Captcha and SSL Pinning Bypass in Mobile Apps

Hello, In this article, we will provide information on bypassing SSL Pinning Bypass and Captcha verifications, which are very often needed, and we will share a case.

Nowadays, security measures in mobile applications are becoming increasingly complex. Especially in applications that involve financial transactions, mechanisms such as Captcha Verification and SSL Pinning are widely used to make reverse engineering and traffic analysis difficult.

We recently conducted a comprehensive security testing and analysis process on an Android application whose name we had to keep secret. In this project, we managed to speed up the automated testing processes and analyze the application traffic by bypassing the Captcha verification of the application. At the same time, we performed SSL Pinning Bypass to be able to see all the traffic of the application through Burp Suite.

Captcha and SSL Pinning Bypass Process: A Real Project Experience

Dense Obfuscation Layers

The application in question used very serious obfuscation techniques both at the code level and at the network traffic level. Class and method names were changed with random letters, and the analysis process was made very difficult with reflection and dynamic loading techniques.

Obfuscation Layers – Technical Description

Code Level Obfuscation

• All class and method names were replaced with meaningless letter-number combinations such as A1, B3, C6.
• In addition to obfuscation using Proguard / Dexguard / R8 and similar tools, custom string encryption and dynamic class loading techniques were also used within the application.
• With Reflection, method calls were not made directly, but were executed by resolving method names at runtime.

Network Traffic Obfuscation

• API endpoints were not kept hardcoded directly within the application, but instead were stored in an encrypted form and decrypted when necessary.
• Request Headers and some critical parameters were being created in the native module (NDK layer) within the application, making it impossible to bypass by focusing only on the Java/Kotlin side.
• TLS Certificate Pinning is not just a simple pinning, but also a secondary layer of control is added using the runtime certificate validation hook.

Reflection & Dynamic Class Loading

• The application was calling critical functions with reflection and loading some classes from an external DEX file at runtime rather than directly in the APK, which prevented the full code from being visible to static analysis tools.
• In particular, the login, captcha and security check modules were called dynamically in this way.

Anti-Frida and Anti-Hooking Measures

• There were various checkpoints in the application for frida-server detection.
• In particular, monitoring activities on “TracerPID” and “/proc/net/tcp” were prepared to detect debugging or hooking attempts.

Such intense obfuscation and multi-layered security measures required much more advanced reverse engineering and anti-tamper bypass techniques than a typical mobile security testing process. In this project, these protection layers were successfully analyzed and neutralized with Frida, JADX, Objection, Burp Suite and our specially developed hook scripts.

APKM Format and Split APK Structure

The app was not in a standard APK format. Since it was provided in APKM (App Bundle) format, we had to deal with the steps of breaking down and assembling the app bundle before we could start the analysis process. This is a critical detail that many security researchers miss and that bogs down the process.

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Applied Solutions for Captcha Bypass & SSL Pinning

Captcha Bypass with Frida

The classes and methods used for captcha verification were dynamically hooked to Frida. In this way, the captcha requirement within the application was disabled and the testing processes were significantly accelerated. At the same time, direct access to login and other functions was provided without wasting time with the captcha screen in manual tests.

SSL Pinning Bypass

The application had tightened the certificate validation on the server side. For this reason, SSL Pinning was disabled using the classic “CertificatePinner” hook with Frida. Thus, all traffic can be easily monitored via Burp Suite.

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Why are these types of bypass operations important?

This type of analysis is valuable not only for security research, but also for commercial purposes such as developing automation processes, competitive analysis, and app debugging. Additionally, corporate companies that want to see how secure their applications are can test their own applications in this way to see potential vulnerabilities.

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Do You Need a Similar Project?

If you also want your mobile application to:

• If you want to test reverse engineering resistance,
• Analyze security controls,
• Monitor and analyze API traffic,
• Bypass protections such as Captcha and SSL Pinning, we, as the ReverseEngineer.net team, can provide you with professional support.

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