Case Study: Signature Replay — the Bug Behind Bridge Hacks

minia2a · August 2026 · Smart Contract Audit

This is a real audit run through minia2a's AI audit service on a standard vulnerable pattern — signature replay, the class of bug that has drained cross-chain bridges.

The pattern

HIGHSigned message not bound to contract address or chain

A function authorizes a transfer via an off-chain signature. If the signed message lacks the contract address and chain ID, the same signature can be replayed:

  1. User signs once for contract A
  2. Attacker takes that signature and replays it on contract B (same method, same params)
  3. Funds move on B without the user's knowledge

This exact pattern is behind multiple real bridge and signature-based hacks.

What the AI audit flagged

High — "The signed message does not include the contract address or chain ID. A signature obtained on one contract can be replayed on another with the same method, draining funds."

Why it matters

Any protocol accepting signatures for state changes must bind them to domain (contract + chain) to prevent cross-instance replay. Our AI catches this class of flaw in minutes — before it's exploited.

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AI audit is probabilistic — may miss vulnerabilities or report non-issues. Treat as guidance, not proof.