What are basic secure coding practices?

Question

IT Interview Practice · Accepted Answer

**Secure coding** means writing code that resists attacks and protects data — following practices that prevent common vulnerabilities. Understanding the basics helps developers build security in from the start rather than bolting it on later.

## Core secure coding practices

```text
✓ VALIDATE all input (never trust user/external input); allowlist where possible
✓ Use PARAMETERIZED queries (prevent SQL injection); ESCAPE output (prevent XSS)
✓ AUTHENTICATE and AUTHORIZE properly (verify identity; check permissions server-side)
✓ HANDLE SENSITIVE DATA carefully — hash passwords, encrypt sensitive data, use HTTPS
✓ Don't HARDCODE SECRETS (keys, passwords) in code → use env vars / secrets managers
✓ Use SECURE DEFAULTS; fail securely (errors shouldn't expose data or grant access)
```

## Avoid common mistakes

```text
✗ Trusting user input / client-side checks (validate on the SERVER)
✗ Exposing sensitive info in errors/logs (stack traces, secrets, PII)
✗ Using outdated/vulnerable DEPENDENCIES (keep them updated; scan them)
✗ Rolling your own CRYPTO (use vetted libraries/standards, not custom algorithms)
✗ Overly broad permissions (apply LEAST PRIVILEGE)
```

## Security principles

```text
✓ LEAST PRIVILEGE → grant only the minimum access needed (limit damage)
✓ DEFENSE IN DEPTH → multiple layers (no single point of failure)
✓ FAIL SECURELY → on error, default to denying access / safe state
✓ KEEP IT SIMPLE → complex code hides bugs/vulnerabilities
✓ SECURITY BY DESIGN → build it in from the start (shift left), not as an afterthought
```

## Why it matters

Understanding basic secure coding practices is foundational because **developers write the code that is secure or vulnerable**, so applying secure practices is essential for building safe software, making this important security knowledge.

Secure coding — writing code that resists attacks and protects data — is increasingly a core developer responsibility, and understanding the basics enables building security in from the start.

The **core practices** — validating input (never trusting external input), using parameterized queries (preventing SQL injection) and escaping output (preventing XSS), proper authentication and authorization (server-side), handling sensitive data carefully (hashing passwords, encryption, HTTPS), **not hardcoding secrets** (using environment variables or secrets managers — a common mistake), and using secure defaults that fail securely — directly prevent the most common vulnerabilities.

Understanding the **common mistakes to avoid** — trusting client-side checks, exposing sensitive info in errors and logs, using outdated/vulnerable dependencies, **rolling your own crypto** (a notorious mistake — using vetted libraries instead), and overly broad permissions — helps developers steer clear of frequent security errors.

Understanding the **security principles** — **least privilege** (minimum necessary access, limiting damage), **defense in depth** (multiple layers, no single point of failure), **failing securely** (defaulting to denied access on error), keeping it simple (complexity hides vulnerabilities), and **security by design** (building it in from the start) — provides the mindset and framework that underlies all secure coding.

These principles and practices reflect how security-conscious developers work.

Since developers write the code that determines whether software is secure, and since applying basic secure coding practices (input validation, parameterized queries, proper auth, secret management) and principles (least privilege, defense in depth, security by design) prevents common vulnerabilities, and since understanding these is essential for building safe software, understanding basic secure coding practices is foundational, essential security knowledge — the practices and principles that enable developers to build security into their code, increasingly expected of all developers, and central to producing software that protects its users and data.

Core secure coding practices

Avoid common mistakes

Security principles

Why it matters

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