Flat-fee security audits for x402 integrations, gateway routes, and the contracts behind them, in three tiers from three thousand dollars.
x402 lets agents pay per API call in stablecoins, and the protocol has stabilized at v2 under the Linux Foundation while real money already moves across the network. The flip side is that every new x402 service inherits the security surface of HTTP, on-chain settlement, agent identity, and signed-payment verification all at once. A single missing nonce check, a poorly handled facilitator response, or a misconfigured CAIP-2 network is the kind of bug that drains a wallet in production.
We audit x402 integrations with three tools we own. Our security lab models twelve attack archetypes against working exploits and patches, our hss-sniffer static analyzer scans contracts against those archetypes alongside the Slither rule set and maps every finding to a remediation walkthrough, and we operate BitBooth, a multi-chain x402 gateway running in production on Base mainnet settling real USDC through the Coinbase CDP Facilitator. Because we run the surface ourselves, we know which classes of bug actually happen and which are only theoretical.
Each tier is flat-fee with a written delivery date. No hourly creep, and no surprise invoices.
Six areas mapped against the x402 v2 spec, our twelve-archetype security lab, and what we have learned running BitBooth in production.
402 challenge construction, accepts array correctness, payment-header schema validation, expiry handling, and replay protection through a nonce store and idempotency keys.
Per-chain adapter correctness across Base, XRPL, Solana, and Stellar, with confirmation depth, payTo validation, amount-base-unit handling, network mismatch detection, and CAIP-2 parsing.
Reentrancy, access control, signature replay, oracle manipulation, share inflation, delegatecall storage collision, unchecked external calls, and the rest of the twelve archetypes from our security lab.
Agent wallet provisioning, hot wallet exposure, KMS and Secrets Manager handling, multi-sig requirements for high-value routes, and a key rotation runbook.
Per-tenant rate limiting, fraud event tracking, route-level configuration injection, multi-tenant data leakage, and billing edge cases.
Webhook delivery dead-letter queues, RPC failover, facilitator availability, observability gaps, incident response readiness, and rollback paths.
Every tool we use is open source or our own, so the work stays public and auditable with no black boxes.
A sanitized example pulled from our security lab fixtures.
The enforceX402 handler validates the payment-header schema and the on-chain transaction reference, but it does not check the nonce against a seen-nonces store before accepting the payment. An attacker can replay a previously confirmed payment to repeatedly access the same paid resource without sending new on-chain payments.
// Before
const verify = await adapter.verifyPayment({ txHash, expectedTo, ... })
if (verify.ok) return resource
// After
const seen = await nonceStore.has(payment.nonce)
if (seen) throw new ReplayError("nonce already used")
const verify = await adapter.verifyPayment(...)
if (verify.ok) {
await nonceStore.put(payment.nonce, ttl)
return resource
}
Recommended fix. Wire a TTL-bounded nonce store backed by DynamoDB, Redis, or Postgres into the verify path, and reject any payment whose nonce has been seen within the payment-window seconds. The same idempotency pattern guards every paid route on BitBooth.
We do not audit a surface we have never shipped. Every claim below maps to production code or a public registration record you can read before you hire us.
Self-review your x402 integration before you book an audit. It covers nonce replay, settlement verification, wallet exposure, tenant isolation, and twenty-one more checks. Free, email-gated, and no obligation.