• Platform: Android
• Weakness: MASWE-0034
• Weakness in the numbering of the MASWE beta: MASWE-0069
• Profiles: L1 (basic security), L2 (advanced security)
• Type: static, code, manual
• Prerequisites: identify-security-relevant-contexts
• Knowledge: MASTG-KNOW-0018
• Best practices: MASTG-BEST-0011, MASTG-BEST-0012, MASTG-BEST-0013, MASTG-BEST-0035

Overview

This test verifies Android apps that use WebViews with legacy WebView-Native bridges do not expose native code to websites loaded inside the WebView.

These bridges are created by registering a Java object with the WebView through addJavascriptInterface. Public methods of that object that are annotated with @JavascriptInterface become callable from JavaScript running inside the WebView, using the provided name as the global JavaScript object.

For this mechanism to work, JavaScript execution must be enabled on the WebView by calling WebSettings.setJavaScriptEnabled(true)) (default is false), since the exposed interface is invoked from JavaScript code executed within the page.

Steps

1. Use MASTG-TECH-0013 to reverse engineer the app.
2. Use MASTG-TECH-0014 to look for the relevant APIs.

Observation

The output should contain any references to the relevant WebView APIs.

Evaluation

The test case fails if all the following are true:

• setJavaScriptEnabled is explicitly set to true.
• addJavascriptInterface is used at least once.
• At least one method annotated with @JavascriptInterface handles sensitive data or actions and is reachable from untrusted content.

Further Validation Required:

Inspect each reported code location using MASTG-TECH-0023 to determine whether the bridge is used in a security-relevant context:

• Determine whether the exposed methods handle sensitive data or security-critical actions.
• Determine whether the bridge is reachable from untrusted content, for example if the WebView can load arbitrary or weakly validated URLs, or if the app does not implement proper origin allowlisting.

Well-known Challenges when testing for WebView-Native bridges:

• The app may use parametrized or indirect calls to these APIs, for example through utility methods or wrapper classes. Static analysis may not be able to resolve these calls, and dynamic analysis may require specific app states or user interactions to trigger them.
• The app may use several WebViews with different configurations, and it may be difficult to determine which values are set for each WebView instance, especially if they are created dynamically, in different code paths or even across different files.
• The app may use obfuscation, reflection, or dynamic code loading to hide the use of these APIs.

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