What Is the Primary Attack Vector for a Pure Proof-of-Stake Network?

The primary attack vector is the 51% attack, also known as the majority attack. An attacker who controls 51% or more of the total staked cryptocurrency can gain control over the network's consensus process.

This allows them to censor transactions, prevent honest block finalization, and potentially double-spend by validating their own malicious chain. The economic cost is the price of acquiring and staking the necessary tokens.