iOS UIActivity Sharing Analysis

A skill for security testers to analyze iOS applications for vulnerabilities in their UIActivity sharing implementation.

Overview

iOS apps can share data (text, URLs, images) through the system-wide share activity sheet. This skill helps you:

• Analyze sharing mechanisms - How the app sends data to other apps
• Audit receiving capabilities - What document types the app can accept
• Identify vulnerabilities - Missing validation, exposed activities, insecure data handling

Static Analysis

1. Examine UIActivityViewController Initialization

Search for how the app creates share sheets:

# Find UIActivityViewController references
rabin2 -zq <app_name>.app/<app_name> | grep -i activity

# Look for activityItems initialization
rabin2 -zq <app_name>.app/<app_name> | grep -i activityItems

# Check for excludedActivityTypes
rabin2 -zq <app_name>.app/<app_name> | grep -i excluded

What to look for:

• What data is being passed to

  initWithActivityItems:applicationActivities:

• Whether

  excludedActivityTypes

  is properly configured
• If custom activities are added (potential attack surface)
• Sensitive data being shared without proper sanitization

2. Audit Info.plist Document Type Declarations

Check the app's

Info.plist

# Extract and search Info.plist
plutil -p <app_name>.app/Info.plist | grep -A 20 -i "document\|uti\|type"

Key declarations to examine:

UTExportedTypeDeclarations

UTImportedTypeDeclarations

CFBundleDocumentTypes

Example Info.plist structure:

<key>UTExportedTypeDeclarations</key>
<array>
  <dict>
    <key>UTTypeIdentifier</key>
    <string>com.example.app.document</string>
    <key>UTTypeDescription</key>
    <string>Example Document</string>
  </dict>
</array>

<key>CFBundleDocumentTypes</key>
<array>
  <dict>
    <key>CFBundleTypeName</key>
    <string>Example Document</string>
    <key>CFBundleTypeRole</key>
    <string>Editor</string>
    <key>LSItemContentTypes</key>
    <array>
      <string>com.example.app.document</string>
    </array>
  </dict>
</array>

Dynamic Testing

Testing Data Sending

1. Hook UIActivityViewController initialization:

   // Frida hook example
   Interceptor.attach(ObjC.classes.UIActivityViewController.init,
     {
       onEnter: function(args) {
         console.log("UIActivityViewController initialized");
         console.log("Activity items:", args[2]);
       }
     }
   );
   

2. Capture shared data:

   • Trigger the share action in the app
   • Observe what data is passed to the share sheet
   • Check if sensitive information is exposed

3. Test excluded activities:

   • Verify that

     excludedActivityTypes

     is working
   • Attempt to share via excluded methods
   • Check if exclusions can be bypassed

Testing Data Receiving

1. Share files to the app:

   • Use AirDrop, email, or other apps to share files
   • Trigger the "Open with..." dialogue
   • Observe which file types the app accepts

2. Hook URL handling:

   // Hook application:openURL:options:
   Interceptor.attach(ObjC.selector('application:openURL:options:'),
     {
       onEnter: function(args) {
         console.log("URL opened:", args[2].toString());
       }
     }
   );
   

3. Fuzz with malformed files:

   • Create files with valid extensions but invalid content
   • Test with oversized files
   • Try files with embedded scripts or payloads
   • Observe app behavior and error handling

Common Vulnerabilities

1. Insecure Data Sharing

• Sensitive data shared without encryption
• Personal information exposed in share sheet
• Authentication tokens passed in shared content

2. Missing Input Validation

• No validation of received document types
• Improper handling of malformed files
• Buffer overflows from large file inputs

3. Improper Activity Exclusions

• Sensitive activities not excluded (e.g., saving to cloud)
• Custom activities with insecure implementations
• No filtering of share destinations

4. Document Type Confusion

• Accepting dangerous file types (scripts, executables)
• No verification of file content vs. extension
• Improper handling of nested archives

Testing Checklist

• Identify all UIActivityViewController instantiations
• Review what data is being shared
• Check excludedActivityTypes configuration
• Audit Info.plist for document type declarations
• Test sharing sensitive data
• Test receiving various file types
• Fuzz with malformed files
• Hook and monitor data flow
• Verify input validation on received data
• Check for custom activity implementations

Reporting Findings

When documenting vulnerabilities:

1. Describe the issue - What vulnerability was found
2. Show the evidence - Code snippets, plist entries, or dynamic test results
3. Explain the impact - What an attacker could do
4. Provide remediation - How to fix the issue

References

• Apple Inter-App Communication Guide
• UIActivity.ActivityType Documentation
• Mobile Security Testing Guide - iOS Platform Interaction
• StackOverflow: UTImportedTypeDeclarations and UTExportedTypeDeclarations