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Tapjacking

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Basic Information

Tapjacking is an attack where a malicious application is launched and positions itself on top of a victim application. Once it visibly obscures the victim app, its user interface is designed in such a way as to trick the user to interact with it, while it is passing the interaction along to the victim app. In effect, it is blinding the user from knowing they are actually performing actions on the victim app.

Detection

In order to detect apps vulnerable to this attacked you should search for exported activities in the android manifest (note that an activity with an intent-filter is automatically exported by default). Once you have found the exported activities, check if they require any permission. This is because the malicious application will need that permission also.

Protection

Android 12 (API 31,32) and higher

According to this source, tapjacking attacks are automatically prevented by Android from Android 12 (API 31 & 30) and higher. So, even if the application is vulnerable you won't be able to exploit it.

filterTouchesWhenObscured

If android:filterTouchesWhenObscured is set to true, the View will not receive touches whenever view's window is obscured by another visible window.

setFilterTouchesWhenObscured

The attribute setFilterTouchesWhenObscured set to true can also prevent the exploitation of this vulnerability if the Android version is lower. If set to true, for example, a button can be automatically disabled if it is obscured:

<Button android:text="Button"
android:id="@+id/button1"
android:layout_width="wrap_content"
android:layout_height="wrap_content" 
android:filterTouchesWhenObscured="true">
</Button>

Exploitation

Tapjacking-ExportedActivity

The most recent Android application performing a Tapjacking attack (+ invoking before an exported activity of the attacked application) can be found in: https://github.com/carlospolop/Tapjacking-ExportedActivity.

Follow the README instructions to use it.

FloatingWindowApp

An example project implementing FloatingWindowApp, which can be used to put on top of other activities to perform a clickjacking attack, can be fund in FloatingWindowApp (a bit old, good luck building the apk).

Qark

It looks like this project is now unmaintained and this functionality isn't properly working anymore

You can use qark with the --exploit-apk --sdk-path /Users/username/Library/Android/sdk parameters to create a malicious application to test for possible Tapjacking vulnerabilities.\

The mitigation is relatively simple as the developer may choose not to receive touch events when a view is covered by another. Using the Android Developer’s Reference:

Sometimes it is essential that an application be able to verify that an action is being performed with the full knowledge and consent of the user, such as granting a permission request, making a purchase or clicking on an advertisement. Unfortunately, a malicious application could try to spoof the user into performing these actions, unaware, by concealing the intended purpose of the view. As a remedy, the framework offers a touch filtering mechanism that can be used to improve the security of views that provide access to sensitive functionality.

To enable touch filtering, call setFilterTouchesWhenObscured(boolean) or set the android:filterTouchesWhenObscured layout attribute to true. When enabled, the framework will discard touches that are received whenever the view's window is obscured by another visible window. As a result, the view will not receive touches whenever a toast, dialog or other window appears above the view's window.

LogoWebsec | Uw Cybersecurity Specialist
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