Code Audits
Blockchain Bridge Audit
Secure your cross-chain infrastructure before vulnerabilities cost you millions. At Three Sigma, our blockchain bridge audits deliver a complete review of your protocol’s design, code, and validator processes to reduce the risk of exploits that could halt interoperability or drain locked assets.
100+
audits
completed
$8.2B
in client assets protected
$183.2B
in transacted value secured
300+
crit / high issues found
Consolidated clients
Blockchain security company with
3+ years of expertise
We combine expert manual analysis with advanced tooling to evaluate bridge security from end to end, covering smart contracts, relayers, message verification, and custody logic, so you can launch and operate with confidence.
What is a Blockchain Bridge Audit?
A blockchain bridge audit is a specialized security review designed to identify vulnerabilities in systems that transfer assets or data between different blockchains. Bridges are a critical piece of cross-chain infrastructure, but they are also one of the most targeted components in the blockchain ecosystem. The irreversible nature of blockchain transactions means that a single exploit can drain funds permanently. At Three Sigma, we deliver in-depth bridge security audits to ensure your cross-chain operations are secure, efficient, and resistant to known attack vectors.
Why a Blockchain Bridge Audit Matter
Bridges often hold or control significant amounts of locked value, making them high-value targets for attackers. Many of the largest exploits in blockchain history have involved bridges, resulting in losses of hundreds of millions of dollars. While traditional smart contract audits cover core code vulnerabilities, a cross chain bridge audit focuses on securing the locking, minting, verification, and messaging processes unique to cross-chain systems. It ensures that all participating chains, smart contracts, and relayer mechanisms work reliably under both normal and adversarial conditions.
Our Approach to Bridge Auditing
We start by mapping the entire bridge architecture, including smart contracts, off-chain relayers, validation logic, and asset custody mechanisms. We analyze each interaction point between chains to ensure messages are verified correctly and assets are only minted or released when conditions are met.
We test both optimistic and zero-knowledge-based bridges, checking cryptographic proofs, validator sets, and fraud detection systems. Where applicable, we also assess the bridge’s governance and upgradeability controls to prevent abuse.
For teams with broader needs we also perform:
Common Issues Found in Bridge Audits
Weak or Incomplete Message Verification
Occurs when cross-chain messages lack rigorous proof validation, allowing forged or altered data to be accepted. This can lead to unauthorized asset releases, replay attacks, or inconsistent states across blockchains.
Insecure Validator Selection
Bridges relying on a small validator set risk collusion, compromised keys, or Sybil attacks. Without robust rotation, slashing, and quorum rules, attackers can bypass consensus and seize locked funds.
Replayable Transactions
Happens when valid cross-chain transactions can be resent on other networks without detection. This flaw may duplicate assets, disrupt supply integrity, or drain liquidity pools in connected ecosystems.
Edge Case Handling Failures
Occurs when bridges mismanage rare conditions such as timeouts/expirations, malformed or out-of-order messages, reorg/finality differences, or orphaned transfers This can cause asset loss, transfer freezes, or unexpected settlement mismatches.
Custody Contract Vulnerabilities
Weaknesses in bridge asset-locking contracts may allow unauthorized withdrawals or bypass withdrawal limits. Exploitable flaws in upgradeability, access control, or withdrawal logic can result in permanent fund loss.
Typical vulnerabilities in bridges include weak or incomplete message verification, insecure validator selection, replayable transactions, and incorrect handling of edge cases in cross-chain transfers. Flaws in custody contracts can allow unauthorized withdrawals, while poor timeout handling may result in stuck assets. Bridges that rely on a small set of validators are especially vulnerable to collusion attacks, making early security prioritization essential for long-term resilience.
Real-World Examples
Common real-world bridge exploits highlight the critical need for thorough blockchain bridge audits. Issues such as flawed proof verification can enable forged transfer messages, while compromised validator keys may result in the loss of all locked assets. In many cases, a cross chain bridge audit could have detected these weaknesses early, preventing replay attacks, duplicated asset creation, and large-scale fund losses.
Our Bridge Audit Process
Scoping and planning
We define all bridge components, chains involved, and verification processes.
Architecture review
We map the full cross-chain design, trust boundaries, and message/asset flows, including validator/threshold assumptions and upgrade/governance controls.
Code review
We inspect all smart contracts and relayer code for logic flaws and security issues.
Testing
Static analysis, property-based fuzzing and invariants, and mainnet-fork simulations; we build PoCs to reproduce issues and measure real-world impact.
Reporting and recommendations
We provide an audit report and step-by-step remediation guidance.
Verification
We assist your team with the fixes to confirm all issues are resolved.
Hear from our Clients
Deliverables You Can Expect
Check out our previous case studies and their reports, with all identified vulnerabilities, severity ratings, and clear remediation guidance. This includes both on-chain and off-chain findings relevant to your blockchain bridge audit, covering smart contracts, relayers, and cross-chain communication logic.
Post-audit support is included
to help your team implement changes and verify their effectiveness through re-testing.
What You Gain
from a Three Sigma Audit
Our blockchain bridge security audit is more than a checkmark on your roadmap, it’s an investment in your project’s success.
Prevent costly exploits before they impact your users.
Increase trust with investors, partners, and the Web3 community.
Accelerate compliance with evolving blockchain security standards.
Protect brand reputation in an industry where trust is currency.
Industries We Secure
Our audits have helped secure decentralized applications across multiple verticals.
DeFi
Lending platforms, DEXs, and staking protocols.
NFT & Collectibles
Marketplaces, launchpads, and minting platforms.
Gaming & Metaverse
Play-to-earn games, asset trading hubs, and immersive experiences.
Cross-Chain Infrastructure
Bridges, oracles, and interoperability layers.
Frequent answers and questions
Check out the Blockchain Bridge Audit F.A.Q.
Why do I need a blockchain bridge audit?
Bridges are among the most exploited components in Web3. A blockchain bridge audit ensures secure cross-chain transfers, protects locked assets, and mitigates validator or relayer vulnerabilities.
Do you audit both smart contracts and off-chain components?
Yes. Our multi-chain bridge audit examines smart contracts, validator logic, relayer code, proof verification, and operational security to identify risks across the full bridge architecture.
What are the most common vulnerabilities found in blockchain bridges?
A thorough cross chain bridge audit often reveals issues such as flawed proof verification, validator collusion, insecure message-passing, replay attacks, and weak liquidity protection mechanisms.
Can you audit bridges across multiple blockchain ecosystems?
Absolutely. Our expertise covers cross chain bridge audits for Ethereum, Solana, Aptos, Sui, BNB Chain, Avalanche, and other ecosystems, ensuring end-to-end security.
How does a blockchain bridge audit improve protocol trust?
By validating bridge logic, verifying security assumptions, and ensuring consistency across connected chains, a blockchain bridge audit builds confidence for users, partners, and liquidity providers.