You ran intentionally adversarial code with WebSphere?

I run intentionally WebSphere security capabilities to contain EAR and WARs into their own little universe, alongside JEE security capabilites and managers.

Everything that Docker sells was already possible with JEE application containers, just Java only.

To be fair, there were a lot of CVEs because part of the sandbox in Java was capabilities-based, and the Achilles' heel of capabilities is that if you can see it, you can use it, and feature factory work has a bad habit of accidentally making things visible by exposing some parent object in an attempt to be helpful.

I did like the permissions inheritance model quite a bit, but the hybrid ACL/capabilities system was always a bit schizophrenic.

Still way less than C based technology, and besides most of them were related to Java Applets, a completely different stack than application containers like WebSphere.

No, it wasn't; you couldn't keep code running in a WAR off the network. For a number of years, practically every sitewide pentest I did was gameovered by SSRF off Java application servers. I never even bothered to figure out how tight the isolation between co-resident applications was on those things.

Sure you can, by packing the network sensitive code into another Java library and using process internal bean calls across domains.

Now if those guys didn't understood the WebSphere capabilities that is another matter.

The idea behind sandboxed execution environments is to make them resilient to insecure application code. You can't address that problem by stipulating that your application is secure!

Neither did I said that, rather that WebSphere does provide the tooling to create such sandboxes, provided one goes through the effort to create the application architecture in a way that those features at put it use.

It doesn't do magic if the users don't bother to use the tools put at their disposal.

This isn't sandboxing at click of button.

See previous comment.