X-Frame-Options Header Regex for JavaScript

What this pattern does

This page provides a well-structured, multi-part regular expression for matching x-frame-options header, ported and verified for JavaScript. 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 JavaScript project — whether you're validating in an Express middleware, a Next.js API route, or a client-side form.

Javascript Implementation

// X-Frame-Options Header
// ReDoS-safe | RegexVault — Security > Security Headers

const xframeoptionsHeaderRegex = /^(?:DENY|SAMEORIGIN|ALLOW-FROM\s+https?:\/\/[^\s]+)$/i;

function validateXframeoptionsHeader(input: string): boolean {
  return xframeoptionsHeaderRegex.test(input);
}

// Example
console.log(validateXframeoptionsHeader("DENY")); // true

Test Cases

When to use this pattern

This pattern is drawn from the Security > Security Headers category and carries a ReDoS-safe certification. That matters for JavaScript developers because especially critical in long-running Node.js event loops where a ReDoS vulnerability can block the entire process. 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.