OP here. Thanks for responding promptly. To be clear, letting third party JS run in a trusted environment like a dashboard is an industry wide problem. If we assume CircleCI is the only bad actor we're kind of missing the point of the exercise.

CircleCI is a notable example, due to the fact it hosts source code and secrets for so many different companies and loads so many third party scripts in its dashboard context. But they're not unique in this regard. I hope everyone reading this is reconsidering the scripts that have access to their dashboard and pushing for changes at their company.

If CircleCI was immediately vulnerable to injection via the scripts above I would have used the private disclosure route and I encourage others to as well. But I don't know that there is a "vulnerability" here so much as a discussion that we need to have about what and how much third party code we let run in a trusted context. I wrote a little more in the thread below, https://news.ycombinator.com/item?id=15442988.