The most recent thing I could think of is the paper by cryptography experts from Stanford University on 3 attack vectors on ETH PoS: https://arxiv.org/pdf/2110.10086.pdf
Cost of such attacks is negligible compared to cost of attacking even a low hashrate PoW.

Generally speaking we can name some of the serious PoS attack vectors:
- The adversary who controls a large amount of PoS coin can have a strong control over that network. For example the premined altcoins or cheap coins that could be bought with little amount of money. It is like PoW 51% attack but it doesn't necessarily need 51% of the supply.