If you never requested https://localhost:11501 and suspect a conflict, find and kill the process:

Then restart your intended dev server on its default port.

Let’s get practical. Here’s how to intentionally create and use this URL in popular tools.

Many dev servers now enable HTTPS by default or via a flag:

These servers often pick random available ports, and 11501 is a common free port.

If you used an old self-signed certificate on port 11501, it might use weak RSA keys (512-bit) or MD5 hash – vulnerable to downgrade attacks. Always generate fresh certs with mkcert or OpenSSL with at least 2048-bit keys.

  • Server Configuration:

  • Security Headers:

  • Vulnerabilities:

  • Best Practices:

  • Observations and Recommendations:

    • Some firewalls block high ports for loopback traffic, especially on Windows. Temporarily disable Windows Defender Firewall or add an inbound rule for port 11501 to test.

    Some common apps use port 11501:

    Stop the conflicting service or change your app’s port.