Path Traversal Detection Regex for JavaScript

What this pattern does

This page provides a well-structured, multi-part regular expression for matching path traversal detection, ported and verified for JavaScript. A rigorously tested regex reduces debugging time and protects your application from edge-case failures. 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

// Path Traversal Detection
// ReDoS-safe | RegexVault — Dev & Systems > File Paths

const pathTraversalDetectionRegex = /(?:^|[\/\\])\.\.[\/\\]|(?:^|[\/\\])\.[\/\\]|(?:^|[\/\\])\.\.($)/;

function validatePathTraversalDetection(input: string): boolean {
  return pathTraversalDetectionRegex.test(input);
}

// Example
console.log(validatePathTraversalDetection("../etc/passwd")); // true

Test Cases

When to use this pattern

This pattern is drawn from the Dev & Systems > File Paths 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

MATCH indicates traversal was found — use as a BLOCK pattern. Normalize paths with realpath() before this check to prevent double-encoding bypass.