Any security issues should be submitted directly through privately reporting a security vulnerability. In order to determine whether you are dealing with a security issue, ask yourself these two questions:

Can I access something that's not mine, or something I shouldn't have access to?
Can I disable something for other people?

If the answer to either of those two questions are "yes", then you're probably dealing with a security issue. Note that even if you answer "no" to both questions, you may still be dealing with a security issue, so if you're unsure, just follow the instructions linked above.