OWASP Top 10 Security Vulnerabilities

Expert guidance for identifying, preventing, and remediating the most critical web application security risks based on OWASP Top 10 2021.

When to Use This Skill

• •Conducting security audits and code reviews
• •Implementing secure coding practices in new features
• •Reviewing authentication and authorization systems
• •Assessing input validation and sanitization
• •Evaluating third-party dependencies for vulnerabilities
• •Designing security controls and defense-in-depth strategies
• •Preparing for security certifications or compliance audits
• •Investigating security incidents or suspicious behavior

OWASP Top 10 2021 Overview

Ranked by Risk Severity:

1. •A01 - Broken Access Control (↑ from #5)
2. •A02 - Cryptographic Failures (formerly Sensitive Data Exposure)
3. •A03 - Injection (↓ from #1)
4. •A04 - Insecure Design (NEW)
5. •A05 - Security Misconfiguration
6. •A06 - Vulnerable and Outdated Components
7. •A07 - Identification and Authentication Failures
8. •A08 - Software and Data Integrity Failures (NEW)
9. •A09 - Security Logging and Monitoring Failures
10. •A10 - Server-Side Request Forgery (SSRF) (NEW)

Quick Reference

Load detailed guidance for each vulnerability:

Security Audit Workflow

1. •Identify Scope: Determine application components and attack surface
2. •Select Vulnerabilities: Choose relevant OWASP categories based on features
3. •Load Reference: Read appropriate reference file(s) for detailed patterns
4. •Analyze Code: Review code against vulnerable and secure patterns
5. •Document Findings: Record vulnerabilities with severity and remediation
6. •Verify Fixes: Test that remediations properly address issues
7. •Test Security: Run automated security testing (SAST, DAST, SCA)

Core Security Principles

Defense in Depth

• •Layer security controls at network, application, data, and monitoring levels
• •Ensure failure of one control doesn't compromise entire system

Secure by Default

• •Deny all access by default, explicitly grant permissions
• •Fail securely (errors don't expose sensitive information)
• •Minimize attack surface (disable unused features)
• •Apply least privilege to all accounts and services

Input Validation

• •Validate type, length, format, and allowed values
• •Use allow-lists over deny-lists
• •Sanitize for specific context (SQL, HTML, shell, etc.)
• •Never trust client input

Common Mistakes

1. •Trusting User Input: Always validate and sanitize all user-supplied data
2. •Rolling Your Own Crypto: Use established libraries (bcrypt, AES-256)
3. •Exposing Errors: Log detailed errors internally, show generic messages to users
4. •Missing Authorization: Check permissions on every request, not just UI
5. •Weak Session Management: Use secure, httpOnly, sameSite cookies with HTTPS
6. •Ignoring Dependencies: Regularly audit and update third-party libraries
7. •No Logging: Log security events for detection and incident response
8. •Default Configurations: Harden all systems, disable defaults

Security Testing Tools

SAST (Static): SonarQube, Semgrep, ESLint security plugins DAST (Dynamic): OWASP ZAP, Burp Suite SCA (Dependencies): npm audit, Snyk, Dependabot Secrets Scanning: GitGuardian, TruffleHog Penetration Testing: Metasploit, Kali Linux tools

Resources

• •OWASP Top 10 2021: https://owasp.org/Top10/
• •OWASP Cheat Sheets: https://cheatsheetseries.owasp.org/
• •OWASP ASVS: Application Security Verification Standard
• •CWE Top 25: Common Weakness Enumeration
• •NIST Cybersecurity Framework: https://www.nist.gov/cyberframework
• •CVE Database: https://cve.mitre.org/
• •Snyk Vulnerability DB: https://snyk.io/vuln/