How to Block Method Swizzling

Last updated December 3, 2023 by Appdome

Learn to Block Method Swizzling in iOS apps, in mobile CI/CD with a Data-Driven DevSecOps™ build system.

What is Method Swizzling?

Method Swizzling means changing the functionality of an existing method by replacing it with another, user-created method. In iOS, this technique is one of the Objective-C language features. Using the Objective-C API a developer can, for example, replace the method in charge of the clicks in the Button class with a function that counts how many times the user clicked on each button. Many SDKs use method swizzling to modify the behavior of applications during runtime (e.g: a crash handler), thus saving the app’s developers the need to write sections of code that are repeated in multiple places (boilerplate code).

Why Block Method Swizzling?

While method swizzling was designed for legitimate use (mostly by developers), “black hat” hackers also use method swizzling to alter the behavior of other apps, in the process of creating and distributing malware and (jailbroken) iPhone tweaks. For instance, a malicious attacker can swizzle the method responsible for the Internet connections and change the destination of these connections, or even steal user data. Users can use tweaks that exploit this Swizzling mechanism to bypass the application security features, inspect or modify the business logic of the app, or cheat in mobile games and have an unfair advantage over other users.

Method swizzling can be performed at both the system and the application level. As a result, even if a specific app class was not tampered with, the class may use a maliciously modified system class. Therefore, each class used by the application, either directly or indirectly, needs protection.

Prerequisites for Using Anti-Swizzling:

To use Appdome’s mobile app security build system to Block Method Swizzling , you’ll need:

Block Method Swizzling on iOS apps using Appdome

On Appdome, follow these 3 simple steps to create self-defending iOS Apps that Block Method Swizzling without an SDK or gateway:

  1. Upload the Mobile App to Appdome.

    1. Upload an app to Appdome’s Mobile App Security Build System

    2. Upload Method: Appdome Console or DEV-API
    3. iOS Formats: .ipa
    4. Anti-Swizzling Compatible With: Obj-C, Java, Swift, Flutter, React Native, Unity, Xamarin, Cordova and more
  2. Build the feature: Anti-Swizzling.

    1. Building Anti-Swizzling by using Appdome’s DEV-API:

      1. Create and name the Fusion Set (security template) that will contain the Anti-Swizzling feature as shown below:
      2. fusion set that contains Anti-Swizzling

        Figure 1: Fusion Set that will contain the Anti-Swizzling feature
        Note: Naming the Fusion Set to correspond to the protection(s) selected is for illustration purposes only (not required).

      3. Follow the steps in Sections 2.2.1-2.2.2 of this article, Building the Anti-Swizzling feature via Appdome Console, to add the Anti-Swizzling feature to this Fusion Set.

      4. Open the Fusion Set Detail Summary by clicking the “...” symbol on the far-right corner of the Fusion Set, as shown in Figure 1 above, and get the Fusion Set ID from the Fusion Set Detail Summary (as shown below): fusion Set Detail Summary image

        Figure 2: Fusion Set Detail Summary
        Note: Annotating the Fusion Set to identify the protection(s) selected is optional only (not mandatory).

      5. Follow the instructions below to use the Fusion Set ID inside any standard mobile DevOps or CI/CD toolkit like Bitrise, App Center, Jenkins, Travis, Team City, Circle CI or other system:
        1. Build an API for the app – for instructions, see the tasks under Appdome API Reference Guide
        2. Look for sample APIs in Appdome’s GitHub Repository
    2. Building the Anti-Swizzling feature via Appdome Console

      To build the Anti-Swizzling protection by using Appdome Console, follow the instructions below.

      1. Where: Inside the Appdome Console, go to Build > Anti Fraud Tab > Mobile Malware Prevention section.
      2. When you select the Anti-Swizzling you'll notice that your Fusion Set you created in step 2.1.1 now bears the icon of the protection category that contains Anti-Swizzling

        Fusion Set applied Anti-Swizzling

        Figure 4: Fusion Set that displays the newly added Anti-Swizzling protection

      3. Select the Threat-Event™ in-app mobile Threat Defense and Intelligence policy for Anti-Swizzling:
        1. Threat-Events™ OFF > In-App Defense

          If the Threat-Events™ setting is cleared (not selected). Appdome will detect and defend the user and app by enforcing Block Method Swizzling.

        2. Threat-Events™ ON > In-App Detection

          When this setting is used, Appdome detects method swizzling and passes Appdome’s Threat-Event™ attack intelligence to the app’s business logic for processing, enforcement, and user notification. For more information on consuming and using Appdome Threat-Events™ in the app, see section Using Threat-Events™ for Anti-Swizzling Intelligence and Control in Mobile Apps.

        3. Threat-Events™ ON > In-App Defense

          When this setting is used, Appdome detects and defends against Method Swizzling (same as Appdome Enforce) and passes Appdome’s Threat-Event™ attack intelligence the app’s business logic for processing. For more information on consuming and using Appdome Threat-Events™ in the app, see section Using Threat-Events™ for Anti-Swizzling Intelligence and Control in Mobile Apps.

      4. Click Build My App at the bottom of the Build Workflow (shown in Figure 3).
    Congratulations!  The Anti-Swizzling protection is now added to the mobile app

Using Threat-Events™ for Method Swizzling Intelligence and Control in iOS Apps

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

The specifications and options for Threat-Events™ for Method Swizzling are:

Threat-Event™ Elements Block Method Swizzling Method Detail
Appdome Feature Name Anti-Swizzling
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
Visible in ThreatScope™
Developer Parameters for Blocking Method Swizzling Threat-Event™
Threat-Event NAME MethodSwizzlingDetected
Threat-Event DATA reasonData
Threat-Event CODE reasonCode
Threat-Event REF 6801
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
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.
carrierPlmn PLMN of the device
deviceID Current device ID
reasonCode Reason code of the occured event
buildDate Appdome fusion date of the current application
devicePlatform OS name of the current device
carrierName Carrier 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

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 Method Swizzling is detected.

The following is a code sample for native iOS apps, which uses all values in the specification above for Anti-Swizzling:


Using Appdome, there are no development or coding prerequisites to build secured iOS Apps by using Anti-Swizzling. 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 Anti-Swizzling

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:

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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