• Platform: Android
• Weakness: MASWE-0035
• Weakness in the numbering of the MASWE beta: MASWE-0071
• Profiles: L1 (basic security), L2 (advanced security)
• Type: static, code, manual
• APIs: WebView, WebViewClient, shouldOverrideUrlLoading, shouldInterceptRequest, setWebViewClient
• Knowledge: MASTG-KNOW-0018

Overview

This test checks for references to WebViewClient URL interception methods that override the default page navigation behavior in WebViews. The default and safest behavior on Android is to let the default web browser open any link that the user clicks inside the WebView. However, this can be modified by configuring a WebViewClient with custom URL handling logic.

The following interception callback methods are relevant:

• shouldOverrideUrlLoading): allows the application to either abort loading WebViews with suspicious content by returning true or allow the WebView to load the URL by returning false. Note that this method is not called for POST requests, XmlHttpRequests, iFrames, "src" attributes in HTML, or <script> tags.
• shouldInterceptRequest): allows the application to return custom data from resource requests. This callback is invoked for various URL schemes (e.g., http(s):, data:, file:), but not for javascript: or blob: URLs, or for assets accessed via file:///android_asset/ or file:///android_res/.

If these methods are implemented without proper URL validation, the app may load content from untrusted sources or navigate users to malicious websites.

See MASTG-KNOW-0018 for more information on URL loading in WebViews.

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 a list of locations where WebViewClient URL loading handlers are used, including:

• Classes extending WebViewClient with shouldOverrideUrlLoading or shouldInterceptRequest implementations.
• Calls to setWebViewClient on WebView instances.

Evaluation

The test case fails if a WebViewClient URL interception method is implemented without properly restricting navigation to trusted content.

Further Validation Required:

Inspect each reported code location using MASTG-TECH-0023, looking for cases such as:

• No validation: the method does not check the URL against an allowlist or denylist before allowing navigation or returning resource data.
• Weak validation: the method performs validation that does not reliably prevent navigation to untrusted domains (for example, substring checks instead of validating the host).
• Missing client implementation: a WebViewClient is assigned to a WebView via setWebViewClient without overriding any interception method, leaving the default (unrestricted) navigation behavior in place for an app that intended to restrict it.

Note that using a WebViewClient is not inherently insecure. The test fails only when the URL handling logic does not properly restrict navigation to trusted content.

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