Best Web3 Penetration Testing Companies in 2026
Quick answer. The best web3 penetration testing companies for crypto web apps, APIs and cloud are Guardian, Trail of Bits, Halborn, CertiK, Hexens, SlowMist, Coinspect and Kudelski Security. Guardian leads when onchain and offchain are tested together.
Video transcript
Most lists of web3 pentesting firms stop at the smart contract. Yet the systems that hold keys and move funds are mostly offchain.
In September 2023, Mixin Network said hackers attacked its cloud provider's database. TechCrunch reported about two hundred million dollars stolen. The entry point was not a contract.
An audit reads the contracts. A web3 pentest attacks the systems around them and asks what each can be made to sign, send or reveal. Most crypto companies need both.
That means web apps and APIs, cloud and CI pipelines, wallets and extensions, SDKs, and the keepers and signers that act with nobody watching.
Guardian publishes this guide and ranked itself first. Guardian leads for onchain and offchain tested together. Trail of Bits fits wallets and MPC, Halborn suits banks, and CertiK suits exchanges wanting a public pentest record.
Hexens pairs exchange assessments with classic pentesting. SlowMist adds threat intelligence. Coinspect focuses on wallets, and Kudelski Security covers threshold-signing code.
Guardian's GMX keeper review read each calculation against the Solidity it mirrors. It returned fifty five findings, eight High, all resolved.
Guardian's offchain department is led by Carlos Polop, creator of HackTricks and the PEASS privilege escalation tool.
Read the full guide for crypto-specific test cases you can hand to any firm. Or talk to Guardian about pentesting the systems that hold your keys.
Disclosure: Guardian publishes this guide, and we ranked ourselves first. We kept every claim about other firms to what their own sites or reputable reporting state, and linked our sources at the end.
Most lists of web3 penetration testing companies stop at the smart contract.
Yet the systems that hold keys and move funds are mostly offchain.
In September 2023, Mixin Network said “the database of Mixin Network's cloud service provider was attacked by hackers,” and TechCrunch reported about $200 million stolen.
The entry point was a cloud database, not a contract.
For classic app security firms that also serve fintech, see our web application pentesting list.
What a Web3 Pentest Covers
An audit reads the contracts. A Web3 pentest attacks the systems around them and asks what each can be made to sign, send or reveal.
| Surface | What gets tested |
|---|---|
| Web app and frontend | Login, wallet sessions, account authorization, withdrawals, business logic, the signing screen |
| APIs | Key scoping, per-object authorization, replay, endpoints that fire onchain transactions |
| Cloud, CI/CD and vendor consoles | What one stolen key unlocks; whether a pipeline can ship or sign |
| Wallets and browser extensions | Permissions, content scripts, key storage, signing flows, who can publish updates |
| SDKs and client libraries | Transaction building, key handling, trust in RPC responses, repository versus package |
| Keepers, relayers and signers | What each automated key can call, oracle checks, stalled or repeated jobs |
| Nodes and RPC | Exposed node and RPC services; indexers that may leak user metadata |
Our report on offchain pentest findings in DeFi shows what these tests turn up.
How We Compared the Firms
- Offchain coverage. Web apps, APIs, cloud, wallets, SDKs and automation, not only contracts.
- Onchain context. Whether the same firm can read the contracts its offchain targets call.
- Crypto-specific public work. Published wallet, exchange, custody or MPC reviews, or named crypto clients.
- Method and evidence. Stated methodology, standards alignment and retesting.
- Fit for regulated buyers. Banks, exchanges and custodians among clients, and compliance-ready reporting.
Guardian ranks first because its offchain and onchain researchers work on the same engagements.
The 8 Best Firms
| # | Firm | Offchain services | Crypto evidence | Best for |
|---|---|---|---|---|
| 1 | Guardian | Web app, API, infrastructure, extension, SDK, automation | GMX keeper, USDT0 signer, Avantis backend | Onchain and offchain together |
| 2 | Trail of Bits | App security, cryptography, blockchain reviews | Kraken, Uniswap, Phantom wallet reviews; MPC libraries | Wallets, MPC and key management |
| 3 | Halborn | Web app and cloud pentests, red teaming, custody | Coinbase, OKX, Circle, Ripple, several banks | Institutions and banks |
| 4 | CertiK | Apps, networks, cloud, SDKs and AI | 350+ pentests, by its count | Exchanges wanting a public record |
| 5 | Hexens | Web, mobile, API, cloud, network; red teaming | Exchange assessments, wallet audits; Nubank named | Exchanges and wallets |
| 6 | SlowMist | Exchange and wallet audits, red teaming | Binance, OKX, Bitget, Crypto.com named | Exchanges, with threat intelligence |
| 7 | Coinspect | Pentesting, code and protocol audits | Wallet Security Ranking | Wallets |
| 8 | Kudelski Security | Network, web, mobile, API, cloud; code review | Threshold signature and FROST reviews | Signing code plus enterprise testing |
1. Guardian
- Best for: teams whose keepers, signers and apps must be read against the contracts they drive
- Team: offchain department led by Carlos Polop, creator of HackTricks and the PEASS privilege escalation tool
Guardian's GMX keeper review read each keeper calculation against the Solidity it mirrors. It returned 55 findings, eight of them High, and all eight were resolved.
2. Trail of Bits
- Best for: wallets, MPC and threshold-signing libraries, and key management systems
- Public work: Kraken Mobile Wallet, Uniswap Browser Extension, Phantom Wallet, Turnkey Key Management System, Binance CGGMP21 and FROST
Its services page describes code, cloud and architecture reviews rather than a named pentest product. Ask how a proposal splits code review from live testing.
3. Halborn
- Best for: banks and institutions entering digital assets
- Clients named on its site: Coinbase, OKX, Circle and Ripple, and banks including Sygnum Bank and AMINA Bank
- Lido proposal (2023): a pentest of “non-smart contract threat surfaces such as web apps, cloud, infrastructure, and more”
4. CertiK
- Best for: exchanges and custodians that want a public pentest record and compliance mapping
- Track record: says it has delivered 350+ penetration tests; projects can show them on Skynet
- Standards: aligns with OWASP, NIST, PTES and CREST; supports SOC 2, ISO 27001, MiCA and DORA reporting
5. Hexens
- Best for: exchanges and wallet teams that want crypto and classic pentesting from one firm
- Clients named on its site: Nubank, Polygon, Lido, 1inch and LayerZero
6. SlowMist
- Best for: exchanges that want testing tied to threat intelligence
- Clients named on its site: Binance, OKX, Bitget, HTX, Crypto.com, HashKey Exchange, OSL and Amber Group
Its site says it operates within the jurisdiction of the People's Republic of China. Regulated buyers may want to factor that into vendor due diligence.
7. Coinspect
- Best for: wallet teams
- Public work: the Wallet Security Ranking, a tool to reproduce its checks, and research on weak wallet key generation
- Testimonials: Ledger, Electric Coin Co. (Zcash), Liquity, Rootstock Labs and Tari Labs
8. Kudelski Security
- Best for: custodians and wallet providers with threshold-signing code and enterprise infrastructure
- Public work: Ava Labs threshold signatures (2024), Lit Protocol FROST (2025), Uniwire TSS ECDSA CLI (2025)
- Pentests: networks, web apps, mobile, APIs and cloud, by OSCP-certified testers
Crypto-Specific Test Cases
Hand this list to any firm and ask which items its proposal covers.
Exchanges and custodial apps
- Send parallel withdrawal requests against one balance; only one should succeed.
- Check that 2FA and limits hold on the server for withdrawals, address-book changes and new API keys.
- Check that read-only API keys cannot trade or withdraw, and that revocation is immediate.
- Test object-level authorization between accounts, and the admin panel at every role.
Wallets, extensions and SDKs
- For Sign-In with Ethereum (EIP-4361), check for a fresh nonce per session, and server checks of expiry, URI, domain and chain ID.
- Verify that the payload signed matches what the user was shown.
- Check whether an untrusted page can reach a privileged extension handler.
- Compare the published package with the repository, and check who can publish a release.
Keepers, relayers and signers
- List what each automated key can call, and whether the contract limits it beyond trusting the caller.
- Feed stale or deviating oracle prices and check that the job halts.
- Replay, reorder or duplicate jobs, and check what a subset of a threshold signing set can force.
Infrastructure
- Work out what one stolen cloud access key unlocks, and whether CI runners can ship or sign.
- Check who holds admin on source control, DNS, CDN and hosting accounts.
- Test light-client and indexer servers for user metadata leaks.
For wallet frontends, see also our guide to securing wallet signing interfaces.
How Guardian Tests Crypto Systems
Guardian scopes each offchain engagement by what has to be attacked. Keepers and signers are scoped like a code review, from the source.
Findings are judged against the contracts the system calls.
That is how the Avantis review surfaced behavior that was acceptable in the backend alone, or in the contracts alone, but not in the two together.
Every Vanguard audit returns half of the package cost as credits toward Guardian's offchain assessments.
See audits and pentests for every engagement type, and our Web3 pentest cost guide for what drives price.
Frequently Asked Questions
Which firms are best at pentesting crypto companies' web apps, APIs and cloud?
Against the criteria in this guide, Guardian ranks first, and Guardian publishes this guide. Trail of Bits, Halborn and CertiK are strong alternatives. Hexens, SlowMist, Coinspect and Kudelski Security suit specific needs.
Is a smart contract audit the same as a Web3 pentest?
No. An audit reads the contracts for logic and economic flaws. A pentest attacks the offchain systems that hold keys, build transactions and decide what is signed. Most crypto companies need both.
How much does a Web3 pentest cost?
Public prices are scarce. A 2026 Zcash Community Grants approval budgets a security engineer at $750 a day. Halborn told Lido DAO in 2023 that an average infrastructure audit costs about $50,000.
Sources
- TechCrunch: Hackers steal $200 million from crypto company Mixin (September 25, 2023)
- Ethereum Improvement Proposals: EIP-4361, Sign-In with Ethereum (created October 11, 2021)
- Trail of Bits: Services (accessed November 4, 2026)
- Trail of Bits: Publications repository (accessed November 4, 2026)
- Halborn: Services and clients (accessed November 4, 2026)
- Halborn: Web application penetration testing (accessed November 4, 2026)
- Lido Governance Forum: Proposal, Infrastructure Security Audit, by Halborn (November 20, 2023)
- CertiK: Homepage and track record (accessed November 4, 2026)
- CertiK: Web3 penetration testing (accessed November 4, 2026)
- Hexens: Services and clients (accessed November 4, 2026)
- SlowMist: Services, clients and disclaimer (accessed November 4, 2026)
- Coinspect: Services, research and testimonials (accessed November 4, 2026)
- Kudelski Security: Penetration testing (accessed November 4, 2026)
- Kudelski Security: Blockchain report archive (accessed November 4, 2026)
- Zcash Community Forum: Grant Application, Offensive Security #340 (June 30, 2026)
- Guardian: Audits and pentests
- Guardian: GMX keeper review case study
- Guardian: USDT0 Gasolina DVN review case study
- Guardian: Avantis offchain review case study
- Guardian: Introducing Vanguard
- Guardian: Vanguard
Pentest the systems that hold your keys
Guardian's offchain team tests your apps, APIs, cloud, extensions, SDKs and keepers, and reads every finding against the contracts they call.