In the GitFlops: The Dangers of Terraform Automation Platforms article Elliot Ward highlights how Terraform automation platforms can be exploited to compromise cloud environments.

In particular it looks at how to exploit the terraform plan phase to execute commands and gain access to cloud infrastructure credentials.
In combination with a classic GitOps flow, where unprivileged users can open pull-requests and terraform plan is run on these pull-requests, this creates privilege escalation vulnerabilities putting the cloud infrastructure at risk.

In terms of preventing this, the recommendation is to validate Terraform config before running terraform plan on it.
One tool mentioned in the article that can be used to for this validation is Conftest.

A month ago, Elliot also presented the topic at the BSides Bern conference.
The slides of the presentation have been made available by the conference, here is a copy.