I suspect that nearly all containerization software is insecure. Especially with timing attacks like side-channel attacks (Row Hammer, etc):
https://en.wikipedia.org/wiki/Timing_attack
https://en.wikipedia.org/wiki/Side-channel_attack
In the end, the only way to "prove" container security is to be able to point to the fact that nobody has broken out of it yet. It's ..remarkable that our entire cloud infrastructure runs on containers that have never been audited by brute-force in this manner.