Web Application Security Essentials Every Developer Should Know
Web Application Security Essentials Every Developer Should Know
You write the code that accepts requests, touches a database, and returns responses. That makes web application security your direct responsibility from the first commit.
Start by treating every piece of incoming data as untrusted. Then layer on controls for authentication, sessions, and output.
Run These Checks on Every Feature
- Validate and sanitize inputs at the edge. Reject anything that does not match the expected format before it reaches business logic.
- Use parameterized queries for every database call. String concatenation is the fastest way to open a door for SQL injection.
- Escape output based on context. HTML-encode content that lands inside templates, and JSON-encode values that go into script blocks.
- Store session tokens in HTTP-only, secure cookies and regenerate the token after login or privilege changes.
- Enforce HTTPS with HSTS and set strict content security policy headers that block inline scripts and third-party domains you do not control.
Here is a quick comparison of common patterns you will see in real code reviews.
| Pattern | Example | Fix |
|---|---|---|
| Direct string insert | “SELECT * FROM users WHERE id = ” + userId | Prepared statement with placeholder |
| Inline script echo | <script>var data = <%= userInput %>;</script> | JSON.stringify then textContent assignment |
| Plain cookie | document.cookie = “session=abc123” | Set cookie with HttpOnly; Secure; SameSite=Strict |
Run these five items on the next pull request that touches user data. The fixes are small, but they close the gaps that show up in production logs within weeks.