iOS UIActivity Sharing - HackTricks

# iOS UIActivity Sharing

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# UIActivity Sharing Simplified

From iOS 6 onwards, third-party applications have been enabled to share data such as text, URLs, or images using mechanisms like AirDrop, as outlined in Apple's Inter-App Communication guide. This feature manifests through a system-wide share activity sheet that surfaces upon interacting with the "Share" button.

A comprehensive enumeration of all the built-in sharing options is available at UIActivity.ActivityType. Developers may opt to exclude specific sharing options if they deem them unsuitable for their application.

## How to Share Data

Attention should be directed towards:

- The nature of the data being shared.
- The inclusion of custom activities.
- The exclusion of certain activity types.

Sharing is facilitated through the instantiation of a `UIActivityViewController`, to which the items intended for sharing are passed. This is achieved by calling:

    $ rabin2 -zq Telegram\ X.app/Telegram\ X | grep -i activityItems
    0x1000df034 45 44 initWithActivityItems:applicationActivities:

Developers should scrutinize the `UIActivityViewController` for the activities and custom activities it's initialized with, as well as any specified `excludedActivityTypes`.

## How to Receive Data

The following aspects are crucial when receiving data:

- The declaration of custom document types.
- The specification of document types the app can open.
- The verification of the integrity of the received data.

Without access to the source code, one can still inspect the `Info.plist` for keys like `UTExportedTypeDeclarations`, `UTImportedTypeDeclarations`, and `CFBundleDocumentTypes` to understand the types of documents an app can handle and declare.

A succinct guide on these keys is available on Stackoverflow, highlighting the importance of defining and importing UTIs for system-wide recognition and associating document types with your app for integration in the "Open With" dialogue.

## Dynamic Testing Approach

To test sending activities, one could:

- Hook into the `init(activityItems:applicationActivities:)` method to capture the items and activities being shared.
- Identify excluded activities by intercepting the `excludedActivityTypes` property.

For receiving items, it involves:

- Sharing a file with the app from another source (e.g., AirDrop, email) that prompts the "Open with..." dialogue.
- Hooking `application:openURL:options:` among other methods identified during static analysis to observe the app's response.
- Employing malformed files or fuzzing techniques to evaluate the app's robustness.

## References

- https://mobile-security.gitbook.io/mobile-security-testing-guide/ios-testing-guide/0x06h-testing-platform-interaction

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