Add an upper bound to the POST data SecurityComponent will consider.

'Kurita Takashi' has let us know that the previous patterns could be
abused by an evil doer. One could potentially send a very large deeply
nested POST data structure. Matching that structure could overflow the
PCRE limits causing a segmentation fault. Adding an upper bound will
solve the problem and I doubt anyone is doing POST data structures with
more than 10 levels of nesting.

lib/Cake/Controller/Component/SecurityComponent.php

@@ -470,8 +470,8 @@ protected function _validatePost(Controller $controller) {
 		$multi = array();
 
 		foreach ($fieldList as $i => $key) {
-			if (preg_match('/(\.\d+)+$/', $key)) {
-				$multi[$i] = preg_replace('/(\.\d+)+$/', '', $key);
+			if (preg_match('/(\.\d{1,10})+$/', $key)) {
+				$multi[$i] = preg_replace('/(\.\d{1,10})+$/', '', $key);
 				unset($fieldList[$i]);
 			}
 		}