Bypass root + Frida

Bypass Android root protection with frida.

1. Install frida and root your emulator/device

Android Dynamic Analysis | Red Teaming and Malware Analysisgitbook.seguranca-informatica.pt

2. Use frida scripts to bypass (fast way)

Frida CodeSharecodeshare.frida.re

It works in the hardest applications. So, you need to create a file called "frida.js", and paste the code below.

Java.perform(function() {
    var RootPackages = ["com.noshufou.android.su", "com.noshufou.android.su.elite", "eu.chainfire.supersu",
        "com.koushikdutta.superuser", "com.thirdparty.superuser", "com.yellowes.su", "com.koushikdutta.rommanager",
        "com.koushikdutta.rommanager.license", "com.dimonvideo.luckypatcher", "com.chelpus.lackypatch",
        "com.ramdroid.appquarantine", "com.ramdroid.appquarantinepro", "com.devadvance.rootcloak", "com.devadvance.rootcloakplus",
        "de.robv.android.xposed.installer", "com.saurik.substrate", "com.zachspong.temprootremovejb", "com.amphoras.hidemyroot",
        "com.amphoras.hidemyrootadfree", "com.formyhm.hiderootPremium", "com.formyhm.hideroot", "me.phh.superuser",
        "eu.chainfire.supersu.pro", "com.kingouser.com"
    ];

    var RootBinaries = ["su", "busybox", "supersu", "Superuser.apk", "KingoUser.apk", "SuperSu.apk"];

    var RootProperties = {
        "ro.build.selinux": "1",
        "ro.debuggable": "0",
        "service.adb.root": "0",
        "ro.secure": "1"
    };

    var RootPropertiesKeys = [];

    for (var k in RootProperties) RootPropertiesKeys.push(k);

    var PackageManager = Java.use("android.app.ApplicationPackageManager");

    var Runtime = Java.use('java.lang.Runtime');

    var NativeFile = Java.use('java.io.File');

    var String = Java.use('java.lang.String');

    var SystemProperties = Java.use('android.os.SystemProperties');

    var BufferedReader = Java.use('java.io.BufferedReader');

    var ProcessBuilder = Java.use('java.lang.ProcessBuilder');

    var StringBuffer = Java.use('java.lang.StringBuffer');

    var loaded_classes = Java.enumerateLoadedClassesSync();

    send("Loaded " + loaded_classes.length + " classes!");

    var useKeyInfo = false;

    var useProcessManager = false;

    send("loaded: " + loaded_classes.indexOf('java.lang.ProcessManager'));

    if (loaded_classes.indexOf('java.lang.ProcessManager') != -1) {
        try {
            //useProcessManager = true;
            //var ProcessManager = Java.use('java.lang.ProcessManager');
        } catch (err) {
            send("ProcessManager Hook failed: " + err);
        }
    } else {
        send("ProcessManager hook not loaded");
    }

    var KeyInfo = null;

    if (loaded_classes.indexOf('android.security.keystore.KeyInfo') != -1) {
        try {
            //useKeyInfo = true;
            //var KeyInfo = Java.use('android.security.keystore.KeyInfo');
        } catch (err) {
            send("KeyInfo Hook failed: " + err);
        }
    } else {
        send("KeyInfo hook not loaded");
    }

    PackageManager.getPackageInfo.implementation = function(pname, flags) {
        var shouldFakePackage = (RootPackages.indexOf(pname) > -1);
        if (shouldFakePackage) {
            send("Bypass root check for package: " + pname);
            pname = "set.package.name.to.a.fake.one.so.we.can.bypass.it";
        }
        return this.getPackageInfo.call(this, pname, flags);
    };

    NativeFile.exists.implementation = function() {
        var name = NativeFile.getName.call(this);
        var shouldFakeReturn = (RootBinaries.indexOf(name) > -1);
        if (shouldFakeReturn) {
            send("Bypass return value for binary: " + name);
            return false;
        } else {
            return this.exists.call(this);
        }
    };

    var exec = Runtime.exec.overload('[Ljava.lang.String;');
    var exec1 = Runtime.exec.overload('java.lang.String');
    var exec2 = Runtime.exec.overload('java.lang.String', '[Ljava.lang.String;');
    var exec3 = Runtime.exec.overload('[Ljava.lang.String;', '[Ljava.lang.String;');
    var exec4 = Runtime.exec.overload('[Ljava.lang.String;', '[Ljava.lang.String;', 'java.io.File');
    var exec5 = Runtime.exec.overload('java.lang.String', '[Ljava.lang.String;', 'java.io.File');

    exec5.implementation = function(cmd, env, dir) {
        if (cmd.indexOf("getprop") != -1 || cmd == "mount" || cmd.indexOf("build.prop") != -1 || cmd == "id" || cmd == "sh") {
            var fakeCmd = "grep";
            send("Bypass " + cmd + " command");
            return exec1.call(this, fakeCmd);
        }
        if (cmd == "su") {
            var fakeCmd = "justafakecommandthatcannotexistsusingthisshouldthowanexceptionwheneversuiscalled";
            send("Bypass " + cmd + " command");
            return exec1.call(this, fakeCmd);
        }
        return exec5.call(this, cmd, env, dir);
    };

    exec4.implementation = function(cmdarr, env, file) {
        for (var i = 0; i < cmdarr.length; i = i + 1) {
            var tmp_cmd = cmdarr[i];
            if (tmp_cmd.indexOf("getprop") != -1 || tmp_cmd == "mount" || tmp_cmd.indexOf("build.prop") != -1 || tmp_cmd == "id" || tmp_cmd == "sh") {
                var fakeCmd = "grep";
                send("Bypass " + cmdarr + " command");
                return exec1.call(this, fakeCmd);
            }

            if (tmp_cmd == "su") {
                var fakeCmd = "justafakecommandthatcannotexistsusingthisshouldthowanexceptionwheneversuiscalled";
                send("Bypass " + cmdarr + " command");
                return exec1.call(this, fakeCmd);
            }
        }
        return exec4.call(this, cmdarr, env, file);
    };

    exec3.implementation = function(cmdarr, envp) {
        for (var i = 0; i < cmdarr.length; i = i + 1) {
            var tmp_cmd = cmdarr[i];
            if (tmp_cmd.indexOf("getprop") != -1 || tmp_cmd == "mount" || tmp_cmd.indexOf("build.prop") != -1 || tmp_cmd == "id" || tmp_cmd == "sh") {
                var fakeCmd = "grep";
                send("Bypass " + cmdarr + " command");
                return exec1.call(this, fakeCmd);
            }

            if (tmp_cmd == "su") {
                var fakeCmd = "justafakecommandthatcannotexistsusingthisshouldthowanexceptionwheneversuiscalled";
                send("Bypass " + cmdarr + " command");
                return exec1.call(this, fakeCmd);
            }
        }
        return exec3.call(this, cmdarr, envp);
    };

    exec2.implementation = function(cmd, env) {
        if (cmd.indexOf("getprop") != -1 || cmd == "mount" || cmd.indexOf("build.prop") != -1 || cmd == "id" || cmd == "sh") {
            var fakeCmd = "grep";
            send("Bypass " + cmd + " command");
            return exec1.call(this, fakeCmd);
        }
        if (cmd == "su") {
            var fakeCmd = "justafakecommandthatcannotexistsusingthisshouldthowanexceptionwheneversuiscalled";
            send("Bypass " + cmd + " command");
            return exec1.call(this, fakeCmd);
        }
        return exec2.call(this, cmd, env);
    };

    exec.implementation = function(cmd) {
        for (var i = 0; i < cmd.length; i = i + 1) {
            var tmp_cmd = cmd[i];
            if (tmp_cmd.indexOf("getprop") != -1 || tmp_cmd == "mount" || tmp_cmd.indexOf("build.prop") != -1 || tmp_cmd == "id" || tmp_cmd == "sh") {
                var fakeCmd = "grep";
                send("Bypass " + cmd + " command");
                return exec1.call(this, fakeCmd);
            }

            if (tmp_cmd == "su") {
                var fakeCmd = "justafakecommandthatcannotexistsusingthisshouldthowanexceptionwheneversuiscalled";
                send("Bypass " + cmd + " command");
                return exec1.call(this, fakeCmd);
            }
        }

        return exec.call(this, cmd);
    };

    exec1.implementation = function(cmd) {
        if (cmd.indexOf("getprop") != -1 || cmd == "mount" || cmd.indexOf("build.prop") != -1 || cmd == "id" || cmd == "sh") {
            var fakeCmd = "grep";
            send("Bypass " + cmd + " command");
            return exec1.call(this, fakeCmd);
        }
        if (cmd == "su") {
            var fakeCmd = "justafakecommandthatcannotexistsusingthisshouldthowanexceptionwheneversuiscalled";
            send("Bypass " + cmd + " command");
            return exec1.call(this, fakeCmd);
        }
        return exec1.call(this, cmd);
    };

    String.contains.implementation = function(name) {
        if (name == "test-keys") {
            send("Bypass test-keys check");
            return false;
        }
        return this.contains.call(this, name);
    };

    var get = SystemProperties.get.overload('java.lang.String');

    get.implementation = function(name) {
        if (RootPropertiesKeys.indexOf(name) != -1) {
            send("Bypass " + name);
            return RootProperties[name];
        }
        return this.get.call(this, name);
    };

    Interceptor.attach(Module.findExportByName("libc.so", "fopen"), {
        onEnter: function(args) {
            var path = Memory.readCString(args[0]);
            path = path.split("/");
            var executable = path[path.length - 1];
            var shouldFakeReturn = (RootBinaries.indexOf(executable) > -1)
            if (shouldFakeReturn) {
                Memory.writeUtf8String(args[0], "/notexists");
                send("Bypass native fopen");
            }
        },
        onLeave: function(retval) {

        }
    });

    Interceptor.attach(Module.findExportByName("libc.so", "system"), {
        onEnter: function(args) {
            var cmd = Memory.readCString(args[0]);
            send("SYSTEM CMD: " + cmd);
            if (cmd.indexOf("getprop") != -1 || cmd == "mount" || cmd.indexOf("build.prop") != -1 || cmd == "id") {
                send("Bypass native system: " + cmd);
                Memory.writeUtf8String(args[0], "grep");
            }
            if (cmd == "su") {
                send("Bypass native system: " + cmd);
                Memory.writeUtf8String(args[0], "justafakecommandthatcannotexistsusingthisshouldthowanexceptionwheneversuiscalled");
            }
        },
        onLeave: function(retval) {

        }
    });

    /*

    TO IMPLEMENT:

    Exec Family

    int execl(const char *path, const char *arg0, ..., const char *argn, (char *)0);
    int execle(const char *path, const char *arg0, ..., const char *argn, (char *)0, char *const envp[]);
    int execlp(const char *file, const char *arg0, ..., const char *argn, (char *)0);
    int execlpe(const char *file, const char *arg0, ..., const char *argn, (char *)0, char *const envp[]);
    int execv(const char *path, char *const argv[]);
    int execve(const char *path, char *const argv[], char *const envp[]);
    int execvp(const char *file, char *const argv[]);
    int execvpe(const char *file, char *const argv[], char *const envp[]);

    */


    BufferedReader.readLine.implementation = function() {
        var text = this.readLine.call(this);
        if (text === null) {
            // just pass , i know it's ugly as hell but test != null won't work :(
        } else {
            var shouldFakeRead = (text.indexOf("ro.build.tags=test-keys") > -1);
            if (shouldFakeRead) {
                send("Bypass build.prop file read");
                text = text.replace("ro.build.tags=test-keys", "ro.build.tags=release-keys");
            }
        }
        return text;
    };

    var executeCommand = ProcessBuilder.command.overload('java.util.List');

    ProcessBuilder.start.implementation = function() {
        var cmd = this.command.call(this);
        var shouldModifyCommand = false;
        for (var i = 0; i < cmd.size(); i = i + 1) {
            var tmp_cmd = cmd.get(i).toString();
            if (tmp_cmd.indexOf("getprop") != -1 || tmp_cmd.indexOf("mount") != -1 || tmp_cmd.indexOf("build.prop") != -1 || tmp_cmd.indexOf("id") != -1) {
                shouldModifyCommand = true;
            }
        }
        if (shouldModifyCommand) {
            send("Bypass ProcessBuilder " + cmd);
            this.command.call(this, ["grep"]);
            return this.start.call(this);
        }
        if (cmd.indexOf("su") != -1) {
            send("Bypass ProcessBuilder " + cmd);
            this.command.call(this, ["justafakecommandthatcannotexistsusingthisshouldthowanexceptionwheneversuiscalled"]);
            return this.start.call(this);
        }

        return this.start.call(this);
    };

    if (useProcessManager) {
        var ProcManExec = ProcessManager.exec.overload('[Ljava.lang.String;', '[Ljava.lang.String;', 'java.io.File', 'boolean');
        var ProcManExecVariant = ProcessManager.exec.overload('[Ljava.lang.String;', '[Ljava.lang.String;', 'java.lang.String', 'java.io.FileDescriptor', 'java.io.FileDescriptor', 'java.io.FileDescriptor', 'boolean');

        ProcManExec.implementation = function(cmd, env, workdir, redirectstderr) {
            var fake_cmd = cmd;
            for (var i = 0; i < cmd.length; i = i + 1) {
                var tmp_cmd = cmd[i];
                if (tmp_cmd.indexOf("getprop") != -1 || tmp_cmd == "mount" || tmp_cmd.indexOf("build.prop") != -1 || tmp_cmd == "id") {
                    var fake_cmd = ["grep"];
                    send("Bypass " + cmdarr + " command");
                }

                if (tmp_cmd == "su") {
                    var fake_cmd = ["justafakecommandthatcannotexistsusingthisshouldthowanexceptionwheneversuiscalled"];
                    send("Bypass " + cmdarr + " command");
                }
            }
            return ProcManExec.call(this, fake_cmd, env, workdir, redirectstderr);
        };

        ProcManExecVariant.implementation = function(cmd, env, directory, stdin, stdout, stderr, redirect) {
            var fake_cmd = cmd;
            for (var i = 0; i < cmd.length; i = i + 1) {
                var tmp_cmd = cmd[i];
                if (tmp_cmd.indexOf("getprop") != -1 || tmp_cmd == "mount" || tmp_cmd.indexOf("build.prop") != -1 || tmp_cmd == "id") {
                    var fake_cmd = ["grep"];
                    send("Bypass " + cmdarr + " command");
                }

                if (tmp_cmd == "su") {
                    var fake_cmd = ["justafakecommandthatcannotexistsusingthisshouldthowanexceptionwheneversuiscalled"];
                    send("Bypass " + cmdarr + " command");
                }
            }
            return ProcManExecVariant.call(this, fake_cmd, env, directory, stdin, stdout, stderr, redirect);
        };
    }

    if (useKeyInfo) {
        KeyInfo.isInsideSecureHardware.implementation = function() {
            send("Bypass isInsideSecureHardware");
            return true;
        }
    }

});

Next, after installing the target apk on your mobile device, you need to start frida server and execute the script from your attacker machine.

.\adb.exe connect localhost:21503
.\adb.exe shell '/data/local/temp/frida-server-14.2.18-android-x86 &'

frida-ps.exe -U (to obtain the app)
frida.exe -U -f 'com.xxx.xxx.xxx' -l .\frida.js --no-pause

For more details about frida, you can check the next section.

Android Dynamic Analysis | Red Teaming and Malware Analysisgitbook.seguranca-informatica.pt

3. Dynamic analysis and frida script (manual)

Many times, when the root protection is made manually, it's difficult to bypass the protection. In that scenarios, you need:

• Analyse the APK java code to understand how and where the root validation is performed

• Create a frida specially crafted script to bypass it

Souce-code analysis

To start, we can use an online decompiler like this:

Java decompiler online / APK decompiler - Decompiler.comwww.decompiler.com

or just doing it by using the tool dex2jar:

GitHub - pxb1988/dex2jar: Tools to work with android .dex and java .class filesGitHub

My favorite approach is: jadx Java decompiler:

GitHub - skylot/jadx: Dex to Java decompilerGitHub

There is also a prepared VM you can find with all the tools installed called Mobexler:

A Mobile Application Penetration Testing Platformmobexler.com

BONUS: A lot of times I use Bytecode Viewer - a lightweight user friendly Java Bytecode Viewer. This tool allow you compare the decompiled Java code using different tools, and choosing the best one for you.

After that, using the ByteCode Viewer or JADX, you can export your project (source files) and use Visual Studio Code in order to analyze the code and taking advantage of cross-references, and all the available plugins to better understand the Android code. For instance, you can also install a Java Decompiler plugin.

Finding the root validation

By using the "Search" feature, we try to get some information about where the root function is called.

and ... we got it! 😇

We can see that an object (r0) is returned if the "Device is rooted", and r0 is returned with "none" when the device is not rooted. Next, we are presenting the general block of code we analyzed.

 package d.a.a.a.c.g;
 
 (...)
 public enum g {
 (...)
   
     public static final class e extends g {
        public e(String str, int i) {
            super(str, i, (q.v.c.f) null);
        }         
        
                        
      public java.lang.Object doProcedure(android.content.Context r17, q.s.d<? super d.a.a.a.c.g.a> r18) {                                                  
              (...)   
                
              d.a.a.a.c.g.a$a r0 = d.a.a.a.c.g.a.g
                java.lang.String r2 = "Device rooted"
                d.a.a.a.c.g.a r0 = r0.a(r1, r2)
                return r0
            L_0x01ee:
                d.a.a.a.c.g.a$a r0 = d.a.a.a.c.g.a.g
                java.lang.String r2 = "none"
                d.a.a.a.c.g.a r0 = r0.a(r1, r2)
                return r0
           
               (...)
      } 
  }     

To bypass this protection, we need to:

• Create the target path: Package of the class + Add the "public enum g" + Add the target class (d.a.a.a.c.g.g$e)

• Implement the code on the target method (doProcedure)

• Create an object from "d.a.a.a.c.g.a" to return something using its constructor

We can see the constructor can be "empty" or we can passing it 5 args. Analysing the code we can understand that. For instance:

 return new d.a.a.a.c.g.a(r6, r7, r8, (android.content.DialogInterface.OnClickListener) null, 8);

Frida script (hook)

Now, it's time to write our frida script:

console.log("Starting hook ...");
Java.perform(function() {
	//package d.a.a.a.c.g;
	//d.a.a.a.c.g.g$e
	var my = Java.use("d.a.a.a.c.g.g$e");
	my.doProcedure.implementation = function (func1, func2, func3) {
		 console.log('..doing some stuff..');
		 //var x = Java.use("d.a.a.a.c.g.a").$new(); 
		 var x = Java.use("d.a.a.a.c.g.a").$new("none", "none", null, null, 8);
		 return x;
	}
});

another approach overloading the method:

Java.perform(function () {

	var hookclass = Java.use("d.a.a.a.c.g.g$e");

	hookclass.doProcedure.overload("android.content.Context", "q.s.d").implementation = function(ctx, rsd) {
		var p = Java.use("d.a.a.a.c.g.a").$new("none", "none", null, null, 8);
		var ret = p;
		console.log(ret);
		return ret;
	}
	console.log("hook created!");
});

To execute it:

.\adb.exe connect localhost:21503
.\adb.exe shell '/data/local/temp/frida-server-14.2.18-android-x86 &'

frida.exe -U -f 'com.xxx.xxx.xxxx' -l .\frida.js --no-pause

and, we got it! We bypassed root validations!😎

BONUS - PATCH the APK

Instead using frida, we can patch directly the APK using this approach:

Backdooring/patch APKs | Red Teaming and Malware Analysisgitbook.seguranca-informatica.pt

So, we just need, in this case, changing the content of the r2 (v2 smali) variable.

Before

After

After that, we need to follow the steps to build the APK, sign it and align it. 😎