Stablecoin payment security
Security reviews for stablecoin payments.
If your product accepts or pays out USDC or USDT, most of the risk is in your own backend: the code that decides a payment has arrived and the code that sends money out. I review that code, explain what I find in plain English, and check your fixes once they’re in.
01 · Where it breaks
Ten ways stablecoin integrations lose money.
Stablecoin payments look like card payments with a different API. They aren’t. There is no chargeback, no fraud desk and no undo. These are the failure modes I test for in every review.
- 01
Trusting the token symbol
Anyone can deploy a token called “USDC”. Deposit detection must match the issuer’s contract address on each chain, never the name or symbol.
- 02
Crediting before finality
A transaction seen in a block is not a settled payment. Crediting on first sight lets reorgs and dropped transactions reverse money you already released.
- 03
Unverified or replayable webhooks
If the endpoint that marks an order “paid” doesn’t verify signatures, timestamps and event IDs, anyone with the URL can pay with a curl command.
- 04
Payouts that send twice
A timeout, a retry and a missing idempotency key. On-chain transfers can’t be reversed, so duplicate payouts are simply lost.
- 05
Decimal and rounding errors
USDC uses 6 decimals on most chains; many tokens use 18; bridged variants differ. Floats and hard-coded decimals turn into overpayments.
- 06
Hot-wallet keys in environment variables
A signing key readable by the web app, the CI runner and every engineer is one leaked log away from an empty treasury.
- 07
Address poisoning
Attackers seed your transaction history with lookalike addresses so an operator copies the wrong one into the next payout.
- 08
Wrong-chain deposits
The same address exists on many EVM chains, but your smart-contract wallet may not. Funds sent on the wrong network can be unrecoverable.
- 09
Ledger drift
Internal balances, on-chain balances and provider balances that nobody reconciles daily. Theft and bugs both hide in the gap.
- 10
Ignoring issuer controls
USDC and USDT issuers can freeze addresses. Accepting funds from a flagged address, or holding treasury in one, is an operational and compliance risk.
02 · The review
One fixed-scope review, before you go live.
An application-security review aimed at the code paths that move funds. You get a prioritised report, working fixes, and a re-test once you’ve shipped them.
- Scope
-
- Threat model of your payment flow, from checkout to treasury
- Code review of deposit detection, webhooks, payouts and ledger
- Key management, signer isolation and spend controls
- Provider configuration: Stripe, Circle, Coinbase, Bridge or self-hosted
- Reconciliation and monitoring: what alerts when money goes missing
- You get
- A written report with each finding rated by severity, reproduced, and paired with a concrete fix, plus an executive summary your auditor, investors or bank partner can read.
- I need
- Read access to the relevant repositories, a staging or testnet environment, and a one-hour walkthrough with an engineer. Never production credentials.
- Timeline
- 5 to 10 working days from kickoff to report, depending on scope. Re-test within 30 days of the report.
| Engagement | When | Fixed fee |
|---|---|---|
| Architecture review | Before you build. Threat model and design review of the planned flow. | from $2,500 |
| Integration security review | Before launch. Full review of code, configuration and infrastructure, with re-test. | from $4,500 |
| Ongoing review | After launch. Every change that touches funds, reviewed before it ships. | from $1,500 / mo |
The exact fee is set after the scoping call and agreed in writing before any work starts. No hourly billing.
Payment webhook is accepted without signature verification, so any caller can mark an order as paid.
Impact. The handler parses the JSON body and fulfils the order if status == "succeeded". It never checks the provider’s signature header, so a single unauthenticated request releases goods or credits a balance without payment.
Fix. Verify the signature over the raw request body with the provider’s SDK, reject events older than five minutes, store processed event IDs, and re-fetch the payment from the provider’s API before fulfilment.
03 · How it works
From first call to fixed in about three weeks.
- Day 0
Scoping call
Thirty minutes, free. You walk me through the flow; I tell you honestly whether a review is worth it yet.
- Day 2
Fixed proposal
Scope, fee and dates in writing within two working days. NDA signed before any code is shared.
- Days 3 to 12
Review
Threat model, code and configuration review, testnet reproduction. Critical issues are reported the day I find them.
- Within 30 days
Report and re-test
Report walkthrough with your team, then a re-test of every fix so the report shows them closed.
04 · Fit
Built for teams shipping stablecoin rails, not launching tokens.
- Fintechs adding stablecoin payoutsContractor, payroll or remittance flows moving USDC across borders.
- Platforms accepting stablecoinsStripe or Coinbase acceptance wired into your own orders, balances and ledger.
- Teams running their own walletsDeposit addresses, sweeping, hot and cold wallets, treasury operations.
- Contract-only auditsIf all you need is a Solidity audit, that is a separate De Faveri Consulting engagement.
- Legal opinions and licensingGENIUS Act or MiCA questions belong with counsel.
- Turnkey checkout with no custom codeIf you only flipped a switch in Stripe, you probably don’t need me yet.
05 · Research
Field notes on stablecoin integration security.
Practical write-ups for engineers. No newsletter wall.
06 · About
Federico De Faveri
I’m a cybersecurity and software engineer. I work where application security meets payments engineering: the off-chain code that decides when money has arrived and when it may leave.
I’ve worked in full-stack development, cloud infrastructure, cybersecurity and reverse engineering since 2016. Since 2017 I’ve been fractional CTO of Gamma Communications in New York, where I built and still run Receipt Rewards, the platform behind national promotions for brands like Unilever, Knorr and Fandango. It has checked about 100,000 receipts and taught me what keeping a system that moves real value running for years actually involves.
ClearLedger is the stablecoin practice of De Faveri Consulting, the Miami firm I founded, which has delivered 50+ projects for 35+ companies. You work with me directly: the person on the scoping call is the person who reads your code and writes your report. If the problem is in your Solidity rather than your integration, we audit that too.
07 · Questions
Before you ask.
Do you audit smart contracts?
Yes, through De Faveri Consulting, which offers Solidity smart contract audits as a separate engagement. ClearLedger reviews focus on the off-chain systems that move stablecoins: your backend, webhooks, wallets, keys and ledger. If you deploy your own contracts too, we can scope both together.
Do you need access to production?
No. Read access to the relevant repositories, a staging or testnet environment, and your infrastructure configuration are enough. Production credentials are never required.
Which providers and chains do you cover?
Integrations built on Stripe, Circle, Coinbase, Bridge or self-hosted wallets, on EVM chains such as Ethereum, Base and Polygon, and on Solana. Other chains can be scoped on the call.
Will you sign an NDA?
Yes, before any code is shared. Findings are only ever shared with you.
08 · Start
Tell me what you’re shipping.
Two lines is enough. I reply within one working day with either a time to talk or an honest “you don’t need this yet”.