OWASP Top 10: 2025 — A Simple Guide for Beginners

OWASP (Open Worldwide Application Security Project) publishes the Top 10 to highlight some of the most important security risks found in web applications.

For someone starting in web penetration testing, the list can initially feel like a collection of complicated security terms. But the underlying ideas are actually quite straightforward.

In this article, I'll break down the OWASP Top 10: 2025 in simple, practical terms.

1. A01:2025 — Broken Access Control

In simple words: A user can access something that they shouldn't be allowed to access.

Imagine you're logged in as User A and your profile URL looks like:

/profile/123

You change the number to:

/profile/124

and suddenly you can view another user's information.

That's a potential Broken Access Control issue.

The application should check whether the logged-in user is actually authorized to access that resource.

What does a pentester look for?

A penetration tester may ask:

"Can I access another user's data by changing an ID?"

Or:

"Can a normal user access an administrator function?"

The important distinction is:

Authentication: Who are you? Authorization: What are you allowed to access?

2. A02:2025 — Security Misconfiguration

In simple words: The application, server, or security settings have been configured incorrectly.

Even a well-written application can become vulnerable because of poor configuration.

For example:

• Default passwords are still being used.
• Debug mode is enabled in production.
• Directory listing is enabled.
• Unnecessary services are exposed.
• Detailed error messages reveal internal information.
• Unnecessary features or services are enabled.

Imagine visiting a website and receiving an error message that reveals internal server paths, database information, or configuration details.

The underlying software might not necessarily be vulnerable — but the configuration is exposing information that shouldn't be exposed.

The simple idea:

Security Misconfiguration = something was configured in an insecure way.

3. A03:2025 — Software Supply Chain Failures

Modern applications rarely consist entirely of code written by the development team.

Developers rely on:

• Open-source libraries
• Frameworks
• Packages
• APIs
• Third-party services
• Development tools

This creates a software supply chain.

If one of those components is vulnerable or compromised, the application using it may also become exposed.

For example, imagine your application depends on a third-party library. A vulnerability is discovered in that library, but your application is still using an outdated version.

Your own code may look perfectly fine, but the dependency introduces a security risk.

The simple idea:

Don't only secure your own code. Know what your application depends on.

This is why dependency management and software composition analysis are important parts of modern application security.

4. A04:2025 — Cryptographic Failures

In simple words: Sensitive information isn't properly protected.

Applications regularly handle sensitive information such as:

• Passwords
• Personal information
• Financial information
• Authentication tokens
• Confidential business data

If this information isn't properly protected, an attacker who gains access to it may be able to read or misuse it.

Examples include:

• Storing passwords insecurely
• Using weak cryptographic algorithms
• Poor key management
• Sending sensitive information without proper transport protection
• Accidentally exposing encryption keys

For example, storing passwords as plain text is a serious security mistake.

Instead of:

ahad123

a properly designed application should use an appropriate password-hashing mechanism so that the original password isn't directly stored.

The simple idea:

Sensitive data needs strong protection — both when stored and when transmitted.

5. A05:2025 — Injection

Injection occurs when an application takes user-controlled input and unintentionally treats it as part of a command or query.

This is one of the classic areas of web application security.

For example, an application may take user input and use it to construct a database query.

If the application doesn't properly separate data from commands, an attacker may be able to manipulate the query.

SQL Injection is a well-known example, but injection isn't limited to SQL.

It can also involve things such as:

• Command Injection
• LDAP Injection
• Other interpreter-based attacks

The basic problem is:

User Input
    ↓
Application
    ↓
Interpreter / Database / Command

User Input
    ↓
Application
    ↓
Interpreter / Database / Command

If the application incorrectly trusts the input, the attacker may influence what gets executed.

The simple idea:

Can my input be interpreted as something more than just data?

6. A06:2025 — Insecure Design

This one is slightly different from a configuration problem.

Insecure Design means the security weakness exists because of how the application was designed.

Imagine an online banking application that allows unlimited money transfers without considering transaction limits, unusual activity, or additional verification.

Even if the server is configured perfectly, the application may still have a security problem because the business logic itself wasn't designed securely.

This is why security should be considered during the design phase rather than being added at the very end of development.

The simple idea:

If security wasn't considered during the design, fixing the configuration later may not solve the underlying problem.

7. A07:2025 — Authentication Failures

Authentication is the process of verifying who you are.

Authentication failures occur when an application doesn't properly protect its login or session mechanisms.

Examples can include:

• Weak password policies
• Brute-force attacks
• Poor session management
• Vulnerable password-reset functionality
• Authentication bypasses
• Problems with multi-factor authentication
• Sessions that aren't properly invalidated

For example, if a login system allows an attacker to make thousands of password attempts without meaningful protection, it may be vulnerable to brute-force attacks.

The simple idea:

Can I bypass, abuse, or weaken the process that proves who I am?

8. A08:2025 — Software or Data Integrity Failures

Applications often trust software, updates, files, or data that come from somewhere else.

The problem occurs when the application doesn't properly verify the integrity or authenticity of that trusted software or data.

Imagine an application downloads an update but doesn't verify whether the update was actually produced by the trusted developer.

If an attacker manages to modify the update, the application could unknowingly install malicious code.

The same general principle applies to data:

Can something the application trusts be modified without being detected?

This is why mechanisms such as integrity verification, secure update processes, and trusted sources are important.

9. A09:2025 — Security Logging and Alerting Failures

Imagine an attacker is repeatedly attempting to log in to an administrator account.

They try:

10 attempts
100 attempts
1,000 attempts

10 attempts
100 attempts
1,000 attempts

But the application doesn't properly log the activity and nobody receives an alert.

The attack could continue without anyone noticing.

This is where security logging and alerting become important.

Applications should generate useful security-related logs and organizations should have appropriate monitoring and alerting mechanisms.

For a security team, logs can provide valuable information about:

• Failed login attempts
• Suspicious requests
• Privilege changes
• Unexpected activity
• Potential attacks

The simple idea:

If an attack happens but nobody notices it, the security controls have a serious visibility problem.

This area is particularly relevant when learning about SOC, SIEM, detection engineering, and incident response.

10. A10:2025 — Mishandling of Exceptional Conditions

Applications don't always operate under perfect conditions.

Users enter unexpected input. Servers fail. Databases become unavailable. Requests time out. Resources run out.

The important question is:

What does the application do when something goes wrong?

Poor error handling can sometimes expose sensitive information or cause the application to enter an unsafe state.

For example, imagine a payment operation that partially completes and then encounters an error.

If the application doesn't properly handle that situation, the system could end up in an inconsistent state.

Errors can also expose internal information such as:

• File paths
• Stack traces
• Database details
• Internal configuration

The simple idea:

A secure application should also behave securely when things go wrong.

Simple Mental Model

If you're beginning your journey into web security, remember these five words:

Access → Configuration → Input → Identity → Visibility

Then gradually expand that understanding into all ten OWASP categories.

The goal isn't simply to know what A01, A02, or A05 means.

The goal is to look at a web application and start asking:

"Where does the application trust the user when it shouldn't?"

That's where your penetration-testing mindset begins.