Use AI to Obfuscate Obj-C SelRef in iOS Apps Fast to Prevent Reverse Engineering

Last updated February 9, 2025 by Appdome

This Knowledge Base article describes how to use Appdome’s AI/ML in your CI/CD pipeline to continuously deliver plugins that Protect Obj-C SelRef in iOS apps.

What Are SelRefs?

In Objective-C applications, selectors (SelRefs) are used to reference methods dynamically at runtime. These selectors are stored in a global table within the Mach-O file and can be accessed or modified externally, exposing them to tampering and manipulation. Attackers can target this structure to modify or redirect function calls, potentially hijacking the app’s behavior. For instance, by modifying selectors, hackers can change the intended method or function execution, compromising app security and leading to potential vulnerabilities such as code injection or unauthorized execution of malicious code. Protecting SelRefs is essential to prevent unauthorized method manipulation, securing the app’s internal logic, and supporting regulatory requirements like PCI-DSS.

How Appdome protects Obj-C SelRefs to Prevent iOS Reversing?

Appdome’s dynamic Obj-C SelRef Protection plugin for iOS defends against tampering with the global selector table in Objective-C applications. The plugin continuously monitors the selector table for unauthorized changes, preventing manipulation of method references. If an attempt is made to modify or replace a method’s selector, the app is immediately shut down to prevent further damage. This protection is essential for stopping reverse-engineering efforts, ensuring accurate method references, and blocking attackers from hijacking method calls for malicious actions.

Prerequisites for Using Appdome's Obj-C SelRef Protection Plugins:

To use Appdome’s mobile app security build system to Protect Obj-C SelRef , you’ll need:

How to Implement Protect Obj-C SelRef in iOS Apps Using Appdome

On Appdome, follow these 3 simple steps to create self-defending iOS Apps that Protect Obj-C SelRef without an SDK or gateway:

  1. Designate the Mobile App to be protected.

    1. Upload an app via the Appdome Mobile Defense platform GUI or via Appdome’s DEV-API or CI/CD Plugins.

    2. iOS Formats: .ipa
    3. Obj-C SelRef Protection is compatible with: Obj-C, Java, Swift, Flutter, React Native, Unity, Xamarin, Cordova and other iOS apps.
  2. Select the defense: Obj-C SelRef Protection.

      1. Create and name the Fusion Set (security template) that will contain the Obj-C SelRef Protection feature as shown below:
        fusion set that contains Obj-C SelRef Protection

        Figure 1: Fusion Set that will contain the Obj-C SelRef Protection feature

      2. Follow the steps in Sections 2.2-2.2.2 of this article to add the Obj-C SelRef Protection feature to your Fusion Set via the Appdome Console.

      3. When you select the Obj-C SelRef Protection you'll notice that the Fusion Set you created in step 2.1 now bears the icon of the protection category that contains Obj-C SelRef Protection.

        Fusion Set applied Obj-C SelRef Protection

        Figure 2: Fusion Set that displays the newly added Obj-C SelRef Protection protection
        Note: Annotating the Fusion Set to identify the protection(s) selected is optional only (not mandatory).

      4. Open the Fusion Set Detail Summary by clicking the “...” symbol on the far-right corner of the Fusion Set. Copy the Fusion Set ID from the Fusion Set Detail Summary (as shown below): fusion Set Detail Summary image

        Figure 3: Fusion Set Detail Summary

      5. Follow the instructions below to use the Fusion Set ID inside any standard mobile DevOps or CI/CD toolkit like Bitrise, Jenkins, Travis, Team City, Circle CI or other system:
        1. Refer to the Appdome API Reference Guide for API building instructions.
        2. Look for sample APIs in Appdome’s GitHub Repository.
    1. Add the Obj-C SelRef Protection feature to your security template.

      1. Navigate to Build > Security tab > ONEShield™ section in the Appdome Console.
      2. Toggle On > Obj-C SelRef Protection.
        Obj-C SelRef Protection option

        Figure 4: Selecting Protect Obj-C SelRef

    2. Initiate the build command either by clicking Build My App at the bottom of the Build Workflow (shown in Figure 4) or via your CI/CD as described in Section 2.1.4.
    Congratulations!  The Obj-C SelRef Protection protection is now added to the mobile app
  3. Certify the Obj-C SelRef Protection feature in iOS Apps

    After building Obj-C SelRef Protection, Appdome generates a Certified Secure™ certificate to guarantee that the Obj-C SelRef Protection protection has been added and is protecting the app. To verify that the Obj-C SelRef Protection protection has been added to the mobile app, locate the protection in the Certified Secure™ certificate as shown below: Obj-C SelRef Protection shown in Certificate secure

    Figure 5: Certified Secure™ certificate

    Each Certified Secure™ certificate provides DevOps and DevSecOps organizations the entire workflow summary, audit trail of each build, and proof of protection that Obj-C SelRef Protection has been added to each iOS app. Certified Secure provides instant and in-line DevSecOps compliance certification that Obj-C SelRef Protection and other mobile app security features are in each build of the mobile app.

Using Threat-Events™ for Obj-C SelRef Intelligence and Control in iOS Apps

Appdome Threat-Events™ provides consumable in-app mobile app attack intelligence and defense control when Obj-C SelRef is detected. To consume and use Threat-Events™ for Obj-C SelRef in iOS Apps, use AddObserverForName in Notification Center, and the code samples for Threat-Events™ for Obj-C SelRef shown below.

The specifications and options for Threat-Events™ for Obj-C SelRef are:

Threat-Event™ Elements Protect Obj-C SelRef Method Detail
Appdome Feature Name Obj-C SelRef Protection
Threat-Event Mode
OFF, IN-APP DEFENSE Appdome detects, defends and notifies user (standard OS dialog) using customizable messaging.
ON, IN-APP DETECTION Appdome detects the attack or threat and passes the event in a standard format to the app for processing (app chooses how and when to enforce).
ON, IN-APP DEFENSE Uses Appdome Enforce mode for any attack or threat and passes the event in a standard format to the app for processing (gather intel on attacks and threats without losing any protection).
Certified Secure™ Threat Event Check x
Visible in ThreatScope™ x
Developer Parameters for Protecting Obj-C SelRef Threat-Event™
Threat-Event NAME
Threat-Event DATA reasonData
Threat-Event CODE reasonCode
Threat-Event REF
Threat-Event SCORE
currentThreatEventScore Current Threat-Event score
threatEventsScore Total Threat-events score
Threat-Event Context Keys
message Message displayed for the user on event
failSafeEnforce Timed enforcement against the identified threat
externalID The external ID of the event which can be listened via Threat Events
osVersion OS version of the current device
deviceModel Current device model
deviceManufacturer The manufacturer of the current device
fusedAppToken The task ID of the Appdome fusion of the currently running app
kernelInfo Info about the kernel: system name, node name, release, version and machine.
deviceID Current device ID
reasonCode Reason code of the occurred event
buildDate Appdome fusion date of the current application
devicePlatform OS name of the current device
updatedOSVersion Is the OS version up to date
timeZone Time zone
deviceFaceDown Is the device face down
locationLong Location longitude conditioned by location permission
locationLat Location latitude conditioned by location permission
locationState Location state conditioned by location permission
wifiSsid Wifi SSID
wifiSsidPermissionStatus Wifi SSID permission status
threatCode The last six characters of the threat code specify the OS, allowing the Threat Resolution Center to address the attack on the affected device.

With Threat-Events™ enabled (turned ON), iOS developers can get detailed attack intelligence and granular defense control in iOS applications and create amazing user experiences for all mobile end users when Obj-C SelRef is detected.


The following is a code sample for native iOS apps, which uses all values in the specification above for Obj-C SelRef Protection:


Important! Replace all placeholder instances of <Context Key> with the specific name of your threat event context key across all language examples. This is crucial to ensure your code functions correctly with the intended event data. For example, The <Context Key> could be the message, externalID, OS Version, reason code, etc.



Using Appdome, there are no development or coding prerequisites to build secured Apps by using Obj-C SelRef Protection. There is no SDK and no library to code or implement in the app and no gateway to deploy in your network. All protections are built into each app and the resulting app is self-defending and self-protecting.

Releasing and Publishing Mobile Apps with Obj-C SelRef Protection

After successfully securing your app by using Appdome, there are several available options to complete your project, depending on your app lifecycle or workflow. These include:

Related Articles:

How to Prevent Code Tampering in Android Apps

How to Prevent Code Tampering in iOS Apps

How to Automatically Validate Android and iOS App Logic & File Structure in CI/CD

How to Obfuscate Security Features on Appdome

 

How Do I Learn More?

If you have any questions, please send them our way at support.appdome.com or via the chat window on the Appdome platform.

Thank you!

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