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I thought that Java Applets (and maybe flash, I am less familiar) had an advanced security model, but it was exploit after exploit because of the huge attack surfaces?

I suspect you may run into similar sandbox escapes once things are complicated enough. So it seems like a good idea if they can be made bug free, but good luck with that?

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Part of the problem with the Java sandbox is that it was enforced entirely by the VM + the VM is written in C++. The idea is not inherently bad.

It's been a while since I worked in this area but my recollection was that most JVM security issues in this areas were bypasses of the Java Security Manager often by confusing it about code origin. That's all Java code, not C++.

It's been so long I could be remembering incorrectly.

For both Java and .NET, there were actual verification bugs, as well - when bytecode that's not supposed to be valid gets past the verifier and results in e.g. mistyped references (which can then be used for all kinds of creative vtable abuse). Sometimes it can even be a bug in the VM spec itself, because implications of two different features interacting weren't fully considered.

But, yes, we've tried this idea many times now, and it never held up for long.

Maybe the issue was with how powerful and unrestricted reflection was in java before introduction of modules.

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