WebView URL-Loading Policy Confusion

← Native / WebView Bridge (JS <-> Native)

webview_url_loading_policy_confusion   HARD

Description

The WebView’s URL-policy handler (shouldOverrideUrlLoading / decidePolicyForNavigationAction) makes a trust decision on a raw, un-canonicalized URL, so scheme/host confusion (javascript:, file:, content:, a custom scheme, a redirect, or a malformed URL) slips past the allow/deny logic and loads privileged content. The bug is the policy IMPLEMENTATION, not merely calling loadUrl (Android/iOS URL-loading-handler MASTG-TEST-0332 class).

How it works

The WebView navigation-policy handler (shouldOverrideUrlLoading / decidePolicyForNavigationAction) makes its allow/deny trust decision on a raw, un-canonicalized URL. A naive substring check against the intended host lets scheme/host confusion slip through: javascript: (script), file:// (local file read), content:// (privileged provider), a look-alike subdomain (app.example.evil.com), or the genuine host smuggled into a query (evil.example/?next=app.example). The bug is the policy implementation, not loadUrl (MASTG-TEST-0332 class). This applies the naive policy in a real WebView navigation delegate and loads the crafted URL (the in-memory panel is the offline contrast). The secure path canonicalizes and parses the URL, then allowlists scheme (https only) and the exact host, rejecting the crafted URLs while allowing the genuine one.

How to exercise it. DVMA is the harness - open this module from the home index and tap the demo action. The screen ships the malicious input and simulates the attacker (e.g. the companion app, crafted intent, or scanned payload) in-process, and the evidence panel prints the proof. The Tools (optional) and Attack inputs below are only needed to reproduce the exploit end-to-end on a real device.

Exploit steps

1. Set up. Build DVMA with a flavor that enables the Native / WebView Bridge (JS <-> Native) category (e.g. --dart-define-from-file=config/flavors/dev.json) and run on an emulator/simulator you control. The demo needs no external tooling; for the optional on-device reproduction the relevant tools are: mitmproxy, frida, objection · Android: jadx · iOS: ipsw, Hopper.
2. Locate the target. From the home index, open WebView URL-Loading Policy Confusion (webview_url_loading_policy_confusion). The How it works section above describes this module’s specific weakness; the screen states the intended-secure behavior and exposes the vulnerable action.
3. Exploit. Reach the JS<->native bridge (or the framework/plugin API) from untrusted web content / a cross-origin iframe / a malicious provider, and confirm the privileged native call fires with no main-frame/origin, callback-id, or permission gate in between.
4. Observe the evidence. Trigger the vulnerable action and read the evidence panel - it prints the concrete proof (leaked value, accepted replay, executed payload, or unauthorized result).
5. Contrast with the secure path. Run the module’s secure/hardened action (where provided) and confirm the same attack is rejected - this is what a correct implementation should do.
6. Map it back. Cross-reference the MASTG v2 test(s) MASTG-TEST-0332, MASTG-TEST-0398 for the canonical procedure and remediation.

Tools (optional)

• mitmproxy
• frida
• objection

Android

• jadx

iOS

• ipsw
• Hopper

Attack inputs

Payloads/artifacts you author for the on-device attack. The demo already ships and simulates these in-process (e.g. the malicious companion app / crafted intent is emulated inside the screen), so you only need to craft them to reproduce the exploit on a real device:

• crafted navigation URL

Real-world references

Concrete public disclosures that match this vulnerability class:

• OWASP MASTG-TEST-0332: attacker-controlled URI in WebViews