We identified an issue in the Amazon ECS agent where, under certain conditions, an introspection server could be accessed off-host by another instance if the instances are in the same security group or if their security groups allow incoming connections that include the port where the server is hosted. This issue does not affect instances where the option to allow off-host access to the introspection server is set to 'false'. This issue has been addressed in ECS agent version 1.97.1. We recommend upgrading to the latest version and ensuring any forked or derivative code is patched to incorporate the new fixes. If customers cannot update to the latest AMI, they can modify the Amazon EC2 security groups to restrict incoming access to the introspection server port (51678).

Information Disclosure in Amazon ECS Container Agent