# Bypass Biometric Authentication (Android)

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These methods were copied from [https://securitycafe.ro/2022/09/05/mobile-pentesting-101-bypassing-biometric-authentication/](https://securitycafe.ro/2022/09/05/mobile-pentesting-101-bypassing-biometric-authentication/)

## **Method 1 – When the crypto object is not used**

The authentication implementation relies on the callback _**onAuthenticationSucceded** _ being called. The researchers from F-Secure developed a [**Frida script**](https://github.com/FSecureLABS/android-keystore-audit/blob/master/frida-scripts/fingerprint-bypass.js) that can be used to **bypass** the NULL _**CryptoObject** _ in _**onAuthenticationSucceeded(…)**_. The script will automatically bypass the fingerprint when the aforementioned method is called. Here is a short example that shows the bypass for the Android Fingerprint. The complete application can be downloaded from my [GitHub](https://github.com/St3v3nsS/InsecureBanking).

```javascript
biometricPrompt = new BiometricPrompt(this, executor, new BiometricPrompt.AuthenticationCallback() {
            @Override
            public void onAuthenticationSucceeded(@NonNull BiometricPrompt.AuthenticationResult result) {
                Toast.makeText(MainActivity.this,"Success",Toast.LENGTH_LONG).show();
            }
});
```

```
frida -U -f com.st3v3nss.insecurebankingfingerprint --no-pause -l fingerprint-bypass.js
```

### **Method 2 – Exception Handling**

This [**Frida script**](https://github.com/FSecureLABS/android-keystore-audit/blob/master/frida-scripts/fingerprint-bypass-via-exception-handling.js) developed by F-Secure can be used to bypass the insecure usage of the crypto object. All the script needs to do is manually call the _**onAuthenticationSucceded**_ with a **non-authorized** (not unlocked by fingerprint) _**CryptoObject**_ stored in the Keystore. The catch is if the application will attempt to use another cipher object, then an **exception will be thrown**. This script will attempt to call _**onAuthenticationSucceded** _ and catch the exception _**javax.crypto.IllegalBlockSizeException**_ in _Cipher_ class. From now on, **any objects the application uses will be encrypted using this new key**.

```
frida -U -f com.st3v3nss.insecurebankingfingerprint --no-pause -l fingerprint-bypass-via-exception-handling.js
```

Now, go to the fingerprint screen and wait for the _authenticate_() to be called. Once you see that on the screen, go ahead and type _**bypass()**_ in the Frida console:

```
Spawning `com.st3v3nss.insecurebankingfingerprint`...                   
[Android Emulator 5554::com.st3v3nss.insecurebankingfingerprint ]-> Hooking BiometricPrompt.authenticate()...
Hooking BiometricPrompt.authenticate2()...
Hooking FingerprintManager.authenticate()...
[Android Emulator 5554::com.st3v3nss.insecurebankingfingerprint ]-> bypass()
```

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