Revert guest checkout account registration problem introduced by patch SUPEE-10570. Note: this does not protect against security issues related to session lifetime.

invalid_session_fix.patch

diff --git a/app/code/core/Mage/Core/Model/Session/Abstract/Varien.php b/app/code/core/Mage/Core/Model/Session/Abstract/Varien.php
index 59b3ea8..35155f1 100644
--- a/app/code/core/Mage/Core/Model/Session/Abstract/Varien.php
+++ b/app/code/core/Mage/Core/Model/Session/Abstract/Varien.php
@@ -485,7 +485,7 @@ class Mage_Core_Model_Session_Abstract_Varien extends Varien_Object
             && isset($validatorData[self::VALIDATOR_PASSWORD_CREATE_TIMESTAMP])
             && isset($sessionData[self::VALIDATOR_SESSION_EXPIRE_TIMESTAMP])
             && $validatorData[self::VALIDATOR_PASSWORD_CREATE_TIMESTAMP]
-            > $sessionData[self::VALIDATOR_SESSION_EXPIRE_TIMESTAMP] - $this->getCookie()->getLifetime()
+            > $sessionData[self::VALIDATOR_SESSION_EXPIRE_TIMESTAMP]
         ) {
             return false;
         }