I don't see how to protect this hypothetical socialist state either. Cuba has managed to escape any attempts that the US has made to overthrow it's democratic mandate but it had the support of the USSR in it's early stages and there's no hegemonic power right now that could be of similar help.
I'm not a particularly bright person, and I don't think I'll ever have a proper answer.
That the USSR managed to last long as long as it did despite being invaded by more developed nations multiple times during the aftermath of its revolution and eventually collapsed largely due to its own internal corruption does put paid to the idea that some authoritarian measures will help protect a socialist state from external attempts to destabilise it.
The problem seems to be one inherent within the structure of states. Any heirarchical structure like that is fit to be abused by someone sufficiently self interested that they'd put their own interests above the interests of the people gestures at Mikhail Gorbachev selling the USSR out to the Western core for his own enrichment.
Anarchism, being decentralised, might be able to withstand some of the issues that were present in the late USSR. But previous anarchist attempts have been crushed by outside actors much easier than socialist attempts.
I don't really know what there is to be done.