The Walls Have Ears: Unveiling Cross-Chain Sandwich Attacks in DeFi

TL;DR

This paper uncovers a new type of cross-chain sandwich attack in DeFi that exploits transaction information leaks to execute profitable front-running strategies, revealing significant vulnerabilities and attack profits.

Contribution

It identifies a critical vulnerability in cross-chain bridge protocols, demonstrating how attackers can exploit emitted events to execute successful sandwich attacks.

Findings

Attackers profited over 5.27 million USD from cross-chain sandwich attacks.

The study shows current defenses are ineffective against this new attack vector.

Empirical analysis used two months of cross-chain data from Symbiosis protocol.

Abstract

Cross-chain interoperability is a core component of modern blockchain infrastructure, enabling seamless asset transfers and composable applications across multiple blockchain ecosystems. However, the transparency of cross-chain messages can inadvertently expose sensitive transaction information, creating opportunities for adversaries to exploit value through manipulation or front-running strategies. In this work, we investigate cross-chain sandwich attacks targeting liquidity pool-based cross-chain bridge protocols. We uncover a critical vulnerability where attackers can exploit events emitted on the source chain to learn transaction details on the destination chain before they appear in the destination chain mempool. This information advantage allows attackers to strategically place front-running and back-running transactions, ensuring that their front-running transactions always precede those of existing MEV bots monitoring the mempool of the destination chain. Moreover, current sandwich-attack defenses are ineffective against this new cross-chain variant. To quantify this threat, we conduct an empirical study using two months (August 10 to October 10, 2025) of cross-chain transaction data from the Symbiosis protocol and a tailored heuristic detection model. Our analysis identifies attacks that collectively garnered over \(5.27\) million USD in profit, equivalent to 1.28\% of the total bridged volume.