Masked Card Number (PAN Masking) Regex for Python

What this pattern does

This page provides a well-structured, multi-part regular expression for matching masked card number (pan masking), 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

# Masked Card Number (PAN Masking)
# ReDoS-safe | RegexVault — Finance > Card Numbers

import re

masked_card_number_pan_masking_pattern = re.compile(r'^[X*]{12}[0-9]{4}$|^[X*]{8}[0-9]{4}$|^[X*]{11}[0-9]{4}$')

def validate_masked_card_number_pan_masking(value: str) -> bool:
    return bool(masked_card_number_pan_masking_pattern.fullmatch(value))

# Example
print(validate_masked_card_number_pan_masking("XXXXXXXXXXXX1234"))  # 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

PCI-DSS allows displaying first 6 and last 4 digits for debugging. This pattern shows only last 4. For display in UI, use: [\*X]{8,12}[0-9]{4} adjusted for 13/15/16-digit cards.