Xtrospy-Light analyzes what Android applications do at runtime and assist in the identification of security issues.

Xtrospy-Light comprises two separate components: a GUI interface to configure hooks, filters and options and an Xpose module containing the core of the tool functionalities, including hooks and analysis of potential issues.

Xtrospy-Light can be installed on a rooted device and dynamically configured to hook security-sensitive Android APIs at run-time. The tool records all the relevant API calls made by an application, including function calls, arguments and return values. It then perform tests for security issues in real time and persists the results in a database and in the Android logging system.

NOTE: This tool is a light version of a bigger tool that can do a lot more, but it is not planned for release at this time. Feel free to DM me on Twitter (@MarcBlanchou) for more info.

• Ensure Xposed has been deployed on your test device. The installer requires a rooted device and can be found at http://repo.xposed.info/module/de.robv.android.xposed.installer

• Install Xtrospy-Light on a device where Xposed is installed with:

    adb install Xtrospy-Light ExtCore.apk
  

• Install Xtrospy UIConfig.apk:

    adb install Xtrospy-Light UIConfig.apk
  

The Xtrospy-Light UIConfig application displays apps the Core application will hook and the various filters and options applied to them. This application need root access (you can use supersu to give temporary root access to the application). The changes are dynamic and you do not need to restard the applications for them to be effective.

• Once configured with the Config application, logs are dumped in the system logs and in a database in the directory of the application hooked (in databases/Xtrospy-Light.db)

It should be noted that the Core application can work on a device running Android 2.3 and above whereas the Config application can only run from Android 3.0 on due to the use of specific APIs. In order to test applications on older SDKs without the GUI by only using the Core application, you can simply create a file named "xtrospy.config" containing filters you want to hook in the directory of the applications you want to test. Example:

    adb shell su -c echo "GENERAL CRYPTO, KEY, HASH, FS, IPC, PREF, URI, WEBVIEW" > /data/data/com.YOUR_APP_NAME/xtrospy.config

    adb uninstall Xtrospy-Light ExtCore.apk
    adb uninstall Xtrospy-Light UIConfig.apk

This tool has not been tested on all versions of Android. If the tool does not work on your version, please send us your error logs:

    adb logcat -s “XtrospyError”

If due to the error the phone does not boot anymore, you can still connect to it via adb and simply remove the extension to fix it with:

    adb shell su -c rm /data/app/com.xtrospy.core*

• Relevant data including potential issues related to the APIs hooked is dumped in a database and in the system logs. You can do the following commands to display them:

• Display the complete logs:

    adb logcat -s "Xtrospy"
  

• Display potential issues:

    adb logcat -s "Xtrospy:W"
  

• Use the Android version of the analyzer (TBD, it will be pushed to a different github repository soon) to generate an HTML formatted report.

Checking the "STACK TRACES" option within the Config tool will dump a relevant call stack (comprising of 3 calls) for the selected filters.

• Log encrypted/decrypted data before/after calls and the algo used (Note: "readable data is displayed if at least 75% of characters are readable, unreadable characters are stored as ".". If data is not readable, it is stored as base 64)
• Spot static IVs and broken algorithms
• Spot weak RNG

• Log data that is being hashed and the resulting hash
• Display algo used and warns if weak (MD5)

• Log any keys used to encrypt
• Log PBKDF key creation (key, passcode, iterations)
• Log passcode used with a keystore

• Log only some file system accesses as they are very noisy
• Spot read/write on SD card and the creation of file (or set property) as world readable/writable

• Log IPC creations with details
• Log some Intent sent with details (and extra)
• Programmatic permissions and creation

• Log read/write of preferences with its data, the type and the default value (value set if nothing is returned)
• Dump all preferences when getAll is called, this is done only once to avoid noise
• Log world read/writeable prefs
• Warn for access to preferences that don't exist (could be a hidden preferences to enable logs for instance)

• Warn if SSL is used but any hostname is validated for a valid cert
• Warn if the app validates any cert (self-signed etc.)
• Log if cert pinning is potentially implemented
• Log if SSL not used

• Log when JS, plugins or FS access are enabled for a webview
• Warn/log when a JS interface is used (JS bridge)

• Log data passed to execSQL, update*, insert*, replace

Most users should just download and install the pre-compiled packages. However, if you want to modify the tool's functionality you will have to clone the source repository and build the packages yourself.

Adding hooks is simple and can be done within the com.xtrospy.custom_hooks module. See the pre-filled example in the code (CustomHookList.java and HookExampleImpl.java) and make sure to enable the "CUSTOM HOOKS" option in the Xtrospy Config application. See http://www.latent-io.com for more instructions.

Notes: Some methods simply cannot be hooked due to potential issues in Xposed and the hook may just crash the process. Also, make sure to not try hooking abstract methods as it just throws an exception that is never caught by Xposed (and will just crash the process). You need to hook their implementation, which is sometimes not documented but can be easily found in the Android code base (for example: android.content.Context is implemented in android.content.ContextImpl).

See ./LICENSE.

Marc Blanchou

Mathew Solnik