Using Frida to bypass certificate pinning

Using Frida to bypass certificate pinning

Often the TLS negotation fails for Android applications when you try to intercept the HTTP(S) traffic. A network capture trace can give you a good indication of certificate pinning is in place. Frida makes it possible to manipulate the application in runtime, very helpful when trying to bypass SSL pinning.

Tools requirements

• Python3
• Objection
• Frida
• Android Studio

Tools installation procedure

• Step 1: Download latest version of python3 and install it. Make sure to tab enable path environment as well.
• Step 2: Install Objection using pip3. (pip3 install objection) Note: Frida is a pre-requisite for objection, hence frida will get installed automatically.
• Step 3: Download and install latest version of Android studio (https://developer.android.com/studio).
• Step 4: Download any Android images (above 7.0) for the emulator.
• Step 5: Download the Android SDK Platform-Tools (adb) (https://dl.google.com/android/repository/platform-tools-latest-windows.zip).

Injection script

Download the injection script from below which will be pushed into the device for injecting into the target application. https://codeshare.frida.re/@pcipolloni/universal-android-ssl-pinning-bypass-with-frida/ Or copy and save this code as frida.js in same folder as adb.

/* 
   Android SSL Re-pinning frida script v0.2 030417-pier 

   $ adb push burpca-cert-der.crt /data/local/tmp/cert-der.crt
   $ frida -U -f it.app.mobile -l frida-android-repinning.js --no-pause

   https://techblog.mediaservice.net/2017/07/universal-android-ssl-pinning-bypass-with-frida/
   
   UPDATE 20191605: Fixed undeclared var. Thanks to @oleavr and @ehsanpc9999 !
*/

setTimeout(function(){
    Java.perform(function (){
        console.log("");
        console.log("[.] Cert Pinning Bypass/Re-Pinning");

        var CertificateFactory = Java.use("java.security.cert.CertificateFactory");
        var FileInputStream = Java.use("java.io.FileInputStream");
        var BufferedInputStream = Java.use("java.io.BufferedInputStream");
        var X509Certificate = Java.use("java.security.cert.X509Certificate");
        var KeyStore = Java.use("java.security.KeyStore");
        var TrustManagerFactory = Java.use("javax.net.ssl.TrustManagerFactory");
        var SSLContext = Java.use("javax.net.ssl.SSLContext");

        // Load CAs from an InputStream
        console.log("[+] Loading our CA...")
        var cf = CertificateFactory.getInstance("X.509");
        
        try {
            var fileInputStream = FileInputStream.$new("/data/local/tmp/cert-der.crt");
        }
        catch(err) {
            console.log("[o] " + err);
        }
        
        var bufferedInputStream = BufferedInputStream.$new(fileInputStream);
        var ca = cf.generateCertificate(bufferedInputStream);
        bufferedInputStream.close();

        var certInfo = Java.cast(ca, X509Certificate);
        console.log("[o] Our CA Info: " + certInfo.getSubjectDN());

        // Create a KeyStore containing our trusted CAs
        console.log("[+] Creating a KeyStore for our CA...");
        var keyStoreType = KeyStore.getDefaultType();
        var keyStore = KeyStore.getInstance(keyStoreType);
        keyStore.load(null, null);
        keyStore.setCertificateEntry("ca", ca);
        
        // Create a TrustManager that trusts the CAs in our KeyStore
        console.log("[+] Creating a TrustManager that trusts the CA in our KeyStore...");
        var tmfAlgorithm = TrustManagerFactory.getDefaultAlgorithm();
        var tmf = TrustManagerFactory.getInstance(tmfAlgorithm);
        tmf.init(keyStore);
        console.log("[+] Our TrustManager is ready...");

        console.log("[+] Hijacking SSLContext methods now...")
        console.log("[-] Waiting for the app to invoke SSLContext.init()...")

        SSLContext.init.overload("[Ljavax.net.ssl.KeyManager;", "[Ljavax.net.ssl.TrustManager;", "java.security.SecureRandom").implementation = function(a,b,c) {
            console.log("[o] App invoked javax.net.ssl.SSLContext.init...");
            SSLContext.init.overload("[Ljavax.net.ssl.KeyManager;", "[Ljavax.net.ssl.TrustManager;", "java.security.SecureRandom").call(this, a, tmf.getTrustManagers(), c);
            console.log("[+] SSLContext initialized with our custom TrustManager!");
        }
    });
},0);

Frida server

Download frida server for supported android device’s architecture version. To find the architecture version run the command:

adb shell getprop ro.product.cpu.abi

Now go to the download page: https://github.com/frida/frida/releases/ and choose the appropriate version. For example, if your architecture version is x86, you must download: frida-server-16.0.8-android-x86.xz.

Now extract the xz file and move frida-server file to the Android device.

adb push C:\xyz\frida-server-16.0.8-android-x86 /data/local/tmp/frida-server
adb shell chmod 777 /data/local/tmp/frida-server

configure Android device to work with Burp

Follow the guide to configure configure an Android device to work with Burp https://portswigger.net/burp/documentation/desktop/mobile/config-android-device

The exported certificate can be pushed

adb push cacert.der /data/local/tmp/cert-der.crt

Start Frida

Copy the frida.js script to the Android device by using the command

adb push C:\xyz\frida.js /data/local/tmp

Start now Frida

adb shell /data/local/tmp/frida-server &

Now check if Frida is running and get a list of running processes:

frida-ps -U

Copy the application name of the applicatoin you want to MiTM from the output above.

Start now the application and ssl pinning bypass:

frida -U -f <your_application_package_name> -l <path_to_fridascript.js_on_your_computer> 

Note: work in progress. Still working on finishing this article/post.