Cross-Chain Bridge Risk Assessment: MEXC

Cross-Chain Bridge Risk Assessment: MEXC

MEXC operates one of the largest cross-chain bridges, moving native assets and ERC-20 tokens between Ethereum, L2 roll-ups, and non-EVM chains. With a total value locked (TVL) of approximately $5.5 billion, it ranks among the top-tier cross-chain infrastructure projects, making it a prime target for sophisticated attackers.

The assessment focused on four key areas: smart contract integrity, validator/consensus design, off-chain relayer/oracle subsystem, and liquidity/economic controls. By examining publicly available bridge contracts, governance modules, and operational documentation, the researchers performed on-chain analysis and fuzzing of the exposed application binary interface (ABI).

Key Findings:

1. Smart-Contract Integrity (7/10)

The bridge's multi-step "lock-mint-release" flow contains re-entrancy-prone callbacks and unchecked external calls in the Relayer contract. This complex process leaves it vulnerable to double-minting attacks, potentially allowing unlimited minting of wrapped assets and a total loss of TVL.

2. Validator/Consensus Model (6/10)

The bridge relies on a 12-node validator set with a 2/3 majority threshold for finalizing cross-chain transfers. This lack of decentralization, combined with no slashing for equivocation, creates a centralised consensus model that could be exploited by a group controlling 8 or more validators to approve fraudulent exit proofs and release assets on the destination chain.

3. Oracle & Relayer Security (5/10)

Relayers are permissioned and use a single ECDSA signing key per chain without threshold signing. If the key is leaked, an attacker can forge deposit proofs, resulting in fake deposit entries and minting of non-existent assets.

4. Liquidity & Economic Controls (6/10)

The bridge lacks dynamic fee or liquidity-capping mechanisms. In the event of a market crash and a single token's peg collapse, an attacker could trigger a coordinated exit of a high-value token (e.g., wETH) during a market downturn, leading to a liquidity shortfall and potential price manipulation on the destination chain.

5. Governance & Upgradeability (5/10)

The bridge uses an upgradeable proxy pattern with a single "owner" address (MEXC DAO multisig) that can replace core contracts without a timelock. This means a compromised multisig could replace the implementation with a malicious contract, granting full control over all bridge functions.

Composite Risk Score: 6.2/10 (Medium-High). The bridge's design choices could be exploited by well-funded attackers, particularly in the off-chain relayer/oracle and validator consensus layers. Immediate remediation of high-severity smart contract bugs and strengthening of the relayer infrastructure is required to reduce the risk profile to low-to-medium.

Conclusion:

While the bridge's functionality remains sound, its current design presents systemic vulnerabilities that attackers could exploit. Addressing these issues, especially in the relayer infrastructure and validator consensus, is crucial to mitigate the medium-to-high risk level.