Comprehensive guide to OWASP Top 10 web application security vulnerabilities. Learn about injection attacks, broken authentication, security misconfigurations, and other critical risks threatening modern web applications.

OWASP Top 10: Critical Web Application Security Vulnerabilities in 2025

The Open Web Application Security Project (OWASP) is a nonprofit foundation dedicated to improving software security worldwide. Their flagship project, the OWASP Top 10, represents the most critical security risks to web applications based on data from security firms, bug bounty vendors, and organizations worldwide.

This comprehensive guide covers the current OWASP Top 10 vulnerabilities, providing security professionals with essential knowledge for penetration testing, vulnerability assessment, and secure development practices.

What is OWASP?

OWASP (Open Web Application Security Project) is a global community focused on improving application security. Founded in 2001, OWASP provides:

• Free security tools and resources
• Application security standards and guidelines
• Educational materials and training
• Community-driven research and documentation

The organization operates under an open-source model, making all resources freely available to developers, security professionals, and organizations worldwide.

Understanding the OWASP Top 10

The OWASP Top 10 is updated every 3-4 years based on:

• Data analysis from security firms and organizations
• Community surveys from security professionals
• Real-world vulnerability assessments
• Industry feedback and security research

The current version (2021) reflects the evolving threat landscape and provides a foundation for web application security programs.

OWASP Top 10 Web Vulnerabilities (2021)

A01:2021 – Broken Access Control

Risk Level: Critical

Broken access control vulnerabilities occur when applications fail to properly restrict user access to resources and functions.

Common Attack Scenarios:

• Insecure Direct Object References (IDOR)
• Privilege escalation attacks
• Unauthorized data access
• Administrative function bypass

// Vulnerable: No access control validation
@GetMapping("/api/users/{userId}")
public User getUserDetails(@PathVariable Long userId) {
    return userService.findById(userId);
}

// Secure: Proper access control implementation
@GetMapping("/api/users/{userId}")
public User getUserDetails(@PathVariable Long userId, Principal principal) {
    if (!authService.canAccessUser(principal.getName(), userId)) {
        throw new AccessDeniedException("Unauthorized access");
    }
    return userService.findById(userId);
}

Mitigation Strategies:

• Implement role-based access control (RBAC)
• Deny access by default
• Validate permissions on every request
• Use automated testing for access control rules

A02:2021 – Cryptographic Failures

Risk Level: High

Previously known as “Sensitive Data Exposure,” this category focuses on failures related to cryptography and data protection.

Common Vulnerabilities:

• Weak encryption algorithms
• Insufficient key management
• Missing encryption for sensitive data
• Improper certificate validation

// Vulnerable: Weak encryption implementation
public String encryptPassword(String password) {
    return DigestUtils.md5Hex(password);  // MD5 is cryptographically broken
}

// Secure: Strong encryption with proper salting
public String encryptPassword(String password) {
    BCryptPasswordEncoder encoder = new BCryptPasswordEncoder(12);
    return encoder.encode(password);  // Strong hashing with salt
}

Mitigation Strategies:

• Use strong encryption algorithms (AES-256, RSA-2048+)
• Implement proper key management
• Encrypt data in transit and at rest
• Use established cryptographic libraries

A03:2021 – Injection

Risk Level: Critical

Injection vulnerabilities occur when untrusted data is sent to an interpreter as part of a command or query, potentially leading to code execution.

Types of Injection Attacks:

• SQL Injection
• NoSQL Injection
• OS Command Injection
• LDAP Injection

// Vulnerable: SQL Injection via string concatenation
public User authenticateUser(String username, String password) {
    String query = "SELECT * FROM users WHERE username='" + username + 
                   "' AND password='" + password + "'";
    
    return jdbcTemplate.queryForObject(query, User.class);
}

// Secure: Parameterized queries prevent injection
public User authenticateUser(String username, String password) {
    String query = "SELECT * FROM users WHERE username=? AND password=?";
    return jdbcTemplate.queryForObject(query, User.class, username, hashPassword(password));
}

Mitigation Strategies:

• Use parameterized queries and prepared statements
• Implement input validation and sanitization
• Apply principle of least privilege for database accounts
• Use stored procedures with proper input validation

A04:2021 – Insecure Design

Risk Level: High

This new category focuses on risks related to design and architectural flaws, representing missing or ineffective control design.

Common Design Flaws:

• Missing security controls
• Inadequate threat modeling
• Insecure architectural patterns
• Business logic vulnerabilities

// Vulnerable: Insecure password reset design
@PostMapping("/reset-password")
public ResponseEntity<String> resetPassword(@RequestParam String email) {
    User user = userService.findByEmail(email);
    if (user != null) {
        emailService.sendPasswordReset(user.getEmail(), generateResetToken());
    }
    return ResponseEntity.ok("Reset email sent if account exists");
}

// Secure: Proper rate limiting and security controls
@PostMapping("/reset-password")
@RateLimited(maxRequests = 3, timeWindow = "1h")
public ResponseEntity<String> resetPassword(@RequestParam String email, HttpServletRequest request) {
    if (!captchaService.verify(request.getParameter("captcha"))) {
        throw new SecurityException("CAPTCHA verification failed");
    }
    
    User user = userService.findByEmail(email);
    if (user != null) {
        emailService.sendPasswordReset(user.getEmail(), generateSecureResetToken());
    }
    return ResponseEntity.ok("Reset email sent if account exists");
}

A05:2021 – Security Misconfiguration

Risk Level: High

Security misconfiguration occurs when security settings are not implemented, maintained, or updated properly.

Common Misconfigurations:

• Default credentials and configurations
• Unnecessary features enabled
• Missing security headers
• Outdated software components

# Vulnerable: Insecure server configuration
# Default configuration with debug enabled
server.error.include-stacktrace=always
server.error.include-message=always
spring.profiles.active=development

# Secure: Production-ready configuration
server.error.include-stacktrace=never
server.error.include-message=never
spring.profiles.active=production
security.headers.frame=DENY
security.headers.content-type=nosniff

 

A06:2021 – Vulnerable and Outdated Components

Risk Level: High

Using components with known vulnerabilities can compromise application security significantly.

Risk Factors:

• Outdated libraries and frameworks
• Unsupported software versions
• Missing security patches
• Unknown component inventory

Mitigation Strategies:

• Maintain component inventory
• Monitor for security advisories
• Implement automated dependency scanning
• Regular security updates and patching

A07:2021 – Identification and Authentication Failures

Risk Level: High

Previously known as “Broken Authentication,” this category covers failures in user identity confirmation and session management.

Common Authentication Flaws:

• Weak password policies
• Session fixation attacks
• Credential stuffing vulnerabilities
• Missing multi-factor authentication

// Vulnerable: Weak session management
@PostMapping("/login")
public ResponseEntity<String> login(@RequestBody LoginRequest request, HttpSession session) {
    User user = authService.authenticate(request.getUsername(), request.getPassword());
    if (user != null) {
        session.setAttribute("user", user);
        return ResponseEntity.ok("Login successful");
    }
    return ResponseEntity.status(401).body("Authentication failed");
}

// Secure: Proper session management with security controls
@PostMapping("/login")
public ResponseEntity<String> login(@RequestBody LoginRequest request, HttpServletRequest httpRequest) {
    User user = authService.authenticate(request.getUsername(), request.getPassword());
    if (user != null) {
        // Regenerate session ID to prevent fixation
        HttpSession session = httpRequest.getSession(false);
        if (session != null) {
            session.invalidate();
        }
        session = httpRequest.getSession(true);
        session.setAttribute("user", user);
        session.setMaxInactiveInterval(1800); // 30 minutes
        
        return ResponseEntity.ok("Login successful");
    }
    return ResponseEntity.status(401).body("Authentication failed");
}

A08:2021 – Software and Data Integrity Failures

Risk Level: High

This new category focuses on code and infrastructure that doesn’t protect against integrity violations.

Common Integrity Failures:

• Unsigned software updates
• Insecure CI/CD pipelines
• Auto-update mechanisms without verification
• Untrusted deserialization

// Vulnerable: Unsafe deserialization
@PostMapping("/api/deserialize")
public Object deserializeData(@RequestBody byte[] serializedData) {
    try {
        ObjectInputStream ois = new ObjectInputStream(new ByteArrayInputStream(serializedData));
        return ois.readObject();
    } catch (Exception e) {
        throw new RuntimeException("Deserialization failed", e);
    }
}

// Secure: Safe deserialization with validation
@PostMapping("/api/deserialize")
public Object deserializeData(@RequestBody String jsonData) {
    try {
        // Use JSON instead of Java serialization
        ObjectMapper mapper = new ObjectMapper();
        // Validate against expected schema
        return mapper.readValue(jsonData, ExpectedDataType.class);
    } catch (Exception e) {
        throw new RuntimeException("Deserialization failed", e);
    }
}

A09:2021 – Security Logging and Monitoring Failures

Risk Level: Medium

Insufficient logging and monitoring capabilities prevent detection of security incidents and breaches.

Common Monitoring Failures:

• Missing audit logs
• Insufficient log retention
• No alerting mechanisms
• Inadequate incident response

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

Risk Level: Medium

SSRF flaws occur when web applications fetch remote resources without validating user-supplied URLs.

// Vulnerable: Unvalidated URL fetching
@GetMapping("/api/fetch")
public String fetchUrl(@RequestParam String url) {
    try {
        RestTemplate restTemplate = new RestTemplate();
        ResponseEntity<String> response = restTemplate.getForEntity(url, String.class);
        return response.getBody();
    } catch (Exception e) {
        return "Error fetching URL: " + e.getMessage();
    }
}

// Secure: URL validation and allowlist
@GetMapping("/api/fetch")
public String fetchUrl(@RequestParam String url) {
    // Validate URL against allowlist
    if (!urlValidator.isAllowed(url)) {
        throw new SecurityException("URL not allowed");
    }
    
    // Additional validation
    if (url.contains("localhost") || url.contains("127.0.0.1") || url.contains("file://")) {
        throw new SecurityException("Local URLs are not permitted");
    }
    
    try {
        RestTemplate restTemplate = new RestTemplate();
        return restTemplate.getForObject(url, String.class);
    } catch (Exception e) {
        throw new RuntimeException("Error fetching URL", e);
    }
}

Implementing OWASP Top 10 Defense Strategies

1. Secure Development Lifecycle (SDLC)

• Threat modeling during design phase
• Security code reviews and static analysis
• Dynamic application security testing (DAST)
• Penetration testing and vulnerability assessments

2. Security Training and Awareness

• Developer security training programs
• Secure coding guidelines and standards
• Regular security updates and briefings
• Security champions program

3. Automated Security Testing

• Static Application Security Testing (SAST)
• Dynamic Application Security Testing (DAST)
• Interactive Application Security Testing (IAST)
• Dependency scanning and management

Conclusion

The OWASP Top 10 provides a critical foundation for web application security programs. Understanding these vulnerabilities is essential for:

Security Professionals

• Vulnerability assessment and penetration testing
• Security architecture and design reviews
• Incident response and forensic analysis

Development Teams

• Secure coding practices and code reviews
• Security testing integration in CI/CD pipelines
• Threat modeling and risk assessment

Key Takeaways

1. Broken Access Control remains the #1 risk in modern applications
2. Injection attacks continue to pose critical threats to data integrity
3. Insecure Design emphasizes the importance of security-by-design principles
4. Security Misconfiguration highlights the need for proper deployment practices

Stay current with OWASP resources and apply these security principles to build more resilient web applications. Regular security assessments using OWASP Top 10 as a framework help organizations identify and mitigate critical vulnerabilities before they can be exploited.

Explore OWASP Resources →

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