I don't think there is an efficient way to successfully attack an open source project, except you successfully terrorized every person that contributes to BItcoin.

Currently, adoption is slowed down by the scalability problem. But soon it will be solved when the Lightning Network being implemented and used by the mainstream.

Well, Actually there is indeed some weakness in the Bitcoin as stated in https://en.bitcoin.it/wiki/Weaknesses. But Bitcoin is yet still at an early age, constant and rapid development will cover it all gradually.