How I Accidentally Left a Port Open on My Linux Server (And How I Caught It) | by Faruk Ahmed | May, 2025

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How I Accidentally Left a Port Open on My Linux Server (And How I Caught It)

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Intro:

It started as a small mistake — a test service I was using for 10 minutes. But I forgot to close it. Days later, I found it still running, exposed to the internet, quietly inviting trouble. This is the story of how I caught it, how I fixed it, and what I now check regularly to make sure it never happens again.

What Happened:

I had opened port 8080 temporarily to test a Node.js web app. I meant to close it the same day — but forgot. No alerts were triggered. Days passed.

Then I ran:

sudo ss -tuln

And there it was:

LISTEN 0 128 0.0.0.0:8080 0.0.0.0:*

✅ Open on all interfaces, not just localhost. ✅ Bound to a test script still running in the background. ✅ Fully accessible from the public IP.

How I Caught It:

✅ 1. Weekly port scan from outside my network:

nmap -Pn your-server-ip

✅ 2. Local port review:

sudo ss -tuln

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