From Encrypted Mobile Traffic to Payment Manipulation
How KomodoSec’s AigentX Penetration Tester reverse engineered client-side encryption, turned the bypass into reusable Burp tooling, and used that access to validate a real business-logic flaw in a production mobile application.
Client-side secrecy failed. Server-side trust became the real vulnerability.
THE CHALLENGE
A mobile app with TLS, certificate pinning, and a second encryption layer.
AigentX was used during an authorized assessment of an Android self-service application that enabled users to purchase online services. The client implemented several defensive layers: HTTPS, certificate pinning, and an additional application-level encryption envelope around API parameters.
Those controls made the traffic harder to inspect and manipulate, but they did not change the core security requirement. The backend still had to treat every value coming from the mobile client as attacker-controlled input.
THE OUTCOME
STEP 1. UNDERSTAND THE ENCRYPTION SCHEME
The “double encryption” was recoverable from the application itself
Static analysis showed that API parameters were wrapped in AES-256-CBC before being sent over HTTPS. The AES key was derived from hardcoded client-side material plus a per-install token. The IV derivation material was also hardcoded, producing a static IV for traffic using that scheme.
Critically, the per-install token needed for key derivation was sent in plaintext alongside the encrypted parameter. That meant the information required to reproduce the encryption process was available to anyone who could analyze the APK and observe a request.
Once the derivation logic and required value were known, the encryption layer could be reproduced.
STEP 2. TURN THE BYPASS INTO TOOLING
From a one-off decryptor to transparent Burp testing
The recovered scheme was first operationalized as a standalone Python helper capable of decrypting captured request data and re-encrypting modified plaintext in the format expected by the backend.
The workflow was then taken further with a custom Burp Suite extension. Instead of manually copying ciphertext out of Burp, decrypting it in a separate tool, editing it, and encrypting it again, the extension automated the process for common testing workflows.
OPERATIONALIZED TESTING FLOW
The supplied extension specifically supported workflows such as Repeater, Intruder, and Scanner, allowing plaintext parameters to be tested while preserving the ciphertext format expected on the wire.
The encryption bypass was not treated as the finish line. It became an enabling capability. Once the traffic could be manipulated reliably and repeatedly, AigentX could test the application’s server-side business logic as if the extra client-side encryption were not there.
STEP 3. TEST WHAT THE SERVER ACTUALLY TRUSTS
The payment amount was controlled by the client, and the backend accepted the change
With encrypted traffic now editable, AigentX inspected a payment flow that used a saved payment card to purchase an online service. The decrypted request contained a client-supplied amount parameter.
AigentX reduced that amount before the request was re-encrypted and forwarded to the backend. The server accepted the modified value without apparent server-side validation, completed the transaction, and returned a successful transaction response reflecting the reduced amount. The application also displayed confirmation to the user.
HIGH-RISK BUSINESS IMPACT
THE ATTACK CHAIN
A defense-in-depth control became a gateway to deeper testing
What began as a client-side protection problem became a business-logic problem. Once the encryption mechanism was understood and reproduced, AigentX could remove the friction created by the protection layer and continue testing the system underneath it.
MAIN 7-STEP ATTACK CHAIN
A SECOND DISCOVERY
The production app also contained a hidden developer interface
Static analysis also revealed a hidden developer feature accessible through the application’s About screen after repeated taps on the version text. The interface exposed developer-oriented functionality.
This mattered for a simple reason. Hidden is not the same as protected. Developer and maintenance features shipped in production can expose logs, alternate environments, diagnostic controls, or other functionality that was never intended for ordinary users.
THREE FINDINGS, ONE SECURITY LESSON
The client cannot be the security boundary
The assessment demonstrates why mobile protections should be treated as defense in depth rather than authorization or integrity controls. Certificate pinning and application-layer encryption can increase the complexity of successful traffic interception, but a determined attacker controls the client device and can reverse engineer the application.
Once that happens, the backend must remain secure even if every client-side protection has been removed. Transaction prices, authorization decisions, rate limits, and other security-sensitive state must be validated independently on the server.
WHAT AIGENTX DID DIFFERENTLY
It did not stop when the encryption broke
The most important part of this case was progression. Recovering the encryption mechanism produced a new testing capability. The standalone Python helper made the capability repeatable. The Burp extension made it operational at testing speed. That tooling then unlocked deeper business-logic testing, which produced the highest-risk finding in the story.
AGENTIC TESTING IN PRACTICE
DEFENDER TAKEAWAY
Encrypting attacker-controlled input does not make it trustworthy
The application’s additional encryption layer raised the technical bar, but the backend still received data ultimately controlled by the mobile client. The assessment showed that the encryption could be reproduced because the necessary derivation material lived in the client and the per-install value required for key derivation traveled with the request.
The recommended design principle is straightforward. Assume client-side protections can be bypassed. Enforce transaction integrity, authorization, session security, rate limiting, and input validation on the server. If application-layer encryption is retained, avoid static IVs and client-embedded secrets, and use modern per-session key establishment rather than relying on secrets that must ship with the application.
CONCLUSION
From ciphertext to a real transaction flaw
AigentX began with traffic intentionally made difficult to inspect. It reverse engineered the client-side encryption, reproduced the scheme externally, converted the bypass into transparent Burp tooling, and then used that capability to reach the finding that mattered most. The backend accepted a manipulated payment amount.
The same assessment also showed that hidden developer functionality remained accessible in the production application. Together, the findings reinforce a fundamental security principle. Client-side controls can slow an attacker down, but they cannot replace server-side trust boundaries.
AigentX Mobile Penetration Testing
Go beyond “the application’s traffic is encrypted.” Test whether the backend is still secure after the protection layer is removed.
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