If there is an update for a security vulnerability your Developer Portal will prompt a message on the Status report page.
If you are an on-prem customer you will need to follow the steps listed on this doc page.
http://apigee.com/docs/developer-services/content/upgrading-drupal-opdk-installation
If you are a cloud customer you will need to accept the updates on your pantheon dashboard.
Here is the pantheon document explaining the same https://pantheon.io/docs/articles/sites/code/applying-upstream-updates/
If you need access to the pantheon dashboard please open a support ticket.
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