Technical Analysis of "Shopify Account Takeover"

Overview

OphionSecurity’s blog post uncovers a critical vulnerability in Shopify that allowed for the takeover of any Shopify user account. The write-up meticulously details the discovery, exploitation, and reporting phases, highlighting the technical aspects behind the vulnerability and how it was effectively mitigated.

Vulnerability Breakdown

1. Focal Point: CSRF on Password Update Endpoint

The core vulnerability was a Cross-Site Request Forgery (CSRF) in the password update functionality of Shopify. CSRF vulnerabilities occur when unauthorized commands are transmitted from a user that the web application trusts.

• Endpoint: The affected endpoint was /admin/users/password/update.
• Issue: The endpoint did not adequately validate the origin of the request, allowing attackers to craft a page that, when visited by an authenticated user, could change their password without their knowledge.

2. Understanding CSRF Vulnerabilities

• CSRF Tokens: Normally, web applications use CSRF tokens to prevent this form of attack. These tokens ensure that the request is genuine and not forged by a malicious actor.
• Any User Context: For this vulnerability to be exploited, the attacker needs the victim to be logged into their Shopify account when they visit a malicious site designed to exploit the vulnerability.

3. The Exploit in Action

• Malicious HTML Form: The attacker creates an HTML form that auto-submits a POST request to the vulnerable /admin/users/password/update endpoint.
• Forged Request: The form contains new credentials (a new password) which, once the user visits the attacker's site, will be submitted to Shopify, effectively updating the victim's password to one controlled by the attacker.
• Payload Example: html <form action="https://shopify.com/admin/users/password/update" method="POST"> <input type="hidden" name="password" value="NewPassword123"> </form> <script>document.forms[0].submit();</script>

4. Steps Taken to Discovery & Report

• Discovery: The vulnerability was identified through detailed examination of Shopify’s handling of form submissions, automated workflows, and manual testing.
• Exploration: Through repeated testing and manipulation, it was confirmed that the password update action lacked proper validation, exposing it to CSRF.
• Reporting: Upon discovery, the OphionSecurity team responsibly reported the issue to Shopify, ensuring the vulnerability details were privately disclosed and a resolution was implemented before public disclosure.

Mitigation Strategies

Shopify’s Response:

• Implement CSRF Tokens: Shopify patched the vulnerability by ensuring that CSRF tokens were properly validated for the password update functionality.
• Strengthening Validation: This involves enhancing backend logic to effectively discern between legitimate and potentially forged requests.

General Best Practices for Developers:

1. CSRF Protection: Always implement and validate CSRF tokens for state-modifying requests.
2. SameSite Cookies: Utilize the SameSite attribute for cookies to restrict cross-origin requests.
3. User Interaction for Sensitive Actions: Require re-authentication or additional verification (e.g., email OTP) before allowing account modifications.
4. Security Headers & Policies: Apply Content Security Policy (CSP) and other security headers to reduce the risk of CSRF and other web-based attacks.

Conclusion

The OphionSecurity team’s discovery of the Shopify account takeover vulnerability underscores the critical importance of robust CSRF protections in web applications, particularly in functionalities dealing with user account management. By ensuring proper CSRF token implementation and adopting best practices, developers can safeguard user data against such potent attack vectors. The write-up serves as an educational resource for security researchers and developers alike, emphasizing responsible disclosure and effective vulnerability management.

For the full details, you can review the original blog post by OphionSecurity here.