The patch breaks backward compatibility in a way that can affect extensions and customizations. Please review this document and test your extensions to determine if you need to make any adjustments.
Patches are available for Magento Enterprise Edition 1.7 and later releases and Magento Community Edition 1.4 and later releases. You can also upgrade to Magento Enterprise Edition 220.127.116.11 or Community Edition 18.104.22.168.
DOWNLOADING THE SECURITY PATCH
To download the patch, choose from the following options:
Partners: Go to the Partner Portal, select Technical Resources and then select Download from the Enterprise Edition panel. Next, navigate to Magento Enterprise Edition > Patches & Support and look for the folder titled “Security Patches – October 2015.”
Enterprise Edition Merchants: Go to My Account, select the Downloads tab, and then navigate to Magento Enterprise Edition > Support Patches. Look for the folder titled “Security Patches – October 2015.” Merchants can also upgrade to Enterprise Edition 22.214.171.124 and receive the security update as part of the core code.
Community Edition Merchants: Patches for earlier versions of Community Edition can be found on the Community Edition download page (look for SUPEE-6788). Merchants can also upgrade to Community Edition 126.96.36.199 and receive the security update as part of the core code.
Hope this information is useful for you! Thanks for reading!