Dangerous default: auto_accept_shared_attachments

[nate-selzer]

Found a bug? Maybe our Slack Community can help.

Describe the Bug

By default, this module deploys a transit gateway that automatically accepts any vpc attachment requests. I believe this default is dangerous, because if an attacker knows your account ID and tgw id, they can send an attachment request and have access to your network.

Expected Behavior

I think this model should instead use the aws_ec2_transit_gateway_vpc_attachment_accepter terraform resource to accept the attachment request, and have the default be to disable automatic attachments.

Steps to Reproduce

Steps to reproduce the behavior:

1. Deploy a transit gateway.
2. From a theoretical attackers account, initiate a peering request
3. The peering request is automatically accepted

Screenshots

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Environment (please complete the following information):

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Additional Context

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