Bypass SSL Pinning

TL;DR

SSL certificate pinning protects against man-in-the-middle attacks by validating a specific server’s certificate instead of trusting any certificate signed by a trusted Certificate Authority. This guide explains how to bypass SSL pinning using common vulnerabilities and tools, primarily focusing on techniques like weak implementations or exploiting outdated libraries.

Understanding SSL Pinning

SSL pinning works by hardcoding the expected certificate (or its public key) within an application. When connecting to a server, the app checks if the presented certificate matches the pinned one. If it doesn’t, the connection is refused. Bypassing this requires finding ways to make the app accept a rogue certificate.

Steps to Bypass SSL Pinning

1. Identify Pinning Implementation: Determine how pinning is implemented in the target application. Common methods include:
   • TrustKit (iOS): A popular framework for managing trust and pinning.
   • Network Security Configuration (Android): Uses XML files to define trusted certificates.
   • Custom Code: The app may have its own code for certificate validation.

   Tools like MobSF or static analysis can help identify the pinning mechanism.

2. Check for Weak Pinning Implementations: Look for flaws in how pinning is done:
   • Incomplete Certificate Chains: If only the leaf certificate is pinned, an attacker can often obtain it and use it.
   • Pinning Only Hostname: If the app pins based on hostname instead of the full certificate, a wildcard certificate might be sufficient to bypass it.
   • Mutable Pin Sets: If the pin set can be updated dynamically without proper validation, an attacker could inject their own certificates.
3. Exploit Outdated Libraries: Older versions of SSL/TLS libraries (like OpenSSL) may have known vulnerabilities that allow certificate spoofing.
   • Heartbleed (OpenSSL): Although patched, some apps might still use vulnerable versions.
   • Logjam Attack: Exploits weak Diffie-Hellman parameters.

   Use tools like openssl version to check the library version on the target device (if possible).

   openssl version

4. Man-in-the-Middle Proxy Setup: Use a proxy tool like Burp Suite or mitmproxy to intercept and modify network traffic.
   • Configure the Proxy: Set up your device/app to use the proxy server.
   • Install Certificate: Install the proxy’s certificate as a trusted root authority on your device. This is essential for intercepting HTTPS traffic.
5. Certificate Spoofing: Generate a rogue certificate that matches the target domain.
   • Obtain Target Domain Information: Get the domain name from the app or network requests.
   • Generate Certificate: Use OpenSSL to create a self-signed certificate for the target domain:

     openssl req -x509 -newkey rsa:2048 -keyout key.pem -out cert.pem -days 365 -nodes -subj '/CN=targetdomain.com'

6. Inject Rogue Certificate (if possible): Depending on the pinning implementation, you might be able to inject the rogue certificate into the app’s trust store or modify the pin set.
   • Dynamic Pin Updates: If the app allows dynamic updates, try sending a request with your rogue certificate.
   • Root Access (Android): With root access, you can directly modify XML files containing trusted certificates in /system/etc/security/truststore.conf or similar locations.
7. Forward Traffic with the Rogue Certificate: Configure your proxy to forward traffic using the rogue certificate.
   • Burp Suite: Use Burp’s SSL settings to configure a custom certificate for the target domain.
   • mitmproxy: Configure mitmproxy to use your generated certificate when intercepting connections to the target domain.
8. Test Connection: Attempt to connect to the target application through the proxy.
   • Successful Bypass: If the connection succeeds without errors, you have successfully bypassed SSL pinning.
   • Troubleshooting: If the connection fails, review your steps and check for any configuration issues or remaining pinning checks.

Important Considerations

• Legal Implications: Bypassing SSL pinning without authorization is illegal and unethical. This guide is for educational purposes only.
• App Updates: App updates may introduce new or improved pinning mechanisms, requiring you to repeat the process.
• Cyber security best practices: Always prioritize ethical hacking and obtain explicit permission before testing any application’s security.