Shadow Fork Swapback: Deferred Finality Exploits in Interoperable Blockchain Systems

Cross-chain interoperability protocols rely on assumptions of transaction finality to enable asset transfers, message passing, and state mirroring across heterogeneous blockchains. However, finality in many blockchain systems is probabilistic, delayed, or context-dependent.This paper introduces Shadow Fork Swapback, a class of cross-chain exploits in which an attacker leverages temporary or private forks on a source chain to trigger asset transfers across interoperable systems, then abandons the fork before deep finality is reached. The destination chain retains the effects of the transaction, while the originating chain reverts the state, creating asymmetric finality. We analyze the structural preconditions, execution patterns, and systemic risks of this exploit, demonstrating that it represents a fundamental interoperability failure rather than an implementation bug.