How to bypass CVV code

Question

I want to understand the methods used to bypass CVV verification during online transactions. What vulnerabilities or techniques could allow this, and how do payment gateways implement security measures to prevent such exploits?

I’m curious about the technical processes involved in these systems and how attackers might target them.

Answer 1

In order to understand how attackers bypass CVV codes during online transaction, let's talk about how CVV works:

What is CVV?

The CVV code is a security feature on credit and debit cards to verify that the person making the transaction physically possesses the card.

Usage:

CVV is typically required during online transactions to prevent the misuse of stolen card numbers.

Verification:

The CVV code is not stored by merchants or payment processors per Payment Card Industry Data Security Standard (PCI DSS), ensuring it must be entered manually for each transaction.

Let's try to understand how we can bypass CVV:

Case 1: OTP Received Only If CVV is Correct

• In this case, you only needs to guess the 3-digit CVV first. With 1,000 possible combinations, you can easily try all options (brute force) to determine the correct CVV. Once the CVV is correct, the system sends an OTP (one-time password), adding a second layer of security.
• Cracking the 6-digit OTP (1,000,000 combinations) after the CVV increases the total combinations to 1,001,000.
• You can isolate the two steps (guess CVV first, then OTP), the process becomes faster, making the system less secure.

Case 2: OTP Sent Even If CVV is Incorrect

Here, both the CVV (3 digits) and OTP (6 digits) must be correct in one attempt, resulting in a total of 10^9 combinations (1 billion). This increases the time and effort required for brute-force attacks by 1,000 times, making the system significantly harder to compromise.

To minimize the risk of CVV bypass or brute-force attacks, consider the following measures:

Limit Attempt Rates:

• Implement strict rate-limiting for CVV and OTP guesses.
• Block or flag accounts after a set number of failed attempts.

Multi-Factor Authentication (MFA):

Require additional verification beyond OTP, such as biometric checks or app-based authentication.

Encrypt CVV Data:

Never store CVV codes as per PCI DSS guidelines. This reduces exposure during data breaches.

Tokenization:

Use tokens for card transactions instead of exposing raw card data during verification processes.

Dynamic CVV:

Introduce dynamic CVVs that change with each transaction using app-based solutions or hardware devices, making brute-force attacks nearly impossible.