Broken Authentication: Understanding and Preventing a Critical Web Security Vulnerability

In October 2013, Adobe suffered a massive data breach that exposed the encrypted passwords and credit card information of millions of users. The breach, which affected approximately 38 million active users, was a result of broken authentication mechanisms. Hackers were able to access Adobe's systems and steal user data, including poorly encrypted passwords. This incident highlights the critical importance of robust authentication systems and the severe consequences of Broken Authentication, a vulnerability that continues to plague many web applications today.

Broken Authentication is a severe security vulnerability that occurs when web applications implement authentication and session management incorrectly. This flaw can lead to unauthorized access, data breaches, and compromised user accounts, as demonstrated by the Adobe incident. In this lesson, we'll explore the concept of Broken Authentication, its impact, and how to prevent such devastating security breaches.

A Specific Technical Example of Broken Authentication

Let's examine a concrete example of broken authentication in a web application. Consider the following scenario involving a flawed password reset mechanism:

Vulnerable Password Reset Functionality

Imagine a web application that allows users to reset their passwords. The process works as follows:

1. User requests a password reset by entering their email address.
2. The application generates a password reset token and sends it to the user's email.
3. The user clicks on the reset link, which includes the token as a parameter.
4. The user is directed to a page where they can enter a new password.

Here's why this login process potentially problematic:

1. Weak Token Generation: If the password reset token is predictable or not sufficiently random, an attacker could potentially guess or generate valid tokens.

2. Token in URL: Sending the token as a URL parameter exposes it to various risks:

   • It may be logged in server logs, browser history, or proxy logs.
   • It can be visible to anyone looking over the user's shoulder.
   • It might be shared unintentionally if the user forwards the link.

3. Lack of Token Expiration: If the token doesn't expire after a short period or after use, an attacker who gains access to the token could use it indefinitely.

4. No User Verification: The reset page doesn't verify that the user requesting the password change is the same user who initiated the reset process.

5. Potential for Enumeration: If the application behaves differently when a valid vs. invalid email is entered, it could allow attackers to enumerate valid user accounts.

6. Insecure Communication: If any part of this process occurs over HTTP instead of HTTPS, the token and new password could be intercepted.

7. No Rate Limiting: Without limits on password reset attempts, an attacker could abuse this feature for denial of service or to brute-force reset tokens.

These vulnerabilities could allow an attacker to take over user accounts by exploiting the password reset functionality, demonstrating a clear case of broken authentication.

Specific Example

Let's supposed this is the URL being sent to reset password:

1https://example.com/reset-password?token=1234567890&user_id=42

This link is vulnerable for several reasons:

1. Predictable token: The token "1234567890" appears to be a simple numeric sequence, which could be easily guessed or brute-forced.
2. User ID exposure: Including the user_id parameter in the URL directly exposes information about the user account structure.
3. Lack of encryption: The token and user ID are sent as plain text in the URL, making them susceptible to interception.
4. No expiration: There's no indication of when this link expires, potentially allowing it to be used indefinitely if intercepted.
5. Sent over HTTP: If this link is sent over HTTP instead of HTTPS, it's vulnerable to man-in-the-middle attacks.

A more secure password reset link might look something like this:

1https://example.com/reset-password?token=a1b2c3d4e5f6g7h8i9j0k1l2m3n4o5p6

This improved version:

• Uses a longer, more random token (harder to guess)
• Doesn't expose the user ID
• Should be sent over HTTPS
• The token should have a short expiration time (e.g., 1 hour)
• Should be single-use only, and not reusable.

Remember, the security of the password reset process doesn't just depend on the link itself, but also on how it's generated, stored, and processed on the server side.

Common Broken Authentication Vulnerabilities

1. Weak password policies Example: A system that allows passwords like "123456" or "password"

2. Credential stuffing Example: An attacker uses a list of email/password combinations from a data breach on Site A to attempt logins on Site B

3. Brute force attacks Example: An attacker uses a script to try thousands of common passwords on a single user account

4. Session fixation Example: An attacker sets a session ID in a user's browser, waits for the user to log in, then uses that same session ID to hijack the authenticated session

   To elaborate:

   1. The attacker creates a malicious link or uses a cross-site scripting (XSS) vulnerability to set a known session ID in the victim's browser.
   2. This session ID is typically set through a cookie or URL parameter.
   3. The victim then logs into the legitimate website, which associates their authenticated session with the attacker-controlled session ID.
   4. Once the victim is logged in, the attacker can use the same session ID to access the victim's account without needing their credentials.
   5. This attack exploits the website's failure to generate new session IDs upon login or to properly validate the origin of session IDs.

5. Insecure session management Example: A website that stores session tokens in easily accessible cookies without encryption or proper expiration

6. Lack of multi-factor authentication Example: A bank website that only requires a username and password for login, without any additional verification step

How to Prevent Broken Authentication

1. Implement strong password policies
2. Use multi-factor authentication
3. Implement proper session management
4. Limit failed login attempts
5. Use secure communication protocols (HTTPS)
6. Implement secure password recovery mechanisms

Tools to Detect Broken Authentication

Several tools can be used to identify and test for broken authentication vulnerabilities:

1. Burp Suite

   • Professional web vulnerability scanner with specific modules for authentication testing
   • Can intercept and modify requests to test various authentication scenarios
   • Example usage:

     # Use Burp Suite's Intruder to perform a brute force attack
     1. Intercept a login request
     2. Send to Intruder
     3. Set payload positions for username and password fields
     4. Load wordlists for common credentials
     5. Start the attack and analyze results
     

2. OWASP ZAP (Zed Attack Proxy)

   • Open-source web application security scanner
   • Includes authentication-specific scan rules
   • Example usage:

     # Use ZAP's Active Scan to test for authentication vulnerabilities
     1. Set up ZAP as a proxy for your browser
     2. Navigate through the target application, including login process
     3. Right-click on a URL in ZAP and select "Attack" -> "Active Scan"
     4. Review the "Alerts" tab for any authentication-related findings
     

3. Hydra

   • Command-line tool for brute-force attacks against various protocols
   • Useful for testing password strength and account lockout policies
   • Example usage:

     1# Perform a brute force attack against a web form
     2hydra -l admin -P /path/to/wordlist.txt example.com http-post-form "/login.php:username=^USER^&password=^PASS^:Login failed"

4. Nmap

   • Network scanning and discovery tool with scripts for authentication testing
   • Example usage:

     1# Use Nmap's http-brute script to test for weak credentials
     2nmap -p80 --script http-brute --script-args 'http-brute.path=/login.php,userdb=users.txt,passdb=passwords.txt' example.com

5. Metasploit

   • Penetration testing framework with modules for testing authentication
   • Example usage:

     1# Use Metasploit's auxiliary/scanner/http/http_login module
     2use auxiliary/scanner/http/http_login
     3set RHOSTS example.com
     4set RPORT 80
     5set USERNAME admin
     6set PASS_FILE /path/to/wordlist.txt
     7set TARGETURI /login.php
     8run

6. Custom Scripts

   • Python or other scripting languages can be used to create tailored tools
   • Example Python script to test for weak session management:

     1import requests
     2
     3def test_session_fixation(url):
     4    # Create a session and get a session ID
     5    session = requests.Session()
     6    response = session.get(url)
     7    initial_session_id = session.cookies.get('session_id')
     8    
     9    # Perform login (replace with actual login process)
     10    login_data = {'username': 'testuser', 'password': 'testpass'}
     11    response = session.post(url + '/login', data=login_data)
     12    
     13    # Check if session ID changed after login
     14    post_login_session_id = session.cookies.get('session_id')
     15    
     16    if initial_session_id == post_login_session_id:
     17        print("Potential session fixation vulnerability detected!")
     18    else:
     19        print("Session ID changed after login. Good practice observed.")
     20
     21# Usage
     22test_session_fixation('https://example.com')

When using these tools, always ensure you have proper authorization to test the target systems and comply with all relevant laws and regulations.