Transaction Finality Mismatches

Transaction finality mismatches occur when a protocol assumes a transaction is irreversible on a source chain before the blockchain has reached true probabilistic or absolute finality. In some blockchains, a transaction can appear to be confirmed but is later reversed due to a chain reorganization, where a longer chain replaces the current one.

If a bridge protocol treats such a transaction as final and releases assets on the destination chain, it becomes vulnerable to double-spending attacks. The mismatch arises because different chains have different finality mechanisms and timeframes.

A secure cross-chain protocol must account for the specific finality characteristics of each connected chain, often by requiring a sufficient number of block confirmations before considering a transaction final. Failing to do so creates a systemic risk that can be exploited to drain the bridge's collateral.