★ Default bytes32(0) acceptable as valid root

Evidence summary #

[★ CRITICAL] YELLOW (structural gap, economic mitigation present): HubPool proposeRootBundle() does NOT validate that roots are non-zero; only gate is poolRebalanceLeafCount > 0. MerkleLib verifyRelayerRefund() and verifyV3SlowRelayFulfillment() do NOT check root ≠ bytes32(0) before calling MerkleProof.verify(). However, Across's architecture materially differs from Nomad: (1) proposer must post a WETH bond; (2) ~2h challenge window; (3) any address can dispute, initiating DVM vote that slashes proposer bond. Zero-root bundle would be disputeable and costly. Yellow, not red, because attack requires burning bond and winning DVM vote.

Sources #

Methodology #

Determine whether the bridge inbox accepts a default-value (bytes32(0)) Merkle root as a valid proof root (Nomad bug class).

See the full factor methodology and distribution across all protocols →