Handoff / NSUserActivity Injection

← Improper Platform Usage

handoff_useractivity_injection   MEDIUM

Description

The receiving app restores state from a Handoff NSUserActivity (userInfo / webpageURL) and TRUSTS it - navigating, mutating state, or acting on an account/resource - without validating the source device, activity type, or account binding, so a crafted continuation payload drives the app to a privileged/attacker-chosen state. Handoff data is treated as trusted merely because it arrived over Continuity. The secure path validates activityType, binds the activity to the authenticated account, and treats userInfo/webpageURL as untrusted input (iOS Handoff class).

How it works

The receiving app restores state from a Handoff NSUserActivity (userInfo or webpageURL) and trusts it merely because it arrived over Continuity. Without validating the source device, the activityType, or the account binding, a crafted continuation payload drives the app to operate on another account’s resource. The attacker-controlled webpageURL is parsed with a real URL parser and its query merged over userInfo. The secure path validates the parsed host against an associated-domain allowlist and the activityType against a known set, requires the activity to be bound to the current authenticated account, and treats userInfo and webpageURL as untrusted input.

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 Handoff / NSUserActivity Injection (handoff_useractivity_injection). 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 NSUserActivity payload

Real-world references

Concrete public disclosures that match this vulnerability class:

• Apple: NSUserActivity / Handoff and validating continuation payloads