CVV / CVC / Security Code Regex for Python

What this pattern does

This page provides a lightweight, single-purpose regular expression for matching cvv / cvc / security code, ported and verified for Python. Financial data validation has zero tolerance for false negatives — a missed invalid entry can corrupt downstream calculations. The snippet below is ready to drop into your Python project — whether you're validating in a Django view, a FastAPI endpoint, or a standalone data processing script.

Python Implementation

# CVV / CVC / Security Code
# ReDoS-safe | RegexVault — Finance > Card Numbers

import re

cvv_cvc_security_code_pattern = re.compile(r'^[0-9]{3,4}$')

def validate_cvv_cvc_security_code(value: str) -> bool:
    return bool(cvv_cvc_security_code_pattern.fullmatch(value))

# Example
print(validate_cvv_cvc_security_code("123"))  # True

Test Cases

When to use this pattern

This pattern is drawn from the Finance > Card Numbers category and carries a ReDoS-safe certification. That matters for Python developers because particularly important in Python web servers where CPU-bound regex operations can stall concurrent request handling. RegexVault audits patterns against known backtracking attack vectors, ensuring you have the necessary context before using this regex in a high-stakes production environment.

Common Pitfalls

Technical Notes

CVV (Visa), CVC (Mastercard), CID (Amex) are 3 digits on the back for Visa/MC/Discover, 4 digits on the front for Amex. PCI-DSS prohibits storing CVV/CVC post-authorization — never persist this value.