Decentralized Finance (DeFi) is a revolutionary breakthrough that is reconditioning the conventional finance space by leveraging transparent, permissionless, and blockchain-enabled services. The emerging blockchains are growing at a high pace in the past couple of years, revealing imperative security and scalibility challenges that may impede their growth and widespread. Our work investigates the security vulnerabilities of DeFi protocols, covering smart contract attacks, oracle attacks, governance attacks, as well as the scalability bottlenecks of network saturation and increasing gas price. We present an extensive review of existing research literature from 2021 to 2025 in order to verify the practicality of the proposed systems, to answer the question whether existing solutions such as layer-2 scaling solutions, cross-chain interaction, and formal verification mechanisms can be practical. The paper also examines the trade-off between decentralization and performance, and points out what it takes to design DeFi ecosystems to be resilient and scalable, providing a roadmap to drive future research. The results will also help to advance the knowledge on how to protect decentralized infrastructure while maintaining high throughput and global reachability.