Mh, I have a rather aggressive stance on these kind of incidents, no matter if they are availability or security related. You can fish for them, you can test for them, and there are entire classes of malicious code you cannot find. For everything you do, turing complete code can circumvent it. There's a lot of interesting reading material going on in the space of malware analysis regarding sandbox detection, for example.

So stop worrying. Try to catch as much as feasible before prod. Then focus on detecting, alerting and ending the actual incident. If code causes an incident, it't probably measurable and detectable. And even then you won't be able to catch everything. As long as a server has behavior observable from the internet, it could be exfiltrating data.