Index: typo3/sysext/install/mod/class.tx_install.php
===================================================================
--- typo3/sysext/install/mod/class.tx_install.php	(revision 8132)
+++ typo3/sysext/install/mod/class.tx_install.php	(working copy)
@@ -261,6 +261,11 @@
 		$this->mode = t3lib_div::_GP('mode');
 		if ($this->mode !== '123') {
 			$this->mode = '';
+		} else {
+			$missingPHPModules = $this->getMissingPHPModules();
+			if (count($missingPHPModules) > 0) {
+				die('The following PHP module(s) is/are missing: ' . implode(', ', $missingPHPModules));
+			}
 		}
 		if (t3lib_div::_GP('step') === 'go') {
 			$this->step = 'go';
@@ -4111,6 +4116,52 @@
 		return (is_array($test) ? 1 : 0);
 	}
 
+	/**
+	 * Checks if the essential PHP modules are loaded
+	 *
+	 * @return array list of modules which are missing
+	 */
+	protected function getMissingPHPModules() {
+			// filter, gd, json, mysql, pcre, session, spl, xml, zlib
+		$result = array();
+		if (!function_exists('filter_list')) {
+				// filter_list is added by filter module in PHP >= 5.2.0
+			$result[] = 'filter';
+		}
+		if (!function_exists('gd_info')) {
+				// gd_info is added by gd module in PHP >= 4.3.0
+			$result[] = 'gd';
+		}
+		if (!function_exists('json_decode')) {
+				// json_decode is added by json module in PHP >= 5.2.0 / PECL json >= 1.2.0
+			$result[] = 'json';
+		}
+		if (!function_exists('mysql_connect')) {
+				// mysql_connect is added by mysql module in PHP 4/5
+			$result[] = 'mysql';
+		}
+		if (!function_exists('preg_match')) {
+				// preg_match is added by pcre module in PHP 4/5
+			$result[] = 'pcre';
+		}
+		if (!function_exists('session_start')) {
+				// session_start is added by session module in PHP 4/5
+			$result[] = 'session';
+		}
+		if (!function_exists('spl_classes')) {
+				// spl_classes is added by spl module in PHP 5
+			$result[] = 'spl';
+		}
+		if (!function_exists('xml_parse')) {
+				// xml_parse is added by xml module in PHP 4/5
+			$result[] = 'xml parser';
+		}
+		if (!function_exists('gzinflate')) {
+				// gzinflate is added by zlib module in PHP >= 4.0.4
+			$result[] = 'zlib';
+		}
+		return $result;
+	}
 
 
 
@@ -4120,7 +4171,6 @@
 
 
 
-
 	/*****************************************
 	 *
 	 * ABOUT the isXXX functions.