“The Balance Increased?”
Hooking-Based Balance and Credit Limit Manipulation: The Most Dangerous Attack Threatening Financial Apps
“Payment was approved even though the account balance was insufficient.”
One day, a fintech company (Company A) that provided both digital payment and microloan services began receiving unusual inquiries through its customer support center.
At first, the company assumed these were simple mistakes or user misunderstandings. However, the reports became increasingly specific.
• ✔ A payment was approved even though the balance was zero.
• ✔ The loan limit suddenly increased.
• ✔ Everything appeared normal within the app.
The operations team immediately reviewed server logs and payment records.
However, the results were unexpected.
• ✔ Server logs were completely normal.
• ✔ Payment approval and rejection logic functioned correctly.
• ✔ No signs of external intrusion were found.
“This is strange... The servers appear normal, so why is this happening?”
The Real Problem – The Server Wasn't Being Deceived, the App Was
As the investigation continued, the security team discovered a common pattern.
Most of the affected accounts were accessing the service through specific Android environments.
A deeper analysis revealed that attackers had not breached the server.
Instead, they were manipulating the application running on the user's smartphone.
How the Attack Actually Worked
• ✔ Using hooking tools to access application memory during runtime
• ✔ Forcing changes to the return values of balance and credit limit functions
○ return false → return true
• ✔ Displaying “Sufficient Balance” on the application screen
• ✔ Sending payment and transfer requests to the server as if they were legitimate users
In other words:
The server was never compromised, but the application had already been manipulated.
The server received what appeared to be legitimate requests, users saw successful approvals, and financial incidents occurred in the gap between them.
Why Is This Attack So Dangerous for Financial Apps?
The most frightening aspect of hooking-based attacks is that everything appears normal on the surface.
• ✔ Users see approval screens and assume everything is legitimate.
• ✔ Server logs show no abnormalities.
• ✔ Small fraudulent transactions can be repeated without attracting attention.
• ✔ Losses accumulate while the root cause remains difficult to identify.
For financial and fintech applications, this is not merely a software bug—it directly impacts trust.
• Customers begin to think, “This app cannot be trusted.”
• Financial institutions become exposed to audit and regulatory risks.
• Trust, once lost, is extremely difficult to regain.
At that moment, the operations team realized an important fact:
“Server security alone cannot protect a financial application.”
A New Security Strategy – Protect the Application Itself
Company A completely changed its approach.
“If attacks originate from the application, then the application itself must be protected.”
This led to the implementation of a mobile security framework centered around LIAPP, LIKEY, and LISS.
LIAPP – Creating a Trusted Application Runtime Environment
The core of the solution was LIAPP.
How LIAPP Was Applied
• ✔ Runtime integrity verification
→ Real-time detection of code and memory tampering
• ✔ Hooking and debugging detection
→ Immediate application termination upon detection
• ✔ Memory manipulation prevention
→ Preventing unauthorized modification of balance and credit limit functions
• ✔ Restricting access from untrusted environments
→ Blocking rooted devices, emulators, and hacking tools
• ✔ Detection of automated input and macro-based behavior
• ✔ Neutralization of fake-screen overlay attacks
In particular, additional integrity checks were performed immediately before payment and transfer transactions, protecting the entire transaction flow.
LIKEY – Extending Protection to Authentication and User Input
The operations team decided to go one step further.
“What if attackers steal login credentials first?”
To address this concern, LIKEY (Mobile Secure Keypad) was deployed alongside LIAPP.
The Role of LIKEY
• ✔ Encryption of user keystrokes
• ✔ Protection against keylogger-based credential theft
• ✔ Security for login, password, and payment authentication processes
As a result, the attack chain leading from credential theft to hooking attacks could be blocked entirely.
LISS – Preventing Information Exposure Through the Screen
Finally, LISS was added to strengthen protection.
Benefits of Implementing LISS
• ✔ Blocking screenshots and screen recordings
• ✔ Blocking unauthorized overlay applications
This eliminated the possibility of balance information, credit limits, and payment screens being exposed to external parties.
Results – “This App Can No Longer Be Hooked”
The results after implementation were clear.
• ✔ Complete prevention of balance and credit limit manipulation attempts
• ✔ Zero payment-related incident reports
• ✔ Successful completion of internal security audits
• ✔ Restoration of customer trust
Security researchers monitoring underground communities even found comments such as:
“You can't hook this app anymore.”
Only then did the operations team finally breathe a sigh of relief.
Key Lessons for Financial Application Security
The lesson Company A learned was straightforward:
Financial application security is not simply about protecting servers—it is about protecting trust.
• Server security alone is not enough.
• Network protection alone is not enough.
• The application in the user's hands must be secure.
The Minimum Security Framework for Financial and Fintech Applications
Today, the following security measures are no longer optional for financial applications—they are fundamental requirements.
• LIAPP → Application integrity protection, anti-hooking, anti-tampering, and anti-repackaging
• LIKEY → Protection of authentication and sensitive user input
• LISS → Prevention of screen capture and information leakage
These are not merely individual security features. Together, they form a comprehensive security system required to operate modern financial services safely.
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