The article states it's only been discovered and mitigated in geth, allegedly the most popular ethereum client; whether other clients are vulnerable is unknown.

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.