This problem arose after upgrading to Magento 18.104.22.168. which is a patch release that patches a number of security flaws in Magento. After installation of the patch some parts of the front-end template stayed blank. Review of the exception.log file shows a number of exceptions that seem to occur from the template filter classes of Magento.
The error is:
exception 'Exception' with message 'Notice: Undefined variable: block in /data/web/public/app/code/core/Mage/Core/Model/Email/Template/Filter.php on line 187' in /data/web/public/app/code/core/Mage/Core/functions.php:245
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Cause of the problem
It is due to the fact that a permission system has been introduces that withholds various template filters from running. Since 22.214.171.124 a so called permission block is added to the filter class ‘Mage_Core_Model_Email_Template_Filter’ which is the class responsible for replacing templates:
If the type is not allowed, the $block variable is not created and an exception is written to the log files.
Magento refers to this patch as:
APPSEC-1057, template processing method allows access to private information.
The permission system normally only allows a reduced number of variables en block types:
enterprise_catalogevent/event_lister (in Magento Enterprise Edition)
The resolution is to add the required template variables and blocks to the permission tables ‘permission_variable’ and ‘permission_block’.
Log-in to your Magento back-end and navigate to System > Permissions > Blocks . Add a new entry and enter the block name (e.g.: mymodule/myblock). Choose Allow and click save.
You could add an SQL insert statement to the upgrade script of your module as well to automate this process when your plugin is updated.
More information about Magento patch SUPEE-6788.