Index: typo3/sysext/install/mod/class.tx_install.php
===================================================================
--- typo3/sysext/install/mod/class.tx_install.php	(revision 8810)
+++ typo3/sysext/install/mod/class.tx_install.php	(working copy)
@@ -231,6 +231,18 @@
 		'logout' => 'Logout from Install Tool',
 	);
 
+	protected $requiredModules = array(	// PHP modules which are required
+		'filter',
+		'gd',
+		'json',
+		'mysql',
+		'pcre',
+		'session',
+		'SPL',
+		'standard',
+		'xml',
+		'zlib'
+	);
 
 
 
@@ -261,6 +273,12 @@
 		$this->mode = t3lib_div::_GP('mode');
 		if ($this->mode !== '123') {
 			$this->mode = '';
+		} else {
+			$missingPHPModules = $this->getMissingPHPModules();
+			if (count($missingPHPModules) > 0) {
+				t3lib_BEfunc::typo3PrintError('TYPO3 Installation Error', 'The following PHP module(s) is/are missing: ' . implode(', ', $missingPHPModules));
+				die();
+			}
 		}
 		if (t3lib_div::_GP('step') === 'go') {
 			$this->step = 'go';
@@ -4115,8 +4133,41 @@
 		return (is_array($test) ? 1 : 0);
 	}
 
+	/**
+	 * Checks if the essential PHP modules are loaded
+	 *
+	 * @return array list of modules which are missing
+	 */
+	protected function getMissingPHPModules() {
 
+			// Hook to adjust the required PHP modules in the 1-2-3 installer
+		if (is_array ($GLOBALS['TYPO3_CONF_VARS']['SC_OPTIONS']['ext/install/mod/class.tx_install.php']['requiredModules'])) {
+			foreach ($GLOBALS['TYPO3_CONF_VARS']['SC_OPTIONS']['ext/install/mod/class.tx_install.php']['requiredModules'] as $classData) {
+				$hookObject = t3lib_div::getUserObj($classData);
+				$this->requiredModules = $hookObject->setRequiredModules($this);
+			}
+		}
 
+		$result = array();
+		foreach ($this->requiredModules as $module) {
+			if (is_array($module)) {
+				$detectedSubmodules = FALSE;
+				foreach ($module as $submodule) {
+					if (extension_loaded($submodule)) {
+						$detectedSubmodules = TRUE;
+					}
+				}
+				if ($detectedSubmodules === FALSE) {
+					$result[] = 'one of: (' . implode(', ', $module) . ')';
+				}
+			} else {
+				if (!extension_loaded($module)) {
+					$result[] = $module;
+				}
+			}
+		}
+		return $result;
+	}
 
 
 
@@ -4125,6 +4176,7 @@
 
 
 
+
 	/*****************************************
 	 *
 	 * ABOUT the isXXX functions.