Protection of intentURL attack using interactive dialog confirmation

app/src/main/AndroidManifest.xml

@@ -67,6 +67,10 @@
                 <data android:mimeType="text/plain" />
             </intent-filter>
         </activity>
+        <activity
+            android:name=".messages.IntentUrlDialogActivity"
+            android:exported="false"
+            android:theme="@style/AppTheme.Dialog" />
 
         <service android:name=".service.WebSocketService" />
 

app/src/main/kotlin/com/github/gotify/messages/IntentUrlDialogActivity.kt

@@ -0,0 +1,33 @@
+package com.github.gotify.messages
+
+import android.content.Intent
+import android.net.Uri
+import android.os.Bundle
+import androidx.appcompat.app.AppCompatActivity
+import com.github.gotify.databinding.ActivityDialogIntentUrlBinding
+
+internal class IntentUrlDialogActivity : AppCompatActivity() {
+    override fun onCreate(savedInstanceState: Bundle?) {
+        super.onCreate(savedInstanceState)
+        setFinishOnTouchOutside(false)
+        val binding = ActivityDialogIntentUrlBinding.inflate(layoutInflater)
+        val intentUrl = intent.getStringExtra(EXTRA_KEY_URL)
+        assert(intentUrl != null) { "intentUrl may not be empty" }
+
+        binding.urlView.text = intentUrl
+        binding.openButton.setOnClickListener {
+            finish()
+            Intent(Intent.ACTION_VIEW).apply {
+                data = Uri.parse(intentUrl)
+                flags = Intent.FLAG_ACTIVITY_NEW_TASK
+                startActivity(this)
+            }
+        }
+        binding.cancelButton.setOnClickListener { finish() }
+        setContentView(binding.root)
+    }
+
+    companion object {
+        const val EXTRA_KEY_URL = "url"
+    }
+}

app/src/main/kotlin/com/github/gotify/service/WebSocketService.kt

@@ -31,6 +31,7 @@ import com.github.gotify.client.model.Message
 import com.github.gotify.log.Log
 import com.github.gotify.log.UncaughtExceptionHandler
 import com.github.gotify.messages.Extras
+import com.github.gotify.messages.IntentUrlDialogActivity
 import com.github.gotify.messages.MessagesActivity
 import com.github.gotify.picasso.PicassoHandler
 import io.noties.markwon.Markwon
@@ -320,9 +321,10 @@ internal class WebSocketService : Service() {
         )
 
         if (intentUrl != null) {
-            intent = Intent(Intent.ACTION_VIEW)
-            intent.data = Uri.parse(intentUrl)
-            intent.flags = Intent.FLAG_ACTIVITY_NEW_TASK
+            intent = Intent(this, IntentUrlDialogActivity::class.java).apply {
+                putExtra(IntentUrlDialogActivity.EXTRA_KEY_URL, intentUrl)
+                flags = Intent.FLAG_ACTIVITY_NEW_TASK
+            }
             startActivity(intent)
         }
 

app/src/main/kotlin/com/github/gotify/settings/SettingsActivity.kt

@@ -5,8 +5,10 @@ import android.content.DialogInterface
 import android.content.Intent
 import android.content.SharedPreferences
 import android.content.SharedPreferences.OnSharedPreferenceChangeListener
+import android.net.Uri
 import android.os.Build
 import android.os.Bundle
+import android.provider.Settings
 import android.view.MenuItem
 import android.view.View
 import androidx.appcompat.app.AppCompatActivity
@@ -97,6 +99,14 @@ internal class SettingsActivity : AppCompatActivity(), OnSharedPreferenceChangeL
                     Utils.setExcludeFromRecent(requireContext(), value as Boolean)
                     return@OnPreferenceChangeListener true
                 }
+            findPreference<SwitchPreferenceCompat>(
+                getString(R.string.setting_key_intent_dialog_permission)
+            )?.let {
+                it.setOnPreferenceChangeListener { _, _ ->
+                    openSystemAlertWindowPermissionPage()
+                }
+            }
+            checkSystemAlertWindowPermission()
         }
 
         override fun onDisplayPreferenceDialog(preference: Preference) {
@@ -107,6 +117,35 @@ internal class SettingsActivity : AppCompatActivity(), OnSharedPreferenceChangeL
             }
         }
 
+        override fun onResume() {
+            super.onResume()
+            checkSystemAlertWindowPermission()
+        }
+
+        private fun openSystemAlertWindowPermissionPage(): Boolean {
+            Intent(
+                Settings.ACTION_MANAGE_OVERLAY_PERMISSION,
+                Uri.parse("package:${requireContext().packageName}")
+            ).apply {
+                startActivity(this)
+            }
+            return true
+        }
+
+        private fun checkSystemAlertWindowPermission() {
+            findPreference<SwitchPreferenceCompat>(
+                getString(R.string.setting_key_intent_dialog_permission)
+            )?.let {
+                val canDrawOverlays = Settings.canDrawOverlays(requireContext())
+                it.isChecked = canDrawOverlays
+                it.summary = if (canDrawOverlays) {
+                    getString(R.string.setting_summary_intent_dialog_permission_granted)
+                } else {
+                    getString(R.string.setting_summary_intent_dialog_permission)
+                }
+            }
+        }
+
         private fun showListPreferenceDialog(preference: ListPreference) {
             val dialogFragment = MaterialListPreference()
             dialogFragment.arguments = Bundle(1).apply { putString("key", preference.key) }

app/src/main/res/layout/activity_dialog_intent_url.xml

@@ -0,0 +1,52 @@
+<?xml version="1.0" encoding="utf-8"?>
+<LinearLayout
+    xmlns:android="http://schemas.android.com/apk/res/android"
+    xmlns:tools="http://schemas.android.com/tools"
+    android:layout_width="match_parent"
+    android:layout_height="match_parent"
+    android:maxWidth="560dp"
+    android:minWidth="280dp"
+    android:orientation="vertical"
+    android:padding="24dp">
+
+    <com.google.android.material.textview.MaterialTextView
+        android:id="@+id/message_view"
+        android:layout_width="wrap_content"
+        android:layout_height="wrap_content"
+        android:text="@string/action_dialog_message"
+        android:textSize="18sp" />
+
+    <com.google.android.material.textview.MaterialTextView
+        android:id="@+id/url_view"
+        android:layout_width="wrap_content"
+        android:layout_height="wrap_content"
+        android:gravity="center_horizontal"
+        android:layout_gravity="center_horizontal"
+        android:layout_marginTop="8dp"
+        android:textSize="18sp"
+        android:textStyle="italic"
+        tools:text="https://gotify.net" />
+
+    <LinearLayout
+        android:layout_width="wrap_content"
+        android:layout_height="wrap_content"
+        android:layout_gravity="end"
+        android:layout_marginTop="24dp">
+
+        <com.google.android.material.button.MaterialButton
+            style="@style/Widget.Material3.Button.TextButton.Dialog"
+            android:id="@+id/cancel_button"
+            android:layout_width="wrap_content"
+            android:layout_height="wrap_content"
+            android:text="@string/action_dialog_button_cancel" />
+
+        <com.google.android.material.button.MaterialButton
+            style="@style/Widget.Material3.Button.TextButton.Dialog"
+            android:id="@+id/open_button"
+            android:layout_width="wrap_content"
+            android:layout_height="wrap_content"
+            android:text="@string/action_dialog_button_open" />
+
+    </LinearLayout>
+
+</LinearLayout>

app/src/main/res/values/strings.xml

@@ -86,6 +86,10 @@
     <string name="setting_key_notification_channels">notification_channels</string>
     <string name="setting_key_exclude_from_recent">exclude_from_recent</string>
     <string name="setting_exclude_from_recent">Exclude from recents</string>
+    <string name="setting_intent_dialog_permission">Intent Action Permission</string>
+    <string name="setting_key_intent_dialog_permission">intent_dialog_permission</string>
+    <string name="setting_summary_intent_dialog_permission">To always show incoming intent URLs, give permission to show this app on top of other apps.</string>
+    <string name="setting_summary_intent_dialog_permission_granted">Permission granted.</string>
     <string name="push_message">Push message</string>
     <string name="appListDescription">App:</string>
     <string name="priorityDescription">Priority:</string>
@@ -96,6 +100,10 @@
     <string name="push_missing_app_info">There are no applications available on the server to push a message to.</string>
     <string name="message_copied_to_clipboard">Content copied to clipboard</string>
     <string name="not_loggedin_share">Cannot share to Gotify, because you aren\'t logged in.</string>
+    <string name="action_dialog_missing">Missing URL</string>
+    <string name="action_dialog_message">You have received a message with an intent url:</string>
+    <string name="action_dialog_button_open">Open</string>
+    <string name="action_dialog_button_cancel">Cancel</string>
 
     <string name="websocket_not_connected">Not connected</string>
     <string name="websocket_reconnect">Trying to reconnect</string>

app/src/main/res/values/styles.xml

@@ -39,6 +39,12 @@
 
     <style name="AppTheme.PopupOverlay" parent="AppTheme" />
 
+    <style name="AppTheme.Dialog" parent="Theme.Material3.DayNight.Dialog">
+        <item name="colorPrimary">@color/colorPrimary</item>
+        <item name="colorPrimaryDark">@color/colorPrimaryDark</item>
+        <item name="colorAccent">@color/colorAccent</item>
+    </style>
+
     <style name="Preference.SwitchPreferenceCompat" parent="@style/Preference.SwitchPreferenceCompat.Material" tools:ignore="ResourceCycle">
         <item name="widgetLayout">@layout/preference_switch</item>
     </style>

app/src/main/res/xml/root_preferences.xml

@@ -1,5 +1,6 @@
 <PreferenceScreen xmlns:android="http://schemas.android.com/apk/res/android"
-    xmlns:app="http://schemas.android.com/apk/res-auto">
+    xmlns:app="http://schemas.android.com/apk/res-auto"
+    xmlns:tools="http://schemas.android.com/tools">
 
     <PreferenceCategory app:title="@string/settings_appearance" >
         <ListPreference
@@ -37,6 +38,11 @@
             android:key="@string/setting_key_notification_channels"
             android:title="@string/setting_notification_channels"
             app:singleLineTitle="false" />
+
+        <SwitchPreferenceCompat
+            android:key="@string/setting_key_intent_dialog_permission"
+            android:title="@string/setting_intent_dialog_permission"
+            tools:summary="@string/setting_summary_intent_dialog_permission" />
     </PreferenceCategory>
 
 </PreferenceScreen>