𝗬𝗼𝘂𝗿 𝗦𝗮𝗮𝗦 𝗜𝘀 𝗟𝗲𝗮𝗸𝗶𝗻𝗴 𝗠𝗼𝗻𝗲𝘆
Most developers ship their SaaS and move on. They treat security as a task for later. They wait for real users or real money to arrive.
Real financial losses often come from simple mistakes. These are not complex hacks. They are logic errors in your code.
Here are four common ways you lose money:
- Race Conditions in Credit Systems You read a user balance, check it, and then write the new balance. If a user sends two requests at the same time, both requests might pass the check before the first one updates the database. You serve two services for the price of one.
The fix: Use atomic database operations. Instead of reading then writing, use a single command to update the balance only if the user has enough credits.
- Trusting Client Input for Identity You take the email address from the request body during checkout. An authenticated user can change that email to someone else's address. This allows them to create billing sessions for wrong accounts or probe your system.
The fix: Never trust identity from the request body. Extract the email from the verified session token on your server.
- Broken Annual Billing Logic Many developers reset user credits by listening to Stripe payment events. This works for monthly plans. It fails for annual plans. Stripe sends one event per year. Your users get credits on day one and nothing for the next eleven months.
The fix: Decouple credit resets from billing events. Use a daily cron job to check which users need a reset based on a reset date.
- Insecure Token Storage You store password reset tokens in localStorage. Any script on your page can access localStorage. This includes browser extensions and third-party analytics.
The fix: Use your authentication SDK to handle recovery tokens. Let the library process the token automatically without storing it in local storage.
The problem is always the same: you trust the client. You trust that requests arrive one at a time. You trust that billing events cover every case.
Fixing these issues takes less than a day. Audit your code before you lose money.
Source: https://dev.to/manolito99/your-saas-is-probably-leaking-money-right-now-and-you-dont-know-it-1g38