What is an open port and why should I check them?

An open port is a network communication endpoint configured on your server to accept incoming connections. While web servers must keep port 80 (HTTP) and port 443 (HTTPS) open, inadvertently leaving internal database or management ports open allows anyone on the internet to attempt unauthorized logins or exploit daemon vulnerabilities.

What is the difference between Open, Closed, and Filtered (Stealth) ports?

Open means a service accepted the connection. Closed means the server responded with RST indicating no service is listening. Filtered (Stealth) means a firewall dropped or intercepted the packet without responding, making it invisible to attackers.

Why is it dangerous to leave MySQL (3306), Redis (6379), or MongoDB (27017) open?

Database services are designed for private, internal application traffic. When exposed to the public internet, automated botnets and ransomware worms scan for them relentlessly. Older Redis instances lack authentication by default, and misconfigured MongoDB or MySQL instances are frequently wiped and replaced with ransom notes within hours of exposure.

How do I close or block an open port on Ubuntu / Debian using UFW?

You can block any exposed port using UFW: sudo ufw deny 3306/tcp to block public access, or sudo ufw allow from YOUR_IP to any port 3306 proto tcp to restrict access to a trusted static IP. Then run sudo ufw enable.

How do cloud security groups (AWS, DigitalOcean, GCP) protect ports?

Cloud security groups operate as hypervisor-level virtual firewalls outside your operating system. By default, cloud security groups should enforce a Default Deny policy, only explicitly allowing ports 80 and 443 for public web traffic, and restricting SSH (port 22) to specific static IPs or VPNs.

Firewall & Port Defense Suite

Free Open Port Checker & Firewall Scanner

Check whether common TCP ports respond from our server. Review web ports (80, 443) and ports often used by databases (MySQL 3306, PostgreSQL 5432, Redis 6379, MongoDB 27017). A connection alone cannot identify the service or prove firewall safety.

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Open Port & Firewall Checker

Scan your server for publicly exposed ports. Verify standard web ports (80, 443) and ensure sensitive database ports (MySQL 3306, Postgres 5432, Redis 6379, MongoDB 27017) and remote admin ports (SSH, RDP) are shielded behind a firewall.

Why open database ports are dangerous

Automated botnets scan the entire IPv4 range every minute searching for open database ports (like Redis 6379 and MongoDB 27017). Unfirewalled databases are routinely held for ransom or wiped within hours of exposure.

Your port scan results will appear here

Enter your domain or server IP above to probe web, database, and administration ports with instant firewall status.

Why Regular Port Auditing is Critical for Cloud Servers

In modern DevOps and cloud deployments (AWS, DigitalOcean, Hetzner, Google Cloud), developers frequently launch Docker containers, microservices, and databases. Without rigorous firewall rules, containers can inadvertently bind to 0.0.0.0 instead of 127.0.0.1, exposing internal services to the entire internet.

Running external port scans verifies your server's perimeter security from an attacker's perspective, confirming whether your cloud security groups and OS firewalls are functioning as expected.

The High-Risk Port Danger Matrix

These ports should NEVER be exposed to the public internet without a VPN or IP whitelist:

Port 6379 (Redis) & 27017 (MongoDB)

Extremely vulnerable to automated data wiping and ransomware worms. Redis must be bound to localhost or protected with strong AUTH.

Port 3306 (MySQL) & 5432 (PostgreSQL)

Routinely subjected to massive dictionary brute-force attacks. Database servers should only communicate with backend APIs over private VPC networks.

Port 22 (SSH)

Commonly exposed for server administration. If left public, disable password authentication, use key pairs, and install Fail2ban.

Port 3389 (Windows RDP)

Windows Remote Desktop is historically prone to critical exploits (like BlueKeep). Restrict access behind an SSL VPN gateway.

Server Port Hardening Checklist

1. Adopt a "Default Deny" Policy: Configure your firewall to drop all incoming packets on every port by default, and only open ports 80 and 443 explicitly.

2. Bind Databases to Localhost: In your redis.conf, my.cnf, or mongod.conf, set bind 127.0.0.1 to prevent network exposure.

3. Use Tailscale or WireGuard for Remote Management: Instead of opening port 22 or 3389 to the world, access your internal servers through an encrypted mesh VPN.

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Frequently Asked Questions About Open Ports

Everything you need to know about port states, firewall rules, and database protection.

An open port is an active network communication gateway listening on your server to accept incoming packets. While web applications must keep port 80 (HTTP) and port 443 (HTTPS) open to serve web pages to visitors, leaving internal ports (such as MySQL, Redis, or SSH) open to the public internet exposes your backend to automated credential brute-forcing, data theft, and zero-day exploits.