diff --git a/core/Core.php b/core/Core.php
index 4c5236f4f..3959fb76e 100755
--- a/core/Core.php
+++ b/core/Core.php
@@ -173,6 +173,7 @@ define('ASSETS_PATH', BASE_PATH . '/' . ASSETS_DIR);
 /**
  * Define the temporary folder if it wasn't defined yet
  */
+require_once('core/TempPath.php');
 if(!defined('TEMP_FOLDER')) {
 	define('TEMP_FOLDER', getTempFolder());
 }
@@ -254,65 +255,6 @@ Debug::loadErrorHandlers();
 ///////////////////////////////////////////////////////////////////////////////
 // HELPER FUNCTIONS
 
-function getSysTempDir() {
-	if(function_exists('sys_get_temp_dir')) {
-		$sysTmp = sys_get_temp_dir();
-	} elseif(isset($_ENV['TMP'])) {
-		$sysTmp = $_ENV['TMP'];    	
-	} else {
-		$tmpFile = tempnam('adfadsfdas','');
-		unlink($tmpFile);
-		$sysTmp = dirname($tmpFile);
-	}
-	return $sysTmp;
-}
-
-/**
- * Returns the temporary folder that sapphire/silverstripe should use for its cache files
- * This is loaded into the TEMP_FOLDER define on start up
- * 
- * @param $base The base path to use as the basis for the temp folder name.  Defaults to BASE_PATH,
- * which is usually fine; however, the $base argument can be used to help test.
- */
-function getTempFolder($base = null) {
-	if(!$base) $base = BASE_PATH;
-
-	if($base) {
-		$cachefolder = "silverstripe-cache" . str_replace(array(' ', "/", ":", "\\"), "-", $base);
-	} else {
-		$cachefolder = "silverstripe-cache";
-	}
-
-	$ssTmp = BASE_PATH . "/silverstripe-cache";
-	if(@file_exists($ssTmp)) {
-		return $ssTmp;
-	}
-
-	$sysTmp = getSysTempDir();
-	$worked = true;
-	$ssTmp = "$sysTmp/$cachefolder";
-
-	if(!@file_exists($ssTmp)) {
-		@$worked = mkdir($ssTmp);
-	}
-
-	if(!$worked) {
-		$ssTmp = BASE_PATH . "/silverstripe-cache";
-		$worked = true;
-		if(!@file_exists($ssTmp)) {
-			@$worked = mkdir($ssTmp);
-		}
-	}
-
-	if(!$worked) {
-		user_error("Permission problem gaining access to a temp folder. " .
-			"Please create a folder named silverstripe-cache in the base folder "  .
-			"of the installation and ensure it has the correct permissions", E_USER_ERROR);
-	}
-
-	return $ssTmp;
-}
-
 /**
  * Return the file where that class is stored.
  * 
diff --git a/core/TempPath.php b/core/TempPath.php
new file mode 100644
index 000000000..c3b0a111d
--- /dev/null
+++ b/core/TempPath.php
@@ -0,0 +1,60 @@
+<?php
+
+function getSysTempDir() {
+	if(function_exists('sys_get_temp_dir')) {
+		$sysTmp = sys_get_temp_dir();
+	} elseif(isset($_ENV['TMP'])) {
+		$sysTmp = $_ENV['TMP'];
+	} else {
+		$tmpFile = tempnam('adfadsfdas','');
+		unlink($tmpFile);
+		$sysTmp = dirname($tmpFile);
+	}
+	return $sysTmp;
+}
+
+/**
+ * Returns the temporary folder that sapphire/silverstripe should use for its cache files
+ * This is loaded into the TEMP_FOLDER define on start up
+ *
+ * @param $base The base path to use as the basis for the temp folder name.  Defaults to BASE_PATH,
+ * which is usually fine; however, the $base argument can be used to help test.
+ */
+function getTempFolder($base = null) {
+	if(!$base) $base = BASE_PATH;
+
+	if($base) {
+		$cachefolder = "silverstripe-cache" . str_replace(array(' ', "/", ":", "\\"), "-", $base);
+	} else {
+		$cachefolder = "silverstripe-cache";
+	}
+
+	$ssTmp = BASE_PATH . "/silverstripe-cache";
+	if(@file_exists($ssTmp)) {
+		return $ssTmp;
+	}
+
+	$sysTmp = getSysTempDir();
+	$worked = true;
+	$ssTmp = "$sysTmp/$cachefolder";
+
+	if(!@file_exists($ssTmp)) {
+		@$worked = mkdir($ssTmp);
+	}
+
+	if(!$worked) {
+		$ssTmp = BASE_PATH . "/silverstripe-cache";
+		$worked = true;
+		if(!@file_exists($ssTmp)) {
+			@$worked = mkdir($ssTmp);
+		}
+	}
+
+	if(!$worked) {
+		user_error("Permission problem gaining access to a temp folder. " .
+		"Please create a folder named silverstripe-cache in the base folder "  .
+		"of the installation and ensure it has the correct permissions", E_USER_ERROR);
+	}
+
+	return $ssTmp;
+}
diff --git a/core/startup/ErrorControlChain.php b/core/startup/ErrorControlChain.php
new file mode 100644
index 000000000..9cd344ee0
--- /dev/null
+++ b/core/startup/ErrorControlChain.php
@@ -0,0 +1,121 @@
+<?php
+
+/**
+ * Class ErrorControlChain
+ *
+ * Runs a set of steps, optionally suppressing (but recording) any errors (even fatal ones) that occur in each step.
+ * If an error does occur, subsequent steps are normally skipped, but can optionally be run anyway
+ *
+ * Normal errors are suppressed even past the end of the chain. Fatal errors are only suppressed until the end
+ * of the chain - the request will then die silently.
+ *
+ * The exception is if an error occurs and BASE_URL is not yet set - in that case the error is never suppressed.
+ *
+ * Usage:
+ *
+ * $chain = new ErrorControlChain();
+ * $chain->then($callback1)->then($callback2)->then(true, $callback3)->execute();
+ *
+ * WARNING: This class is experimental and designed specifically for use pre-startup in main.php
+ * It will likely be heavily refactored before the release of 3.2
+ */
+class ErrorControlChain {
+	protected $error = false;
+	protected $steps = array();
+
+	protected $suppression = true;
+
+	/** We can't unregister_shutdown_function, so this acts as a flag to enable handling */
+	protected $handleFatalErrors = false;
+
+	public function hasErrored() {
+		return $this->error;
+	}
+
+	public function setErrored($error) {
+		$this->error = (bool)$error;
+	}
+
+	public function setSuppression($suppression) {
+		$this->suppression = (bool)$suppression;
+	}
+
+	/**
+	 * Add this callback to the chain of callbacks to call along with the state
+	 * that $error must be in this point in the chain for the callback to be called
+	 *
+	 * @param $callback - The callback to call
+	 * @param $onErrorState - false if only call if no errors yet, true if only call if already errors, null for either
+	 * @return $this
+	 */
+	public function then($callback, $onErrorState = false) {
+		$this->steps[] = array(
+			'callback' => $callback,
+			'onErrorState' => $onErrorState
+		);
+		return $this;
+	}
+
+	public function thenWhileGood($callback) {
+		return $this->then($callback, false);
+	}
+
+	public function thenIfErrored($callback) {
+		return $this->then($callback, true);
+	}
+
+	public function thenAlways($callback) {
+		return $this->then($callback, null);
+	}
+
+	public function handleError() {
+		if ($this->suppression && defined('BASE_URL')) throw new Exception('Generic Error');
+		else return false;
+	}
+
+	protected function lastErrorWasFatal() {
+		$error = error_get_last();
+		return $error && $error['type'] == 1;
+	}
+
+	public function handleFatalError() {
+		if ($this->handleFatalErrors && $this->suppression && defined('BASE_URL')) {
+			if ($this->lastErrorWasFatal()) {
+				ob_clean();
+				$this->error = true;
+				$this->step();
+			}
+		}
+	}
+
+	public function execute() {
+		set_error_handler(array($this, 'handleError'), error_reporting());
+		register_shutdown_function(array($this, 'handleFatalError'));
+		$this->handleFatalErrors = true;
+
+		$this->step();
+	}
+
+	protected function step() {
+		if ($this->steps) {
+			$step = array_shift($this->steps);
+
+			if ($step['onErrorState'] === null || $step['onErrorState'] === $this->error) {
+				try {
+					call_user_func($step['callback'], $this);
+				}
+				catch (Exception $e) {
+					if ($this->suppression && defined('BASE_URL')) $this->error = true;
+					else throw $e;
+				}
+			}
+
+			$this->step();
+		}
+		else {
+			// Now clean up
+			$this->handleFatalErrors = false;
+			restore_error_handler();
+		}
+	}
+}
diff --git a/core/startup/ParameterConfirmationToken.php b/core/startup/ParameterConfirmationToken.php
new file mode 100644
index 000000000..cc47bc2bb
--- /dev/null
+++ b/core/startup/ParameterConfirmationToken.php
@@ -0,0 +1,113 @@
+<?php
+
+/**
+ * Class ParameterConfirmationToken
+ *
+ * When you need to use a dangerous GET parameter that needs to be set before core/Core.php is
+ * established, this class takes care of allowing some other code of confirming the parameter,
+ * by generating a one-time-use token & redirecting with that token included in the redirected URL
+ *
+ * WARNING: This class is experimental and designed specifically for use pre-startup in main.php
+ * It will likely be heavily refactored before the release of 3.2
+ */
+class ParameterConfirmationToken {
+	protected $parameterName = null;
+	protected $parameter = null;
+	protected $token = null;
+
+	protected function pathForToken($token) {
+		if (defined('BASE_PATH')) {
+			$basepath = BASE_PATH;
+		}
+		else {
+			$basepath = rtrim(dirname(dirname(dirname(dirname(__FILE__)))), DIRECTORY_SEPARATOR);
+		}
+
+		require_once('core/TempPath.php');
+		$tempfolder = getTempFolder($basepath ? $basepath : DIRECTORY_SEPARATOR);
+
+		return $tempfolder.'/token_'.preg_replace('/[^a-z0-9]+/', '', $token);
+	}
+
+	protected function genToken() {
+		// Generate a new random token (as random as possible)
+		require_once('security/RandomGenerator.php');
+		$rg = new RandomGenerator();
+		$token = $rg->randomToken('md5');
+
+		// Store a file in the session save path (safer than /tmp, as open_basedir might limit that)
+		file_put_contents($this->pathForToken($token), $token);
+
+		return $token;
+	}
+
+	protected function checkToken($token) {
+		$file = $this->pathForToken($token);
+		$content = null;
+
+		if (file_exists($file)) {
+			$content = file_get_contents($file);
+			unlink($file);
+		}
+
+		return $content == $token;
+	}
+
+	public function __construct($parameterName) {
+		// Store the parameter name
+		$this->parameterName = $parameterName;
+		// Store the parameter value
+		$this->parameter = isset($_GET[$parameterName]) ? $_GET[$parameterName] : null;
+		// Store the token
+		$this->token = isset($_GET[$parameterName.'token']) ? $_GET[$parameterName.'token'] : null;
+
+		// If a token was provided, but isn't valid, just throw a 403
+		if ($this->token && (!$this->checkToken($this->token))) {
+			header("HTTP/1.0 403 Forbidden", true, 403);
+			die;
+		}
+	}
+
+	public function parameterProvided() {
+		return $this->parameter !== null;
+	}
+
+	public function tokenProvided() {
+		return $this->token !== null;
+	}
+
+	public function params() {
+		return array(
+			$this->parameterName => $this->parameter,
+			$this->parameterName.'token' => $this->genToken()
+		);
+	}
+
+	public function reloadWithToken() {
+		global $url;
+
+		// Are we http or https?
+		$proto = 'http';
+
+		if(isset($_SERVER['HTTP_X_FORWARDED_PROTOCOL'])) {
+			if(strtolower($_SERVER['HTTP_X_FORWARDED_PROTOCOL']) == 'https') $proto = 'https';
+		}
+
+		if((!empty($_SERVER['HTTPS']) && $_SERVER['HTTPS'] != 'off')) $proto = 'https';
+		if(isset($_SERVER['SSL'])) $proto = 'https';
+
+		// What's our host
+		$host = $_SERVER['HTTP_HOST'];
+
+		// What's our GET params (ensuring they include the original parameter + a new token)
+		$params = array_merge($_GET, $this->params());
+		unset($params['url']);
+
+		// Join them all together into the original URL
+		$location = "$proto://" . $host . BASE_URL . $url . ($params ? '?'.http_build_query($params) : '');
+
+		// And redirect
+		header('location: '.$location, true, 302);
+		die;
+	}
+}
diff --git a/docs/en/changelogs/2.4.11.md b/docs/en/changelogs/2.4.11.md
new file mode 100644
index 000000000..3fd3f5e19
--- /dev/null
+++ b/docs/en/changelogs/2.4.11.md
@@ -0,0 +1,23 @@
+# 2.4.11 (Not yet released)
+
+## Overview
+
+ * Security: Require ADMIN for `?flush=1` (stop denial of service attacks)
+ ([#1692](https://github.com/silverstripe/silverstripe-framework/issues/1692))
+
+## Details
+
+### Security: Require ADMIN for ?flush=1 and ?flush=all
+
+Flushing the various manifests (class, template, config) is performed through a GET
+parameter (`flush=1`). Since this action requires more server resources than normal requests,
+it can facilitate [denial-of-service attacks](https://en.wikipedia.org/wiki/Denial-of-service_attack).
+
+To prevent this, main.php now checks and only allows the flush parameter in the following cases:
+
+ * The [environment](/topics/environment-management) is in "dev mode"
+ * A user is logged in with ADMIN permissions
+ * An error occurs during startup
+
+This applies to both `flush=1` and `flush=all`but only through web requests made through main.php - CLI requests,
+or any other request that goes through a custom start up script will still process all flush requests as normal.
diff --git a/main.php b/main.php
index 85de63abe..91cc90a6e 100644
--- a/main.php
+++ b/main.php
@@ -54,55 +54,129 @@ if(version_compare(phpversion(), 5, '<')) {
  * @see Director::direct()
  */
 
+require_once('core/startup/ErrorControlChain.php');
+require_once('core/startup/ParameterConfirmationToken.php');
 
-/**
- * Include Sapphire's core code
- */
-require_once("core/Core.php");
+class SilverStripeMain {
+	static $token;
 
-if (function_exists('mb_http_output')) {
-	mb_http_output('UTF-8');
-	mb_internal_encoding('UTF-8');
-}
+	static function filterFlush($chain) {
+		self::$token = new ParameterConfirmationToken('flush');
 
-Session::start();
-
-// IIS will sometimes generate this.
-if(!empty($_SERVER['HTTP_X_ORIGINAL_URL'])) {
-	$_SERVER['REQUEST_URI'] = $_SERVER['HTTP_X_ORIGINAL_URL'];
-}
-
-// Apache rewrite rules use this
-if (isset($_GET['url'])) {
-	$url = $_GET['url'];
-	// IIS includes get variables in url
-	$i = strpos($url, '?');
-	if($i !== false) {
-		$url = substr($url, 0, $i);
+		if (isset($_GET['flush']) && !self::$token->tokenProvided()) {
+			unset($_GET['flush']);
+		}
+		else {
+			$chain->setSuppression(false);
+		}
 	}
-	
-// Lighttpd uses this
-} else {
-	if(strpos($_SERVER['REQUEST_URI'],'?') !== false) {
-		list($url, $query) = explode('?', $_SERVER['REQUEST_URI'], 2);
-		parse_str($query, $_GET);
-		if ($_GET) $_REQUEST = array_merge((array)$_REQUEST, (array)$_GET);
-	} else {
-		$url = $_SERVER["REQUEST_URI"];
+
+	static function includeCore() {
+		/**
+		 * Include Sapphire's core code
+		 */
+		require_once("core/Core.php");
+
+		if (function_exists('mb_http_output')) {
+			mb_http_output('UTF-8');
+			mb_internal_encoding('UTF-8');
+		}
+
+		Session::start();
+	}
+
+	static function parseURL() {
+		global $url;
+
+		// IIS will sometimes generate this.
+		if(!empty($_SERVER['HTTP_X_ORIGINAL_URL'])) {
+			$_SERVER['REQUEST_URI'] = $_SERVER['HTTP_X_ORIGINAL_URL'];
+		}
+
+		// Apache rewrite rules use this
+		if (isset($_GET['url'])) {
+			$url = $_GET['url'];
+			// IIS includes get variables in url
+			$i = strpos($url, '?');
+			if($i !== false) {
+				$url = substr($url, 0, $i);
+			}
+
+		// Lighttpd uses this
+		} else {
+			if(strpos($_SERVER['REQUEST_URI'],'?') !== false) {
+				list($url, $query) = explode('?', $_SERVER['REQUEST_URI'], 2);
+				parse_str($query, $_GET);
+				if ($_GET) $_REQUEST = array_merge((array)$_REQUEST, (array)$_GET);
+			} else {
+				$url = $_SERVER["REQUEST_URI"];
+			}
+		}
+
+		// Remove base folders from the URL if webroot is hosted in a subfolder
+		if (substr(strtolower($url), 0, strlen(BASE_URL)) == strtolower(BASE_URL)) $url = substr($url, strlen(BASE_URL));
+	}
+
+	static function startupDatabase() {
+		if (isset($_GET['debug_profile'])) {
+			Profiler::init();
+			Profiler::mark('all_execution');
+			Profiler::mark('main.php init');
+		}
+
+		// Connect to database
+		require_once("core/model/DB.php");
+		global $databaseConfig;
+
+		if (isset($_GET['debug_profile'])) Profiler::mark('DB::connect');
+		if ($databaseConfig) DB::connect($databaseConfig);
+		if (isset($_GET['debug_profile'])) Profiler::unmark('DB::connect');
+	}
+
+	static function flushIfAllowed() {
+		if (self::$token->parameterProvided() && !self::$token->tokenProvided()) {
+			// First, check if we're in dev mode, or the database doesn't have any security data
+			$canFlush = Director::isDev() || !Security::database_is_ready();
+
+			// Otherwise, we start up the session if needed, then check for admin
+			if (!$canFlush) {
+				if(!isset($_SESSION) && (isset($_COOKIE[session_name()]) || isset($_REQUEST[session_name()]))) {
+					Session::start();
+				}
+
+				if (Permission::check('ADMIN')) {
+					$canFlush = true;
+				}
+				else {
+					$loginPage = Director::absoluteURL(Config::inst()->get('Security', 'login_url'));
+					$loginPage .= "?BackURL=" . urlencode($_SERVER['REQUEST_URI']);
+
+					header('location: '.$loginPage, true, 302);
+					die;
+				}
+			}
+
+			// And if we can flush, reload with an authority token
+			if ($canFlush) self::$token->reloadWithToken();
+		}
+	}
+
+	static function flushIfErrored() {
+		if (self::$token->parameterProvided() && !self::$token->tokenProvided()) {
+			self::$token->reloadWithToken();
+		}
 	}
 }
 
-// Remove base folders from the URL if webroot is hosted in a subfolder
-if (substr(strtolower($url), 0, strlen(BASE_URL)) == strtolower(BASE_URL)) $url = substr($url, strlen(BASE_URL));
-
-if (isset($_GET['debug_profile'])) {
-	Profiler::init();
-	Profiler::mark('all_execution');
-	Profiler::mark('main.php init');
-}
-
-// Connect to database
-require_once("core/model/DB.php");
+$chain = new ErrorControlChain();
+$chain
+	->then(array('SilverStripeMain', 'filterFlush'))
+	->then(array('SilverStripeMain', 'includeCore'))
+	->thenAlways(array('SilverStripeMain', 'parseURL'))
+	->then(array('SilverStripeMain', 'startupDatabase'))
+	->then(array('SilverStripeMain', 'flushIfAllowed'))
+	->thenIfErrored(array('SilverStripeMain', 'flushIfErrored'))
+	->execute();
 
 // Redirect to the installer if no database is selected
 if(!isset($databaseConfig) || !isset($databaseConfig['database']) || !$databaseConfig['database']) {
@@ -117,10 +191,6 @@ if(!isset($databaseConfig) || !isset($databaseConfig['database']) || !$databaseC
 	die();
 }
 
-if (isset($_GET['debug_profile'])) Profiler::mark('DB::connect');
-DB::connect($databaseConfig);
-if (isset($_GET['debug_profile'])) Profiler::unmark('DB::connect');
-
 if (isset($_GET['debug_profile'])) Profiler::unmark('main.php init');
 
 // Direct away - this is the "main" function, that hands control to the appropriate controller