Insecure WebView (JS Bridge RCE, file:// access)

← Improper Platform Usage

insecure_webview   HARD

Description

WebView exposes a JS bridge and enables file:// access for RCE-style abuse.

How it works

The WebView enables JavaScript, file:// access, and a native JS bridge (an addJavaScriptChannel named “Native”) with no origin allowlist, so a malicious or MITM’d page can call into app internals to read files and invoke native methods, an RCE-style abuse. This runs a real Android System WebView: the loaded page posts to the exposed Native channel and the native handler returns the app secret or an on-device file back to page JS.

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 Improper Platform Usage 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, r2frida, frida, objection · Android: jadx, apktool · iOS: ipsw, class-dump, Hopper, r2ghidra.
2. Locate the target. From the home index, open Insecure WebView (JS Bridge RCE, file:// access) (insecure_webview). 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. From a co-resident/attacker context (adb shell am start/drozer, or a crafted deep link / QR), send the untrusted input to the exported component or WebView and confirm the app performs the unsafe action (navigation, JS execution, file/URI access) with no validation.
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-0334, MASTG-TEST-0333, MASTG-TEST-0250 for the canonical procedure and remediation.

Tools (optional)

• mitmproxy
• r2frida
• frida
• objection

Android

• jadx
• apktool

iOS

• ipsw
• class-dump
• Hopper
• r2ghidra