Security of Cross-chain Bridges: Attack Surfaces, Defenses, and Open Problems
Mengya Zhang, Xiaokuan Zhang, Yinqian Zhang, Zhiqiang Lin
Abstract
Cross-chain bridges play a pivotal role in enabling token and data exchanges between disparate blockchains. Despite their growing popularity, these bridges are still in their infancy and have been the target of numerous attacks, leading to significant financial losses. Current literature lacks a comprehensive examination of the security landscape surrounding cross-chain bridges, with existing incident reports dispersed and unconsolidated. Addressing this gap, this paper presents a systematic investigation into the security challenges facing cross-chain bridges. We begin by outlining the key features of current cross-chain bridges, including their applications, verification processes, communication models, and a novel threefold categorization. From this foundation, we identify 12 potential attack vectors and develop a taxonomy of cross-chain bridge attacks observed over the past three years, classifying them into 10 unique categories. Each category is detailed with corresponding vulnerabilities, illustrated through Solidity code examples. Furthermore, we explore existing defense mechanisms, propose potential security solutions, and highlight crucial open questions and avenues for future research. This paper aims to illuminate the path towards more secure cross-chain bridge designs and stimulate further investigation into fortifying the cross-chain bridge ecosystem.