Deep Link / URL Scheme Hijack

← Improper Platform Usage

deeplink_url_scheme_hijack   MEDIUM

Description

Custom scheme is unvalidated and can be claimed/abused by another app.

How it works

The custom URL scheme is unverified, so any installed app can also register it, and its parameters are trusted as-is, so a crafted link can drive a password reset or an open redirect. Verified App Links or Universal Links should be used instead of a bare custom scheme.

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: Android: adb, drozer, jadx · iOS: xcrun simctl openurl, idb.
2. Locate the target. From the home index, open Deep Link / URL Scheme Hijack (deeplink_url_scheme_hijack). 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-0028, MASTG-TEST-0393, MASTG-TEST-0371 for the canonical procedure and remediation.

Tools (optional)

Android

• adb
• drozer
• jadx

iOS

• xcrun simctl openurl
• idb

Real-world references

Concrete public disclosures that match this vulnerability class:

• CVE-2026-23866 (WhatsApp iOS/Android: message payload dispatches an OS custom-scheme handler without validation, CWE-940)
• Android: verify App Links (autoVerify)
• Apple: supporting Universal Links