Nigerian Fintech Security — Fixing Webhook Bypass, Race Conditions & Amount Manipulation
Nigerian fintech platforms face a unique attack surface — the vulnerabilities here don't just expose data, they enable direct financial theft. Here are the three most critical issues and how to fix them. 1. Pay
Nigerian fintech platforms face a unique attack surface — the vulnerabilities here don't just expose data, they enable direct financial theft. Here are the three most critical issues and how to fix them.
1. Paystack Webhook Bypass
// VULNERABLE — no verification
app.post('/webhook/paystack', async (req, res) => {
if (req.body.event === 'charge.success') {
await creditWallet(req.body.data.metadata.userId,
req.body.data.amount / 100);
}
res.sendStatus(200);
});
// SECURE — verify signature
app.post('/webhook/paystack',
express.raw({ type: 'application/json' }),
async (req, res) => {
const hash = crypto
.createHmac('sha512', process.env.PAYSTACK_SECRET)
.update(req.body)
.digest('hex');
if (hash !== req.headers['x-paystack-signature']) {
return res.status(401).send('Invalid signature');
}
const event = JSON.parse(req.body);
if (event.event === 'charge.success') {
await creditWallet(event.data.metadata.userId,
event.data.amount / 100);
}
res.sendStatus(200);
}
);
2. Race Condition in Balance Updates
// VULNERABLE — race condition allows double withdrawal
const user = await User.findByPk(userId);
if (user.balance < amount) throw new Error('Insufficient');
await User.update({ balance: user.balance - amount }, { where: { id: userId } });
// SECURE — atomic update with row locking
const transaction = await db.transaction({
isolationLevel: Transaction.ISOLATION_LEVELS.SERIALIZABLE
});
try {
const user = await User.findByPk(userId, {
lock: transaction.LOCK.UPDATE,
transaction
});
if (!user || user.balance < amount) {
await transaction.rollback();
throw new Error('Insufficient funds');
}
await User.update(
{ balance: db.literal(`balance - ${amount}`) },
{ where: { id: userId, balance: { [Op.gte]: amount } }, transaction }
);
await transaction.commit();
} catch (err) {
await transaction.rollback();
throw err;
}
3. Server-Side Amount Validation
// VULNERABLE — trusting client amount
app.post('/api/purchase', async (req, res) => {
const { productId, amount } = req.body; // Never trust this amount
await processPayment(req.user.id, amount);
});
// SECURE — validate against database
app.post('/api/purchase', async (req, res) => {
const { productId } = req.body;
const product = await Product.findByPk(productId);
// Use the server's amount — not the client's
await processPayment(req.user.id, product.price);
});
The Pattern
All three vulnerabilities share a common root: trusting external input without verification. Webhooks must be signed. Balances must be locked. Amounts must be server-validated. None of these are complex fixes — but all three are commonly missing in Nigerian fintech codebases.
ZikarelHub LTD is Nigeria's #1 software and digital agency — secure fintech built from the ground up.
What fintech security issues have you encountered in Nigerian products? 👇
Originally published by Dev.to Security. Aggregated on AIWithGhost for educational purposes — full credit and traffic to the original publisher.