MyCI is meant as a personal CI with mostly local access. But that doesn't mean there can't be potential security threats that you need to be aware of.

When adding a new test to your system from a submodule, make sure you trust the source. These tests will run on your target devices and if they were malicious can try to take advantage for example from running on a rooted device to try to get access to your internal network and potentially steal some data.

Especially if you allow access through the internet!

For both running Jenkins server and for your target devices you want to run tests on. The less privilege the user has, the less likely any harm is done if the user was compromised.