Day 30of 30 Day — 30 Vulnerabilities | Cross-Site Request Forgery (CSRF)

Day 30: Mastering Account Takeover through CSRF Token Reuse — Essential Tricks & Techniques Based on Personal Experience and Valuable POCs

In collaboration with Sunil Kumawat (LinkedIn | Twitter)

Hey security enthusiasts, Abhijeet (Twitter) here, back with another deep dive into web security. Today, we’re focusing on a subtle yet dangerous attack vector — Account Takeover through CSRF Token Reuse. This vulnerability can have serious implications if exploited, allowing attackers to hijack user accounts and gain unauthorized access. Let’s break down the essentials.

What is Account Takeover through CSRF Token Reuse?

Account Takeover through CSRF Token Reuse occurs when an attacker exploits the reuse of Cross-Site Request Forgery (CSRF) tokens to perform unauthorized actions on behalf of a legitimate user. CSRF tokens are intended to protect against unauthorized requests, but if they are reused or not properly implemented, attackers can trick users into executing actions that compromise their accounts.

How Does It Work?

The attack typically involves tricking a victim into performing an action, such as clicking a malicious link or submitting a form, which sends a request with a reused or predictable CSRF token. If the application does not validate the token properly or allows its reuse, the attacker can perform actions on behalf of the victim, leading to account takeover or other security breaches.

Form Submissions:

Review how your application handles form submissions, particularly those involving sensitive actions like changing passwords, updating user profiles, or making transactions.

CSRF Token Implementation:

Inspect the implementation of CSRF tokens across your application. Ensure tokens are unique per request and user session, and are validated correctly on the server side.

Session Handling Mechanisms:

Analyze how your application manages user sessions in relation to CSRF tokens. Weak session management can contribute to token reuse vulnerabilities.

Manual Testing:

Attempt to reuse a CSRF token across multiple requests or sessions. If the application accepts the reused token without proper validation, it indicates a vulnerability.Test form submissions by intercepting requests and modifying CSRF tokens to see if the application accepts the altered token.

Automated Tools:

Use tools like Burp Suite’s CSRF vulnerability scanner or OWASP ZAP to identify weaknesses in the application’s CSRF protection mechanisms. These tools can automate the detection of predictable or reusable CSRF tokens.

Session Monitoring:

Monitor session behavior during sensitive actions to identify if CSRF tokens are being reused or improperly validated across different requests or sessions.

Basic Payloads:

Token Reuse in Form Submission: Submit a form with a CSRF token, capture the request, and reuse the same token in a subsequent request to see if the application accepts it.Predictable Token Attack: Analyze the pattern of generated CSRF tokens. If they are predictable, attempt to craft a valid token and use it to perform unauthorized actions.

Advanced Payloads:

Session Hijacking with CSRF Token Reuse: Combine CSRF token reuse with session hijacking techniques. If an attacker can predict or steal a CSRF token, they can hijack a user session and take over the account.Cross-Domain Exploitation: Use cross-site scripting (XSS) to inject a malicious script that captures and reuses a CSRF token across different domains, leading to a full account takeover.

Token Predictability:

Exploit weak or predictable CSRF tokens by analyzing patterns in token generation. If the token is based on easily guessable data (e.g., timestamps), attackers can craft valid tokens without user interaction.

Token Reuse in Multi-Step Forms:

In applications using multi-step forms, attempt to reuse the CSRF token from an earlier step in subsequent steps. If the token is not revalidated at each step, it can be reused to bypass security checks.

Cross-Site Scripting (XSS) Leveraging:

Use XSS vulnerabilities to inject malicious scripts that automatically reuse CSRF tokens. This technique can silently perform actions on behalf of the victim without their knowledge.

POC 1: Token Reuse in Password Reset

A. Description:

Exploit a vulnerability where a CSRF token is reused during a password reset process.

B. Steps to Reproduce:

Initiate a password reset request and capture the CSRF token.Attempt to reuse the same token in a subsequent password reset request.If the application accepts the reused token, reset the password and take over the account.

C. Impact:

Successful exploitation allows the attacker to reset the victim’s password, effectively taking over their account.

POC 2: Predictable Token Generation

A. Description:

Exploit predictable CSRF tokens to perform unauthorized actions.

B. Steps to Reproduce:

Analyze the pattern of CSRF tokens generated by the application.Craft a valid token based on the observed pattern.Use the crafted token to submit a form or perform an action on behalf of another user.

C. Impact:

The attacker can perform sensitive actions like changing account settings or making transactions without the victim’s consent.

POC 3: XSS-Driven CSRF Token Reuse

A. Description:

Leverage an XSS vulnerability to capture and reuse a CSRF token.

B. Steps to Reproduce:

Identify an XSS vulnerability in the target application.Inject a script that captures the CSRF token from the victim’s session.Use the captured token to perform actions on behalf of the victim, leading to account takeover.

C. Impact:

The attacker can take over the victim’s account by silently submitting forms or making changes on their behalf.

Mitigation Strategies:

Unique Per-Request Tokens: Ensure CSRF tokens are unique for each request and are properly validated on the server side.Session-Tied Tokens: Tie CSRF tokens to specific user sessions, making them invalid if reused across different sessions.Token Expiry: Implement token expiration mechanisms to invalidate old tokens, reducing the risk of reuse.Regular Security Audits: Conduct regular security audits and penetration testing to identify and fix CSRF-related vulnerabilities.

Final Thoughts: Account Takeover through CSRF Token Reuse is a critical vulnerability that can lead to significant security breaches if not properly addressed. By understanding how these attacks work and implementing robust CSRF protection strategies, you can safeguard your applications from potential exploitation (OWASP, PortSwigger).

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This wraps up our 30-day series, but stay tuned for more advanced topics and deep dives into web security!