3_CONF_VARS']['DB']['Connections'][ConnectionPool::DEFAULT_CONNECTION_NAME]['driver'] === 'mysqli'
-                && $GLOBALS['TYPO3_CONF_VARS']['DB']['Connections'][ConnectionPool::DEFAULT_CONNECTION_NAME]['host'] === 'localhost') {
+            if (($GLOBALS['TYPO3_CONF_VARS']['DB']['Connections'][ConnectionPool::DEFAULT_CONNECTION_NAME]['driver'] ?? '') === 'mysqli'
+                && ($GLOBALS['TYPO3_CONF_VARS']['DB']['Connections'][ConnectionPool::DEFAULT_CONNECTION_NAME]['host'] ?? '') === 'localhost') {
                 $activeAvailableOption = 'mysqliSocketManualConfiguration';
             }
         }
@@ -627,8 +627,8 @@ class InstallerController
     public function checkDatabaseSelectAction(): ResponseInterface
     {
         $success = false;
-        if ((string)$GLOBALS['TYPO3_CONF_VARS']['DB']['Connections'][ConnectionPool::DEFAULT_CONNECTION_NAME]['dbname'] !== ''
-            || (string)$GLOBALS['TYPO3_CONF_VARS']['DB']['Connections'][ConnectionPool::DEFAULT_CONNECTION_NAME]['path'] !== ''
+        if ((string)($GLOBALS['TYPO3_CONF_VARS']['DB']['Connections'][ConnectionPool::DEFAULT_CONNECTION_NAME]['dbname'] ?? '') !== ''
+            || (string)($GLOBALS['TYPO3_CONF_VARS']['DB']['Connections'][ConnectionPool::DEFAULT_CONNECTION_NAME]['path'] ?? '') !== ''
         ) {
             try {
                 $success = GeneralUtility::makeInstance(ConnectionPool::class)
diff --git a/typo3/sysext/install/Classes/Middleware/Installer.php b/typo3/sysext/install/Classes/Middleware/Installer.php
index e008a11d6c7f4cb4a3f78349dd7e797c47ec5eff..9dd24ec66a0313f3d455096df5b79fbf7c5e3db6 100644
--- a/typo3/sysext/install/Classes/Middleware/Installer.php
+++ b/typo3/sysext/install/Classes/Middleware/Installer.php
@@ -87,7 +87,7 @@ class Installer implements MiddlewareInterface
             if ($session->isExpired()) {
                 $session->refreshSession();
             }
-            $postValues = $request->getParsedBody()['install'];
+            $postValues = $request->getParsedBody()['install'] ?? [];
             $sessionTokenOk = false;
             if (empty($postValues)) {
                 // No post data is there, no token check necessary