Android Web View Security: A Practical Guide

TL;DR

Web Views in Android let your app display web content, but they can be a security risk if not handled carefully. This guide shows you how to make them much safer by controlling what they can do and keeping everything updated.

Improving Web View Security: Step-by-Step

1. Understand the Risks
   • Cross-Site Scripting (XSS): Malicious websites loaded in a Web View could run harmful code.
   • JavaScript Injection: Attackers might inject JavaScript to steal data or control your app.
   • File Access: Web Views can potentially access files on the device if permissions aren’t restricted.
   • Network Security: Insecure connections (HTTP instead of HTTPS) expose data during transmission.
2. Enable JavaScript Only When Needed

   Only turn on JavaScript if your Web View absolutely requires it. If not, disable it.

   webView.getSettings().setJavaScriptEnabled(false);

3. Control Allowed URLs

   Restrict the Web View to only load content from trusted domains. Use a WebChromeClient and override shouldOverrideUrlLoading().

   class MyWebChromeClient extends WebChromeClient {
       @Override
       public boolean shouldOverrideUrlLoading(WebView view, String url) {
           if (url.startsWith("https://yourtrusteddomain.com/")) {
               return false; // Allow loading
           } else {
               return true; // Prevent loading
           }
       }
   }
   webView.setWebChromeClient(new MyWebChromeClient());

4. Handle URL Schemes Carefully

   Be very cautious about custom URL schemes (like mailto: or your own app-specific schemes). Validate them thoroughly before allowing them to open.

5. Disable File Access

   Prevent the Web View from accessing local files unless absolutely necessary. Use these settings:

   • webView.getSettings().setAllowFileAccess(false);
   • webView.getSettings().setAllowContentAccess(false);
6. Secure Network Connections (HTTPS)

   Always load content over HTTPS. Consider using HSTS (HTTP Strict Transport Security) if possible.

   • Check that all URLs loaded in the Web View start with https://.
7. Implement a SafeBridge for JavaScript Communication

   If you need to call JavaScript code from your app (or vice versa), create a secure bridge instead of directly exposing methods.

   • Use addJavascriptInterface() with caution.
   • Annotate the interface with @JavascriptInterface.
   • Validate all input and output carefully to prevent injection attacks.
8. Regularly Update Web View Components

   Keep your Android SDK and Chrome (the underlying engine for Web Views) up-to-date. Updates often include important security fixes.

9. Use Content Security Policy (CSP)

   If you control the web content being loaded, implement a strong CSP to restrict what resources the page can load and execute.

10. Monitor for Vulnerabilities

    Stay informed about known Web View vulnerabilities and apply patches promptly. Regularly scan your app’s dependencies for security issues.