OWASP Top 10 Explained: Security Risks Every Developer Should Know

The OWASP Top 10 represents the most critical security risks facing web applications today. Understanding these vulnerabilities is essential for any developer building software that handles user data or connects to the internet.

What is OWASP?

The Open Web Application Security Project (OWASP) is a nonprofit foundation that works to improve software security. Their Top 10 list, updated periodically based on real-world data, has become the de facto standard for web application security awareness.

The 2021 OWASP Top 10

1. Broken Access Control

Previously at #5, broken access control moved to the top spot. This vulnerability occurs when users can act outside their intended permissions.

Examples:

• Accessing another user's account by modifying URL parameters
• Viewing or editing someone else's data
• Accessing admin panels as a regular user
• API endpoints missing proper authorization checks

Prevention:

• Implement role-based access control (RBAC)
• Deny by default for all resources
• Log access control failures and alert on repeated failures
• Invalidate session tokens after logout

2. Cryptographic Failures

Previously called "Sensitive Data Exposure," this category covers failures related to cryptography that often lead to data exposure.

Common issues:

• Transmitting data in clear text (HTTP, FTP, SMTP)
• Using old or weak cryptographic algorithms
• Using default crypto keys or weak keys
• Not enforcing encryption in transit

Prevention:

• Use TLS everywhere with modern cipher suites
• Encrypt all sensitive data at rest
• Use strong adaptive hashing functions (Argon2, bcrypt) for passwords
• Avoid deprecated cryptographic functions

3. Injection

Injection vulnerabilities occur when untrusted data is sent to an interpreter as part of a command or query. SQL injection is the most famous, but injection affects NoSQL, OS commands, LDAP, and more.

Prevention:

• Use parameterized queries / prepared statements
• Use ORMs (but understand their limitations)
• Validate and sanitize all input
• Escape special characters when dynamic queries are unavoidable

4. Insecure Design

New to the 2021 list, this focuses on design and architectural flaws. No amount of good implementation can fix an insecure design.

Examples:

• Recovering passwords via security questions
• Unlimited trust in user input
• Missing rate limiting on sensitive operations

Prevention:

• Threat modeling during design phase
• Use secure design patterns
• Write security stories alongside features
• Integration security testing

5. Security Misconfiguration

This remains one of the most commonly seen issues. It includes missing security hardening, misconfigured permissions, and unnecessary features enabled.

Common issues:

• Default credentials unchanged
• Error messages revealing stack traces
• Unnecessary features enabled (ports, services, accounts)
• Missing security headers

Prevention:

• Automated hardening processes
• Minimal platforms without unnecessary features
• Review configurations in all environments
• Regular security audits

6. Vulnerable and Outdated Components

Using components with known vulnerabilities exposes your application to attacks that often have ready-made exploits.

Prevention:

• Regularly audit dependencies
• Use tools like Dependabot, Snyk, or npm audit
• Subscribe to security bulletins
• Remove unused dependencies

7. Identification and Authentication Failures

Formerly "Broken Authentication," this covers flaws in confirming user identity and session management.

Common issues:

• Permitting weak passwords
• Missing or ineffective multi-factor authentication
• Session fixation vulnerabilities
• URLs containing session IDs

Prevention:

• Implement MFA where possible
• Enforce strong password policies
• Use secure session management
• Implement account lockout with delays

8. Software and Data Integrity Failures

New in 2021, this covers assumptions about software updates, critical data, and CI/CD pipelines without verifying integrity.

Examples:

• Auto-updating without verifying signatures
• Insecure deserialization
• CI/CD pipeline vulnerabilities

Prevention:

• Verify digital signatures on updates
• Use dependency verification
• Secure your CI/CD pipeline
• Review code and configuration changes

9. Security Logging and Monitoring Failures

Insufficient logging and monitoring allows breaches to go undetected and attackers to persist in systems.

What to log:

• Login attempts (success and failure)
• Access control failures
• Input validation failures
• High-value transactions

Prevention:

• Ensure logs capture sufficient context
• Use centralized log management
• Establish alerting thresholds
• Create incident response plans

10. Server-Side Request Forgery (SSRF)

SSRF occurs when a web application fetches a remote resource without validating the user-supplied URL. This can allow attackers to access internal services.

Prevention:

• Sanitize and validate all client-supplied input
• Use allowlists for remote resources
• Disable HTTP redirections
• Don't send raw responses to clients

Applying OWASP in Your Development Process

Security isn't a one-time activity. Build these practices into your workflow:

1. Training: Ensure all developers understand these vulnerabilities
2. Code Review: Include security checks in review process
3. Testing: Use both automated tools and manual penetration testing
4. Monitoring: Continuously watch for signs of attack
5. Updates: Keep dependencies and infrastructure current

Conclusion

The OWASP Top 10 provides a practical starting point for web application security. While it doesn't cover everything, addressing these ten categories significantly reduces your attack surface. Make security a continuous priority, not an afterthought.