Understanding OWASP Top 10: A Beginner's Breakdown

If you're new to web security, the OWASP Top 10 is where you should start. Published by the Open Web Application Security Project, this list represents the most critical security risks facing web applications. It's updated periodically based on real-world data from security assessments, bug bounties, and breach reports.

Think of the OWASP Top 10 as your curriculum. Master these ten categories, and you'll understand the vulnerabilities behind the vast majority of web security breaches. Let's break down each one in plain language.

A01:2021 - Broken Access Control

What it is: Users can access data or perform actions they shouldn't be able to. Imagine logging into a bank and being able to see someone else's account by changing the account number in the URL.

Real example: An e-commerce site lets you view your orders at /orders/12345. By changing to /orders/12346, you can see another customer's order details including their address and what they bought.

Why it's #1: It moved from #5 to #1 in the 2021 update because it's incredibly common and easy to exploit. Developers often forget to verify that users have permission to access specific resources.

A02:2021 - Cryptographic Failures

What it is: Sensitive data isn't properly protected. This includes transmitting data without encryption, storing passwords in plain text, or using weak cryptographic algorithms.

Real example: A healthcare app stores patient social security numbers in the database without encryption. When the database is breached, attackers get immediate access to all SSNs.

What to look for: HTTP instead of HTTPS, MD5 or SHA1 for password hashing, hardcoded encryption keys, or sensitive data in logs.

A03:2021 - Injection

What it is: User input is sent to an interpreter (database, OS, etc.) without proper validation. The classic example is SQL injection, where an attacker can execute arbitrary database commands.

Real example: A login form sends your username directly to the database. An attacker enters: admin'-- as the username. This comments out the password check, logging them in as admin.

Types of injection: SQL injection, NoSQL injection, Command injection, LDAP injection, XPath injection. The principle is the same: untrusted data being interpreted as commands.

A04:2021 - Insecure Design

What it is: Security problems baked into the application's architecture. Unlike other categories that are implementation bugs, insecure design means the system was conceived without security in mind.

Real example: A password reset feature emails a link that never expires. An attacker who gains access to old emails can reset passwords indefinitely.

How to address it: Threat modeling during design, security requirements in specifications, and secure design patterns from the start.

A05:2021 - Security Misconfiguration

What it is: Improperly configured security settings. Default credentials left unchanged, unnecessary features enabled, detailed error messages exposed, or missing security headers.

Real example: A development server is deployed to production with debug mode enabled. Error pages now show full stack traces, database connection strings, and internal file paths.

Common misconfigs: Default admin passwords, exposed admin panels, directory listing enabled, missing HTTPS, permissive CORS policies.

A06:2021 - Vulnerable and Outdated Components

What it is: Using libraries, frameworks, or other software with known vulnerabilities. This is the supply chain problem: your code might be secure, but your dependencies aren't.

Real example: The Log4j vulnerability (Log4Shell) in 2021 affected millions of applications because Log4j is used everywhere. Attackers could execute code remotely on any system using vulnerable versions.

Prevention: Regular dependency updates, automated vulnerability scanning (Dependabot, Snyk), and knowing what components you're using.

A07:2021 - Identification and Authentication Failures

What it is: Weaknesses in how users prove their identity. Weak password requirements, missing brute-force protection, improper session management, or credential stuffing vulnerabilities.

Real example: A site allows unlimited login attempts. An attacker runs through lists of common passwords until they find one that works. Or session tokens don't expire after logout, allowing session hijacking.

Best practices: Multi-factor authentication, rate limiting, strong password policies, secure session management, and credential breach detection.

A08:2021 - Software and Data Integrity Failures

What it is: Failing to verify that software updates, critical data, or CI/CD pipelines haven't been tampered with. This includes insecure deserialization and software supply chain attacks.

Real example: The SolarWinds attack in 2020: attackers compromised the build system and injected malicious code into a legitimate software update. Thousands of organizations installed the trojanized update.

Prevention: Code signing, checksum verification, secure CI/CD pipelines, and careful vetting of dependencies.

A09:2021 - Security Logging and Monitoring Failures

What it is: Insufficient logging to detect attacks, missing monitoring to alert on suspicious activity, or logs that don't capture the right information.

Why it matters: The average time to detect a breach is 200+ days. Without proper logging and monitoring, attackers can operate undetected for months, exfiltrating data at leisure.

What to log: Authentication events (success and failure), authorization failures, input validation failures, and any security-relevant actions.

A10:2021 - Server-Side Request Forgery (SSRF)

What it is: Tricking the server into making requests to unintended locations. This can expose internal services, bypass firewalls, or access cloud metadata endpoints.

Real example: A feature that fetches a URL and displays its content. An attacker provides http://169.254.169.254/latest/meta-data/ (AWS metadata endpoint) and retrieves cloud credentials.

Prevention: Validate and sanitize all URLs, use allowlists for permitted destinations, block requests to internal IP ranges.

Where's XSS?

You might notice Cross-Site Scripting (XSS) isn't its own category anymore. In 2021, it was merged into A03: Injection, since XSS is essentially HTML/JavaScript injection. It's still one of the most common vulnerabilities—just categorized differently.

Your Learning Path

Start with the top three: Broken Access Control, Cryptographic Failures, and Injection. These are the most impactful and the most commonly exploited. Once you're comfortable identifying and understanding these, work your way down the list.

For each category, try to find at least three real-world examples from breach reports or CVE databases. Understanding how these vulnerabilities manifest in production systems is more valuable than memorizing definitions.

Ready to practice? AliceSec offers hands-on challenges for every OWASP Top 10 category. Start with our beginner-friendly exercises and work your way up to advanced scenarios.