Custom URL Scheme Authorization (arbitrary URL load)

← Improper Platform Usage

custom_url_scheme_authorization   MEDIUM

CategoryImproper Platform Usage
OWASP Mobile (2024)M4
MASVSMASVS-PLATFORM-3MASVS-CODE-4
MASWEMASWE-0029
MASTG (v2 tests)iOSMASTG-TEST-0371MASTG-TEST-0370AndroidNone published
MASTG demosiOSMASTG-DEMO-0134MASTG-DEMO-0135AndroidNone published
CWECWE-939CWE-862CWE-601
PlatformAndroidiOS

Description

A custom URL-scheme handler loads a caller-supplied URL without checking the caller or an allowlist, so any co-resident app can make DVMA display an attacker site (Rakuten CVE-2024-41918 / @cosme CVE-2024-45203 / Skylark CVE-2024-54014 / Groww CVE-2026-12065 class).

How it works

The app registers a custom URL scheme (dvma://open?url=…) whose handler loads the caller-supplied “url” parameter without checking the caller or an allowlist. Any co-resident app can fire the scheme and make DVMA render an attacker-controlled site inside its trusted chrome (Rakuten CVE-2024-41918 / @cosme CVE-2024-45203 / Skylark CVE-2024-54014 / Groww CVE-2026-12065 class). On Android the caller-supplied URL is loaded into a real in-app WebView inside DVMA’s trusted chrome. The secure path only displays https URLs on a trusted-host allowlist and refuses everything else.

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 Custom URL Scheme Authorization (arbitrary URL load) (custom_url_scheme_authorization). 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-0371, MASTG-TEST-0370 for the canonical procedure and remediation.

Tools (optional)

Android

iOS

Real-world references

Concrete public disclosures that match this vulnerability class: