We have recently updated the old base image for our Cloud Formation Templates with a new base image that removes the default public SSH keys present in the machine. In the old templates, these keys get overwritten on first boot with the ones provided by the user, so only the user that launches the server can have access to the machine. However, there is no reason why the default keys need to be present, so we have removed them. If you have launched a BitNami template in the past using Cloud Formation, you may receive a message from Amazon Web Services mentioning that the image contained default SSH keys. Since, as mentioned, those keys are overwritten with yours, there should be no security issue.
Please feel free to contact us if you have additional questions regarding this topic.