PEM Certificate Block Regex for JavaScript

What this pattern does

This page provides a comprehensive, battle-tested regular expression for matching pem certificate block, 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

// PEM Certificate Block
// ReDoS-safe | RegexVault — Security > Certificates & PKI

const pemCertificateBlockRegex = /-----BEGIN CERTIFICATE-----[\r\n]+(?:[A-Za-z0-9+\/=\r\n]{1,80}[\r\n]+)*-----END CERTIFICATE-----/;

function validatePemCertificateBlock(input: string): boolean {
  return pemCertificateBlockRegex.test(input);
}

// Example
console.log(validatePemCertificateBlock("-----BEGIN CERTIFICATE-----
MIIBIjANBgkqhkiG9w0BAQEFAAOCAQ8AMIIBCgKCAQEA
-----END CERTIFICATE-----")); // 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

PEM format: base64-encoded DER certificate wrapped in BEGIN/END markers. Lines are max 76 characters in the standard. Use for detecting certificates in config files, code, or traffic. Parse with a proper X.509 library to extract subject, issuer, validity, and SANs.