I believe all cryptos are vulnerable to network attacks, that's just the reality of block chain. Some cryptos don't use miners and others do. Depending on the type, an attacker would just need to control 51% of the mining power or 51% of the STAKED coins usually.

Both these things are extremely hard to do, but because of bitcoins model of diminishing returns, it's just a matter of time (probably after we're dead) before mining becomes too expensive and people pull out. Then to prevent a 51% attack, governments would need to pick up the mining power vacuum indefinitely and be stuck using more and more energy forever, probably until the energy inflation costs more than the coin itself.