iOS Capability-Composition Chain

← Improper Platform Usage

ios_capability_composition_chain   HARD

Description

The vulnerability is the CHAIN, not any one API. A Universal Link resolves to an App Intent -> perform() reads its parameter as a security-scoped file reference -> resolves a persisted bookmark -> reads Contacts and exports them, with each hop inheriting trust from the last rather than re-authorizing the untrusted link. A crafted link therefore drives a full contacts export with no user authorization, even though matching a link, running an App Intent, resolving a bookmark, and reading Contacts are each individually legitimate. The secure path treats the link as untrusted, requires fresh user authorization at the App Intent for destructive/protected-data actions, and re-validates the bookmark scope before the sink (capability-composition / confused-deputy chain).

How it works

The vulnerability is the chain, not any one API. A Universal Link resolves to an App Intent whose perform() reads its parameter as a security-scoped file reference, resolves a persisted bookmark, and reads and exports Contacts, each hop inheriting trust from the last rather than re-authorizing the untrusted link (a confused deputy). A crafted link therefore drives a full contacts export with no user authorization, even though matching a link, running an App Intent, resolving a bookmark, and reading Contacts are each individually legitimate. This is an offline, deterministic simulation. The secure path treats the link as untrusted, requires fresh user authorization at the App Intent for the protected-data action, and re-validates the bookmark scope before the sink.

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 iOS simulator / a device you control. The demo needs no external tooling; for the optional on-device reproduction the relevant tools are: ipsw, Hopper, frida.
2. Locate the target. From the home index, open iOS Capability-Composition Chain (ios_capability_composition_chain). 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 an attacker context (a crafted custom-URL-scheme / Universal Link, a malicious document provider / share extension, or a Shortcut), send the untrusted input to the handler and confirm the app performs the unsafe action (navigation, file/URL access, privileged operation) 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.

Tools (optional)

• ipsw
• Hopper
• frida

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 universal-link URL

Real-world references

Concrete public disclosures that match this vulnerability class:

• Apple App Intents + associated domains: authorization must be re-checked per hop