How to use DNS over TCP to Prevent MiTM Attacks in Android & iOS Apps

Last updated November 20, 2023 by Appdome

Learn to Prevent blocking the transfer of DNS over TCP in Mobile apps, in mobile CI/CD with a Data-Driven DevSecOps™ build system.

Why Permit DNS over TCP?

Usually, DNS resolution is performed over UDP. This protocol enables a fast, stateless query-response model and is used by DNS to achieve rapid resolution and lookups between hostnames and IP addresses.

Nevertheless, in some cases it is preferable to resolve DNS queries over TCP, for the following reasons:

  • Operationally, the UDP payload is limited in size (up to 512b), while TCP has no such restriction. This means that on a single DNS TCP query you can return more hosts to IP resolutions than over UDP. This capability is a clear advantage for sites that have global resolution based on location.
  • From a security standpoint, DNSSEC can only reliably be applied over TCP.

How does Appdome implement DNS Transfer over TCP?

Applying DNS transfer over TCP can be complicated. Moreover, if your infrastructure fails to support TCP, or blocks DNS over TCP at the network layer, this may lead to resolution failure, application-level timeouts, or both.

Appdome’s Permit DNS over TCP feature enables this operation for Android and iOS apps without coding.

Prerequisites to Using Permit DNS over TCP:

To use Appdome’s mobile app security build system to Prevent blocking the transfer of DNS over TCP , you’ll need:

Prevent blocking the transfer of DNS over TCP on Mobile apps using Appdome

On Appdome, follow these 3 simple steps to create self-defending Mobile Apps that Prevent blocking the transfer of DNS over TCP 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. Mobile App Formats: .ipa For iOS device or .apk or .aab
    4. Permit DNS over TCP Compatible With: Obj-C, C+, Java, JS, C#, C++, Swift, Kotlin, Flutter, React Native, Unity, Xamarin, and more
  2. Build the feature: Permit DNS over TCP.

    1. Building Permit DNS over TCP by using Appdome’s DEV-API:

      1. Create and name the Fusion Set (security template) that will contain the Permit DNS over TCP feature as shown below:
      2. fusion set that contains Permit DNS over TCP

        Figure 1: Fusion Set that will contain the Permit DNS over TCP 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 Permit DNS over TCP feature via Appdome Console, to add the Permit DNS over TCP 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, Cirlce 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 Permit DNS over TCP feature via Appdome Console

      To build the Permit DNS over TCP protection by using Appdome Console, follow the instructions below.

      1. Where: Inside the Appdome Console, go to Build > Security Tab > Secure Communication section
      2. How: Toggle (turn ON) Permit DNS over TCP, as shown below.
        If needed, Customize the Threat Notification to be displayed to the mobile end-user in a standard OS dialog notification when Appdome Prevents blocking the transfer of DNS over TCP. Permit DNS over TCP option

        Figure 3: Prevent blocking the transfer of DNS over TCP option
        Note: The App Compromise Notification contains an easy to follow default remediation path for the mobile app end user. You can customize this message as required to achieve brand specific support, workflow or other messaging.

      3. When you select the Permit DNS over TCP you'll notice that your Fusion Set you created in step 2.1.1 now bears the icon of the protection category that contains Permit DNS over TCP

        Fusion Set applied Permit DNS over TCP

        Figure 4: Fusion Set that displays the newly added Permit DNS over TCP protection

      4. Click Build My App at the bottom of the Build Workflow (shown in Figure 3).
    Congratulations!  The Permit DNS over TCP protection is now added to the mobile app
  3. Certify the Permit DNS over TCP feature in Mobile Apps.

    After building Permit DNS over TCP, Appdome generates a Certified Secure™ certificate to guarantee that the Permit DNS over TCP protection has been added and is protecting the app. To verify that the Permit DNS over TCP protection has been added to the mobile app, locate the protection in the Certified Secure™ certificate as shown below: Permit DNS over TCP 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 Permit DNS over TCP has been added to each Mobile app. Certified Secure provides instant and in-line DevSecOps compliance certification that Permit DNS over TCP and other mobile app security features are in each build of the mobile app

Using Appdome, there are no development or coding prerequisites to build secured Mobile Apps by using Permit DNS over TCP. 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 Permit DNS over TCP

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:

All apps protected by Appdome are fully compatible with any public app store, including Apple App Store, Google Play, Huawei App Gallery and more.

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

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