What Is the Theoretical Attack Vector Remaining in PoA?

The theoretical attack vector remaining in PoA involves a coordinated effort between a majority of the PoW miners and a majority of the PoS stakers. While the PoW cost deters casual attacks, a well-funded, coordinated entity could potentially mine a malicious block template and then ensure it is signed and validated by a majority of the stakers.

This requires significant collusion and economic resources, making it highly improbable but not impossible.