Understanding OWASP Top 10 for Beginners

If you're starting your journey into Web Application Penetration Testing (WAPT) or Bug Bounty Hunting, one of the first things you'll hear about is the OWASP Top 10. This list contains the most critical security risks found in modern web applications.

In this article, we'll explore each OWASP Top 10 vulnerability in simple language with practical examples.

What is OWASP?

OWASP (Open Worldwide Application Security Project) is a non-profit organization that helps improve software security.

One of its most famous publications is the OWASP Top 10, which lists the most common and dangerous web application vulnerabilities.

These vulnerabilities are frequently encountered during:

• Web Application Penetration Testing (WAPT)
• Vulnerability Assessment and Penetration Testing (VAPT)
• Bug Bounty Programs
• Security Audits

1. Broken Access Control

Broken Access Control occurs when an application fails to properly enforce restrictions on what authenticated or unauthenticated users are allowed to access. As a result, attackers may view, modify, or delete resources and perform actions beyond their intended permissions.

Simply put:

The application fails to properly check what a user is allowed to do.

Practical Example

Imagine a banking website.

User A accesses:

https://bank.com/profile?id=100

https://bank.com/profile?id=100

The attacker changes it to:

https://bank.com/profile?id=101

https://bank.com/profile?id=101

If User A can now see User B's profile, the application suffers from Broken Access Control.

Common Types

• Vertical Privilege Escalation
• Horizontal Privilege Escalation
• Insecure Direct Object Reference (IDOR)
• Force Browsing
• Parameter Tampering

Impact

• Unauthorized Access
• Data Leakage
• Account Takeover
• Privilege Escalation

2. Security Misconfiguration

Security Misconfiguration occurs when an application, server, or cloud service is configured insecurely, exposing unnecessary functionality or sensitive information to attackers.

Simply put:

The application or server is not securely configured.

Practical Example

A website accidentally enables directory listing.

Visiting:

https://example.com/uploads/

https://example.com/uploads/

shows:

backup.zip
users.xlsx
config.txt

backup.zip
users.xlsx
config.txt

Anyone can browse and download sensitive files.

Common Types

• Default Passwords
• Debug Mode Enabled
• Directory Listing
• Missing Security Headers
• Exposed Admin Panels

Impact

• Information Disclosure
• Server Compromise
• Unauthorized Access
• Increased Attack Surface

3. Software Supply Chain Failures

Software Supply Chain Failures occur when applications trust third-party software, libraries, packages, or dependencies that have been compromised or maliciously modified.

Simply put:

The application blindly trusts third-party software or dependencies.

Practical Example

A developer installs a public package named:

company-utils

company-utils

An attacker has uploaded a malicious package with the same name.

The build server downloads the attacker's package, compromising the application.

Common Types

• Dependency Confusion
• Typosquatting
• Supply Chain Attacks
• Malicious Third-Party Libraries
• Compromised Software Updates

Impact

• Malware Installation
• Remote Code Execution
• Data Breaches
• Complete Application Compromise

4. Cryptographic Failures

Cryptographic Failures occur when sensitive information is not properly protected using encryption or secure cryptographic techniques.

Simply put:

The application fails to properly protect sensitive data.

Practical Example

A website sends login credentials over:

http://example.com/login

http://example.com/login

instead of:

https://example.com/login

https://example.com/login

An attacker on the same network can intercept the credentials.

Common Types

• HTTP instead of HTTPS
• Plaintext Password Storage
• Weak Hashing Algorithms (MD5, SHA1)
• Hardcoded API Keys
• Unencrypted Sensitive Data

Impact

• Password Disclosure
• Identity Theft
• Financial Fraud
• Data Breaches

5. Injection

Injection occurs when untrusted user input is interpreted as commands or queries by an interpreter.

Simply put:

The application executes user input without proper validation.

Practical Example

Application Query:

SELECT * FROM users
WHERE username='$user';

SELECT * FROM users
WHERE username='$user';

Attacker enters:

' OR '1'='1

' OR '1'='1

The query returns all user records.

Common Types

• SQL Injection
• Command Injection
• LDAP Injection
• XPath Injection
• NoSQL Injection

Impact

• Authentication Bypass
• Database Dump
• Remote Code Execution
• Full Server Compromise

6. Insecure Design

Insecure Design occurs when security is not properly considered during the application's design phase.

Simply put:

The application's design itself is insecure.

Practical Example

A login page allows unlimited password attempts.

admin
password1

admin
password2

admin
password3

admin
password1

admin
password2

admin
password3

There is no account lockout, CAPTCHA, or rate limiting.

Common Types

• Missing Rate Limiting
• Weak OTP Design
• Business Logic Flaws
• Unlimited Coupon Reuse
• Weak Password Reset Flow

Impact

• Brute Force Attacks
• Account Takeover
• Business Logic Abuse
• Financial Loss

7. Authentication Failures

Authentication Failures occur when weaknesses in the authentication process allow attackers to compromise user accounts.

Simply put:

The application fails to properly verify a user's identity.

Practical Example

The application allows unlimited login attempts.

An attacker tries:

admin : 123456
admin : password
admin : admin123

admin : 123456
admin : password
admin : admin123

until they successfully log in.

Common Types

• Weak Passwords
• Brute Force Attacks
• Credential Stuffing
• Missing Multi-Factor Authentication (MFA)
• Session Hijacking
• Username Enumeration

Impact

• Account Takeover
• Unauthorized Access
• Identity Theft
• Privilege Escalation

8. Software and Data Integrity Failures

Software and Data Integrity Failures occur when applications trust software updates, plugins, libraries, or data without verifying their integrity.

Simply put:

The application trusts software or data without verification.

Practical Example

A developer installs a compromised third-party package that contains hidden malicious code.

The application becomes infected after deployment.

Common Types

• Unverified Software Updates
• Malicious CI/CD Pipelines
• Compromised Plugins
• Unsafe Deserialization
• Insecure Auto-Updates

Impact

• Malware Installation
• Remote Code Execution
• Data Breaches
• Full Application Compromise

9. Security Logging and Alerting Failures

Security Logging and Alerting Failures occur when an application fails to properly record or notify administrators about suspicious activities.

Simply put:

The application does not detect or alert on attacks.

Practical Example

An attacker performs hundreds of failed login attempts.

The application:

• Does not log the activity.
• Does not alert administrators.
• Does not lock the account.

The attack continues unnoticed.

Common Types

• Missing Audit Logs
• Missing Security Alerts
• Poor Monitoring
• No Failed Login Tracking
• Weak Incident Response

Impact

• Delayed Attack Detection
• Undetected Data Breaches
• Extended Attacker Access
• Difficult Forensic Investigation

10. Mishandling of Exceptional Conditions

Mishandling of Exceptional Conditions occurs when an application improperly handles errors, unexpected inputs, or abnormal situations.

Simply put:

The application does not safely handle unexpected conditions or errors.

Practical Example

A user uploads a file larger than the allowed limit.

Instead of displaying a friendly error message, the server crashes and reveals:

java.lang.NullPointerException
at com.example.upload.FileHandler.java:125

java.lang.NullPointerException
at com.example.upload.FileHandler.java:125

This exposes internal application details to an attacker.

Common Types

• Unhandled Exceptions
• Stack Trace Disclosure
• Application Crashes
• Resource Exhaustion
• Improper Error Handling

Impact

• Information Disclosure
• Denial of Service (DoS)
• Application Crashes
• Easier Vulnerability Discovery