X-Frame-Options Header Regex for Python

What this pattern does

This page provides a well-structured, multi-part regular expression for matching x-frame-options header, ported and verified for Python. In security-sensitive code, using an unverified regex can open the door to both false positives and denial-of-service attacks. 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

# X-Frame-Options Header
# ReDoS-checked | RegexVault — Security > Security Headers

import re

xframeoptions_header_pattern = re.compile(r'^(?:DENY|SAMEORIGIN|ALLOW-FROM\s+https?://[^\s]+)$')

def validate_xframeoptions_header(value: str) -> bool:
    return bool(xframeoptions_header_pattern.fullmatch(value))

# Example
print(validate_xframeoptions_header("DENY"))  # True

Test Cases

When to use this pattern

This pattern is drawn from the Security > Security Headers category and has been checked for ReDoS risk. 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

X-Frame-Options prevents clickjacking by controlling iframe embedding. DENY: never in iframe. SAMEORIGIN: iframe on same origin only. ALLOW-FROM: deprecated (not supported by Chrome/Firefox). Modern alternative: CSP frame-ancestors directive, which is more flexible and widely supported.