I agree with James that Moodle has excellent SQLi protections.
There are different types of threats which can be used to take advantage of your network security vulnerability.
Besides SQL Injection there are threats like unauthorized data access, penetration testing and many more.
My advice would be to perform network security testing to validate that your network is secure.
You can do it with a tool like BreakingPoint. It simulates your environments and injects security attacks and malware into the simulated traffic to test the resiliency of your network security.