Broken Authentication: Full Methodology for Identifying and Exploiting Vulnerabilities

Broken Authentication is one of the top vulnerabilities affecting web applications today. It is a significant attack vector that can lead to account takeover, unauthorized data access, and more. In this post, we’ll dive into the full methodology for identifying and exploiting broken authentication vulnerabilities, covering everything from reconnaissance to post-exploitation techniques.

Broken Authentication occurs when an application’s authentication system fails to properly enforce security measures like identity verification, session management, and access control. Attackers can exploit these flaws to impersonate legitimate users, often resulting in privilege escalation, access to sensitive data, or even full account takeover.

The OWASP Top Ten lists Broken Authentication as a critical vulnerability. Attackers can exploit issues like improper password storage, session fixation, weak passwords, and more. The consequences of an attack can be severe, making it crucial for security researchers and penetration testers to understand how to identify and exploit these flaws.

Before launching any attack, reconnaissance is essential. The goal here is to gather information about how the web application handles authentication. You’ll need to identify authentication endpoints and gather details such as:

Login and registration pagesPassword reset mechanismsTwo-factor authentication (2FA) implementationsSession cookies and headersBurp Suite: Use Burp Suite’s crawler and spider tools to discover authentication endpoints and analyze how they function.OWASP ZAP: Another great tool for spidering and identifying hidden endpoints.Wfuzz: This is perfect for fuzzing login forms and identifying weak authentication mechanisms.

Use these tools to identify pages like login forms (/login, /signin, /auth, etc.), password reset endpoints (/reset-password), and account management interfaces. Understanding the way these pages interact with the backend can give valuable clues on how the authentication process works.

Once you’ve identified authentication endpoints, the next step is to assess how they handle authentication mechanisms, such as passwords, session tokens, and multi-factor authentication.

Check for weak password policies that can be easily guessed or cracked. Common issues include:

No minimum password lengthNo character complexity requirements (e.g., lowercase, uppercase, digits)No account lockout after multiple failed login attempts

Use brute-force tools such as Hydra or Burp Intruder to test for weak or common passwords. A tool like SecLists provides a huge collection of default usernames and passwords, which can be used for password spraying attacks.

Session management flaws are another critical aspect of broken authentication. Test how the application handles session cookies, including:

Session fixation: Can you set your own session ID before login and still authenticate as another user?Session timeout: Does the session automatically expire after a reasonable amount of inactivity?Cookie security: Check if cookies are set with the HttpOnly and Secure flags to prevent interception.

Using tools like Burp Suite or Cookie Editor (a browser extension), you can manually manipulate session cookies and observe any unexpected behaviors. Exploiting weak session management can often lead to unauthorized access to users’ accounts.

Once you’ve identified potential vulnerabilities in the authentication mechanisms, it’s time to exploit them. Here’s how you can proceed with common attack vectors:

Brute forcing login pages with weak credentials is a straightforward attack, especially when password policies are lax. This can be done using tools like Hydra or Burp Intruder.

Brute force your target application with various common usernames (e.g., admin, root, user, etc.) and passwords (e.g., 123456, password, qwerty). Monitor for successful login attempts or account lockout responses.

Password spraying involves trying a few common passwords across many user accounts, which reduces the chances of triggering account lockouts. Passwords like Password123 or Welcome2024 are often used in these attacks. Tools like Hydra can be used to automate password spraying.

Session fixation occurs when an attacker can set or predict a session ID before the victim logs in. This allows the attacker to hijack the victim’s session after login. Test for session fixation by manually setting a session ID cookie before logging in as a legitimate user. If the session remains the same, it is vulnerable.

If you have access to a list of valid username and password pairs (from data breaches or previous attacks), you can use credential stuffing techniques to attempt login using these credentials. This attack is very effective when users reuse passwords across multiple sites.

Tools for Credential Stuffing:

Sentry MBASniprBurp Suite Intruder

Once you’ve successfully exploited broken authentication, it’s important to consider what you can do with the access you’ve gained. This is where privilege escalation and persistence come into play.

Escalate Privileges: After compromising a low-privileged account, check for ways to escalate to admin-level access. Look for flaws in the authorization logic or in the user role management.Establish Persistence: If you’ve gained administrative access, look for ways to maintain access, such as creating a new user account with elevated privileges or adding persistent session tokens.

As a penetration tester or security professional, your job is not just to exploit vulnerabilities but also to advise on how to fix them. Here are some best practices to prevent broken authentication:

Enforce strong password policies: Require a combination of upper/lowercase letters, numbers, and special characters. Implement a password length requirement (e.g., 12 characters or more).Implement multi-factor authentication (MFA): Enforce MFA for all users, particularly for critical actions or high-privileged accounts.Session security: Ensure that sessions are invalidated after logout and that session cookies are set to HttpOnly and Secure.Limit login attempts: Implement account lockout or CAPTCHA mechanisms to mitigate brute-force and password spraying attacks.Use OAuth, OpenID Connect, or other secure token-based authentication protocols: These protocols allow for secure token management, reducing the chances of session-related vulnerabilities.

Authentication endpoints are often vulnerable if they are misconfigured or improperly secured. Start by mapping out the application’s attack surface. Look for pages like:

Login pages (e.g., /login, /signin, /authenticate, /auth)Registration forms (e.g., /register, /signup, /new-user)Password reset and recovery forms (e.g., /reset-password, /forgot-password, /change-password)Account management and logout functions (e.g., /profile, /logout)

Automated Crawling and Fuzzing: Tools like Burp Suite and OWASP ZAP allow you to automate the discovery of these endpoints. Set them to crawl the application, and filter out unnecessary traffic to focus specifically on authentication-related endpoints.

Once you have identified visible authentication pages, there may still be hidden or poorly protected endpoints that can be exploited. Using tools like dirb or gobuster, perform a directory brute-force attack on the domain to uncover potential hidden authentication-related paths.

For example:👇👇👇

dirb http://target.com /path/to/wordlist.txt

Look for unusual or weak endpoints that could be used for authentication, such as forgotten admin paths, auxiliary authentication points, or misconfigured password reset functionality.

One critical area to assess is how passwords are stored. Passwords should never be stored in plaintext. Common insecure storage methods include:

Plaintext storage: Passwords saved as-is in the database.Weak hashing algorithms: Algorithms like MD5 or SHA1 are outdated and vulnerable to modern cracking techniques.

How to Test: Check whether the application uses modern cryptographic hashing algorithms like bcrypt, PBKDF2, or Argon2. Tools like Hashcat or John the Ripper can help in testing the strength of hashed passwords, assuming you have access to the database or an exposed hash.

It’s essential to test for rate-limiting issues that might allow brute force attacks. Common flaws include:

No lockout mechanism after multiple failed login attempts.Excessive timeouts after many unsuccessful logins.Lack of CAPTCHA or alternative measures to mitigate automated login attempts.

Tools like Hydra or Burp Suite Intruder are perfect for automated brute-force testing. When running these tools, watch for subtle errors in the application’s response that could indicate login failures, such as specific HTTP status codes (403 Forbidden or 401 Unauthorized).

Here’s an example of using Hydra for a brute force attack:

hydra -l admin -P /path/to/passwordlist.txt http://target.com/login

If the application implements 2FA or MFA, it’s essential to verify its configuration. Look for weak or improperly implemented 2FA methods, such as:

SMS-based authentication: Prone to SIM swapping and interception attacks.Email-based codes: If the attacker gains access to the user’s email, they can bypass the 2FA mechanism.Fallback authentication methods: Check if there are insecure recovery mechanisms in place that can bypass MFA.

Automated tools can help test the robustness of 2FA implementations. However, a manual review is also recommended, especially to check how fallback or recovery mechanisms work.

Once you’ve found vulnerabilities in the authentication mechanisms, it’s time to leverage them. Here are some advanced techniques for exploiting broken authentication.

In a session fixation attack, an attacker forces a victim to use a predefined session ID. This is possible when the application fails to properly regenerate session IDs after login, allowing attackers to impersonate the victim once they log in.

To test for session fixation:

Set your own session ID before the victim logs in.Attempt to use that session ID after the victim authenticates.

If the session persists and provides access to the victim’s account, the application is vulnerable to session fixation.

Web applications should automatically expire sessions after a period of inactivity. Some applications, however, leave sessions open indefinitely, allowing attackers to hijack stale sessions. If the application doesn’t expire sessions correctly, the attacker can reuse the session to impersonate the user after they’ve logged out or after a prolonged period.

How to Test:

Log in to the application.Wait for the session to expire (or manipulate session expiry through browser tools).Use the same session token after a prolonged period to see if access is granted.

If the session is still valid after a long period, the application may have insufficient session expiration.

In applications that use OAuth or JWT (JSON Web Tokens) for authentication, it’s crucial to ensure that these tokens are securely implemented. Common issues include:

Weak or predictable signing keys: Tokens that can be tampered with or forged.Token reuse: Tokens that don’t expire or are reused across different sessions.

If you have access to the token, you can test whether it can be replayed or manipulated to gain unauthorized access. JWT tokens can be decoded using online tools or libraries like jwt.io, allowing you to inspect or modify the payload.

Once you’ve exploited broken authentication, the next step is post-exploitation. This involves maintaining access to the compromised system and looking for opportunities to escalate privileges.

Creating Backdoors: Once logged in as a user, check for account management functionality. You may be able to create a new admin account or modify roles to elevate your privileges.Session Hijacking: In cases where session tokens or cookies are used for authentication, hijack an active session or inject your own token into your session to retain access.Stored Credentials: Look for any stored credentials or API keys within the application (such as in local storage, cookies, or configuration files) that can help you escalate privileges.

After accessing a low-privileged user account, the next step is to escalate your privileges:

Role Misconfigurations: Check for any role-based access control (RBAC) misconfigurations, such as low-privileged users being able to access administrative functions.Insecure Direct Object References (IDOR): Manipulate parameters or URLs to gain access to unauthorized resources, such as another user’s data or administrative pages.

Now that you understand how to exploit broken authentication, here’s how organizations can defend against these attacks:

Implement Strong Authentication: Enforce complex passwords and MFA. Passwords should never be stored in plaintext, and session tokens should always be secure (use HttpOnly, Secure, and SameSite cookie flags).Session Management Best Practices: Regenerate session IDs on login and logout, and ensure sessions expire after a reasonable inactivity period. Implement rate-limiting and CAPTCHA to defend against brute force and credential stuffing attacks.Monitoring and Logging: Implement continuous monitoring of login attempts, unusual access patterns, and failed login attempts. Use security information and event management (SIEM) tools to detect suspicious behavior