Authentication Bypass Basic

4 min readJul 11, 2024

Introduction

Authentication bypass is a security vulnerability that allows an attacker to access resources that require authentication without actually authenticating. This vulnerability allows the attacker to gain access to portions of the application or data the target is trying to protect. Depending on the exposed portions, this can be a very critical issue in a web application.

What is Authentication Bypass?

Authentication bypass occurs when an application fails to properly verify user credentials, allowing an attacker to access resources meant for authenticated users. This can happen due to insufficient or missing authentication mechanisms within the application.

Methods of Authentication Bypass

Authentication bypass can be achieved through two main methods: manual access and automated script usage.

Manual Access:

Manual access involves examining the application’s site map and directly accessing the pages listed, rather than following the usual navigation flow. This method includes:

Accessing pages using a browser
Inspecting and manipulating URL parameters
Using keys and IDs to gain access

Automated Script Usage:

Automated scripts make exploiting this flaw easier. Scripts can brute force directory and file names to find valid filenames that allow access. This method involves:

Writing scripts to brute force IDs and keys
Guessing page names through brute force to find accessible pages

Detecting Authentication Bypass Vulnerability

When a security tester finds an authentication bypass issue, they need to determine what the vulnerability provides access to. Does it grant access to the entire site or just a portion of it? Understanding this is crucial to assess the severity of the vulnerability.

Conclusion

Authentication bypass is a serious security flaw that allows attackers to access unauthorized areas within an application. Both manual and automated methods can be used to exploit these vulnerabilities, significantly compromising the security of the application. Identifying and addressing such flaws is critical to maintaining application security.

Flask Application Demonstrating Authentication Bypass Vulnerability

In this section, we will create a simple Flask application with an authentication bypass vulnerability. This application is for educational purposes only and is not recommended for use in production environments.

Install Required Libraries

To install Flask, use the following command:

pip install flask

Create the Flask Application

Copy the following code into a file named app.py. This code demonstrates a simple Flask application with an authentication bypass vulnerability.

from flask import Flask, request, redirect, url_for, session, render_template

app = Flask(__name__)
app.secret_key = 'supersecretkey'users = {
    'admin': 'password123',
    'user': 'userpass'
}@app.route('/')
def home():
    if 'username' in session:
        return render_template('home.html', username=session['username'])
    return render_template('home.html', username=None)@app.route('/login', methods=['GET', 'POST'])
def login():
    if request.method == 'POST':
        username = request.form['username']
        password = request.form['password']
        if username in users and users[username] == password:
            session['username'] = username
            return redirect(url_for('home'))
        return render_template('login.html', error=True)
    return render_template('login.html', error=False)@app.route('/logout')
def logout():
    session.pop('username', None)
    return redirect(url_for('home'))@app.route('/admin')
def admin():
    return render_template('admin.html')if __name__ == '__main__':
    app.run(debug=True)

HTML Templates

Create a directory named templates and inside it, create the following files:

base.html

<!DOCTYPE html>
<html lang="en">
<head>
    <meta charset="UTF-8">
    <meta name="viewport" content="width=device-width, initial-scale=1, shrink-to-fit=no">
    <title>{% block title %}Flask App{% endblock %}</title>
    <link rel="stylesheet" href="https://stackpath.bootstrapcdn.com/bootstrap/4.5.2/css/bootstrap.min.css">
</head>
<body>
    <nav class="navbar navbar-expand-lg navbar-light bg-light">
        <a class="navbar-brand" href="{{ url_for('home') }}">FlaskApp</a>
        <div class="collapse navbar-collapse" id="navbarNav">
            <ul class="navbar-nav ml-auto">
                {% if username %}
                    <li class="nav-item">
                        <a class="nav-link" href="#">{{ username }}</a>
                    </li>
                    <li class="nav-item">
                        <a class="nav-link" href="{{ url_for('logout') }}">Logout</a>
                    </li>
                {% else %}
                    <li class="nav-item">
                        <a class="nav-link" href="{{ url_for('login') }}">Login</a>
                    </li>
                {% endif %}
            </ul>
        </div>
    </nav>
    <div class="container mt-4">
        {% block content %}{% endblock %}
    </div>
    <script src="https://code.jquery.com/jquery-3.5.1.slim.min.js"></script>
    <script src="https://cdn.jsdelivr.net/npm/@popperjs/core@2.5.2/dist/umd/popper.min.js"></script>
    <script src="https://stackpath.bootstrapcdn.com/bootstrap/4.5.2/js/bootstrap.min.js"></script>
</body>
</html>

home.html

{% extends "base.html" %}
{% block title %}Home{% endblock %}
{% block content %}
<div class="jumbotron">
    <h1 class="display-4">Welcome{% if username %}, {{ username }}{% endif %}!</h1>
    {% if username %}
        <p class="lead">You are logged in. <a href="{{ url_for('logout') }}" class="btn btn-primary btn-lg">Logout</a></p>
    {% else %}
        <p class="lead">You are not logged in. <a href="{{ url_for('login') }}" class="btn btn-primary btn-lg">Login</a></p>
    {% endif %}
</div>
{% endblock %}

login.html

{% extends "base.html" %}
{% block title %}Login{% endblock %}
{% block content %}
<h2>Login</h2>
{% if error %}
    <div class="alert alert-danger" role="alert">
        Invalid credentials. Please try again.
    </div>
{% endif %}
<form method="post">
    <div class="form-group">
        <label for="username">Username</label>
        <input type="text" class="form-control" id="username" name="username" required>
    </div>
    <div class="form-group">
        <label for="password">Password</label>
        <input type="password" class="form-control" id="password" name="password" required>
    </div>
    <button type="submit" class="btn btn-primary">Login</button>
</form>
{% endblock %}

admin.html

{% extends "base.html" %}
{% block title %}Admin{% endblock %}
{% block content %}
<h2>Admin Page</h2>
<p>Welcome to the admin page. <a href="{{ url_for('home') }}" class="btn btn-secondary">Home</a></p>
{% endblock %}h

Run the Application

Run the following command in your terminal to start the appa

python app.py

Test the Application

Open your browser and navigate to http://127.0.0.1:5000 to test your modernized application. Try accessing the /admin page directly by entering http://127.0.0.1:5000/admin in the browser. You will notice that you can access this page without logging in.