feat(android): Introduce setSupportMultipleWindows to mitigate CVE-2020-6506 (#1747 by @mrcoinbase and @kelset -- THANK YOU!)

BREAKING CHANGE:

This release introduces the `setSupportMultipleWindows` prop for Android. This sets the underlying Android WebView setting `setSupportMultipleWindows`. This prop defaults to `true` (previously `false`), and serves to mitigate the security advisory [CVE-2020-6506](https://github.com/react-native-webview/react-native-webview/security/advisories/GHSA-36j3-xxf7-4pqg).

The primary way this new behavior changes existing React Native WebView implementations on Android is that links that open in new tabs/windows (such as `<a target="_blank">`) will now prompt to open in the system browser, rather than re-using the current WebView.

If this behavior is not desirable, you can set this new prop to `false`, but be aware that this exposes your app to the security vulnerability listed above. Make sure you have read and understand the whole advisory and relevant links.

iOS & Windows are unaffected.

```jsx
<WebView
  // ...
  setSupportMultipleWindows={true} // default: true
/>
```

Thanks to @mrcoinbase, @kelset, and @Titozzz for their work on this.

android/src/main/java/com/reactnativecommunity/webview/RNCWebViewManager.java

@@ -13,6 +13,7 @@ import android.net.http.SslError;
 import android.net.Uri;
 import android.os.Build;
 import android.os.Environment;
+import android.os.Message;
 import android.os.SystemClock;
 import android.text.TextUtils;
 import android.util.Log;
@@ -187,6 +188,7 @@ public class RNCWebViewManager extends SimpleViewManager<WebView> {
     settings.setBuiltInZoomControls(true);
     settings.setDisplayZoomControls(false);
     settings.setDomStorageEnabled(true);
+    settings.setSupportMultipleWindows(true);
 
     settings.setAllowFileAccess(false);
     settings.setAllowContentAccess(false);
@@ -252,6 +254,11 @@ public class RNCWebViewManager extends SimpleViewManager<WebView> {
     view.getSettings().setJavaScriptEnabled(enabled);
   }
 
+  @ReactProp(name = "setSupportMultipleWindows")
+  public void setSupportMultipleWindows(WebView view, boolean enabled){
+    view.getSettings().setSupportMultipleWindows(enabled);
+  }
+
   @ReactProp(name = "showsHorizontalScrollIndicator")
   public void setShowsHorizontalScrollIndicator(WebView view, boolean enabled) {
     view.setHorizontalScrollBarEnabled(enabled);
@@ -875,7 +882,7 @@ public class RNCWebViewManager extends SimpleViewManager<WebView> {
         // This is desired behavior. We later use these values to determine whether the request is a top-level navigation or a subresource request.
         String topWindowUrl = webView.getUrl();
         String failingUrl = error.getUrl();
-        
+
         // Cancel request after obtaining top-level URL.
         // If request is cancelled before obtaining top-level URL, undesired behavior may occur.
         // Undesired behavior: Return value of WebView.getUrl() may be the current URL instead of the failing URL.
@@ -1073,6 +1080,17 @@ public class RNCWebViewManager extends SimpleViewManager<WebView> {
       this.mWebView = webView;
     }
 
+    @Override
+    public boolean onCreateWindow(WebView view, boolean isDialog, boolean isUserGesture, Message resultMsg) {
+
+      final WebView newWebView = new WebView(view.getContext());
+      final WebView.WebViewTransport transport = (WebView.WebViewTransport) resultMsg.obj;
+      transport.setWebView(newWebView);
+      resultMsg.sendToTarget();
+
+      return true;
+    }
+
     @Override
     public boolean onConsoleMessage(ConsoleMessage message) {
       if (ReactBuildConfig.DEBUG) {

docs/Reference.md

@@ -72,6 +72,7 @@ This document lays out the current public properties and methods for the React N
 - [`ignoreSilentHardwareSwitch`](Reference.md#ignoreSilentHardwareSwitch)
 - [`onFileDownload`](Reference.md#onFileDownload)
 - [`autoManageStatusBarEnabled`](Reference.md#autoManageStatusBarEnabled)
+- [`setSupportMultipleWindows`](Reference.md#setSupportMultipleWindows)
 
 ## Methods Index
 
@@ -782,7 +783,7 @@ A Boolean value indicating whether JavaScript can open windows without user inte
 
 ### `androidHardwareAccelerationDisabled`[⬆](#props-index)<!-- Link generated with jump2header -->
 
-**Deprecated.** Use the `androidLayerType` prop instead. 
+**Deprecated.** Use the `androidLayerType` prop instead.
 
 | Type | Required | Platform |
 | ---- | -------- | -------- |
@@ -792,7 +793,7 @@ A Boolean value indicating whether JavaScript can open windows without user inte
 
 ### `androidLayerType`[⬆](#props-index)<!-- Link generated with jump2header -->
 
-Specifies the layer type. 
+Specifies the layer type.
 
 Possible values for `androidLayerType` are:
 
@@ -1282,6 +1283,21 @@ Example:
 <WebView autoManageStatusBarEnabled={false} />
 ```
 
+### `setSupportMultipleWindows`
+
+Sets whether the WebView supports multiple windows. See [Android documentation]('https://developer.android.com/reference/android/webkit/WebSettings#setSupportMultipleWindows(boolean)') for more information.
+Setting this to false can expose the application to this [vulnerability](https://alesandroortiz.com/articles/uxss-android-webview-cve-2020-6506/) allowing a malicious iframe to escape into the top layer DOM.
+
+| Type    | Required | Default | Platform |
+| ------- | -------- | ------- | -------- |
+| boolean | No       | true    | Android  |
+
+Example:
+
+```javascript
+<WebView setSupportMultipleWindows={false} />
+```
+
 ## Methods
 
 ### `extraNativeComponentConfig()`[⬆](#methods-index)<!-- Link generated with jump2header -->

example/App.tsx

@@ -18,6 +18,7 @@ import Uploads from './examples/Uploads';
 import Injection from './examples/Injection';
 import LocalPageLoad from './examples/LocalPageLoad';
 import Messaging from './examples/Messaging';
+import NativeWebpage from './examples/NativeWebpage';
 
 const TESTS = {
   Messaging: {
@@ -84,6 +85,14 @@ const TESTS = {
       return <LocalPageLoad />;
     },
   },
+  NativeWebpage: {
+    title: 'NativeWebpage',
+    testId: 'NativeWebpage',
+    description: 'Test to open a new webview with a link',
+    render() {
+      return <NativeWebpage />;
+    },
+  },
 };
 
 type Props = {};
@@ -166,6 +175,11 @@ export default class App extends Component<Props, State> {
             title="Messaging"
             onPress={() => this._changeTest('Messaging')}
           />
+          <Button
+            testID="testType_nativeWebpage"
+            title="NativeWebpage"
+            onPress={() => this._changeTest('NativeWebpage')}
+          />
         </View>
 
         {restarting ? null : (

example/examples/NativeWebpage.tsx

@@ -0,0 +1,23 @@
+import React, {Component} from 'react';
+import {View} from 'react-native';
+
+import WebView from 'react-native-webview';
+
+type Props = {};
+type State = {};
+
+export default class NativeWebpage extends Component<Props, State> {
+  state = {};
+
+  render() {
+    return (
+      <View style={{height: 400}}>
+        <WebView
+          source={{uri: 'https://infinite.red'}}
+          style={{width: '100%', height: '100%'}}
+          // setSupportMultipleWindows={false}
+        />
+      </View>
+    );
+  }
+}

src/WebView.android.tsx

@@ -63,6 +63,7 @@ class WebView extends React.Component<AndroidWebViewProps, State> {
     androidHardwareAccelerationDisabled: false,
     androidLayerType: 'none',
     originWhitelist: defaultOriginWhitelist,
+    setSupportMultipleWindows: true,
   };
 
   static isFileUploadSupported = async () => {

src/WebViewTypes.ts

@@ -295,6 +295,7 @@ export interface AndroidNativeWebViewProps extends CommonNativeWebViewProps {
   onRenderProcessGone?: (event: WebViewRenderProcessGoneEvent) => void;
   overScrollMode?: OverScrollModeType;
   saveFormDataDisabled?: boolean;
+  setSupportMultipleWindows?: boolean;
   textZoom?: number;
   thirdPartyCookiesEnabled?: boolean;
   messagingModuleName?: string;
@@ -799,6 +800,13 @@ export interface AndroidWebViewProps extends WebViewSharedProps {
    */
   saveFormDataDisabled?: boolean;
 
+  /**
+   * Boolean value to set whether the WebView supports multiple windows. Used on Android only
+   * The default value is `true`.
+   * @platform android
+   */
+  setSupportMultipleWindows?: boolean;
+
   /**
    * Used on Android only, controls whether the given list of URL prefixes should
    * make {@link com.facebook.react.views.webview.ReactWebViewClient} to launch a