This wasn't a flaw with Ethereum itself or its protocol, but rather an issue with one of the its client implementations (go-ethereum), other clients like Parity, Harmony, etc.. are unaffected.
This statement from ethereum/geth developer Felix Lange even hedges on how completely the vulnerability has been mitigated, which may not bode well for ethereum in general:
>We have done our best to mitigate the attacks within the limits of the protocol. The paper is concerned with 'low-resource' eclipse attacks. As far as we know, the bar has been raised high enough that eclipse attacks are not feasible without more substantial resources...
He did go on to mention his belief alternative ethereum client Parity isn't vulnerable, so there's that at least.
When people majorly botch x509 cert validation because the spec is so monstrously complex that's still a problem with x509.