X.509 Certificate Serial Number Regex for JavaScript

What this pattern does

This page provides a well-structured, multi-part regular expression for matching x.509 certificate serial number, 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.509 Certificate Serial Number
// ReDoS-safe | RegexVault — Security > Certificates & PKI

const x509CertificateSerialNumberRegex = /^[0-9a-f]{2}(?::[0-9a-f]{2}){7,19}$/i;

function validateX509CertificateSerialNumber(input: string): boolean {
  return x509CertificateSerialNumberRegex.test(input);
}

// Example
console.log(validateX509CertificateSerialNumber("01:23:45:67:89:ab:cd:ef:01:23:45:67:89:ab:cd:ef")); // true

Test Cases

When to use this pattern

This pattern is drawn from the Security > Certificates & PKI 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.509 serial numbers are 1-20 byte (8-160 bit) integers, typically displayed in colon-separated hex pairs. CA/Browser Forum requires serial numbers be at least 64 bits and generated with at least 64 bits of entropy. Used for certificate revocation lookups (CRL, OCSP).