Are Open Ports Dangerous?
Learn what open ports are, if they are dangerous, and how to reduce a server's attack surface.
Table of Contents 📖
What is an Open Port?
Open ports are ports that accept external traffic, allowing communication with the technologies that are running on that port. For example, a web server running on port 80 accepts user connections and sends back the web application content. Open ports are necessary for users to connect to remote services. If port 80 was closed, then users would not be able to access the web application.
INFO: A port isn't open if there isn't a service listening for a connection on it.
Are Open Ports Dangerous?
Open ports provide an opportunity for an attacker to exploit vunlerabilities. In other words, an open port is an attack surface. This means that the service listening on the port could be vulnerable to an attack. For example, if Nginx is running on port 80 and has a known vulnerability, attackers can attempt to exploit it. However, as mentioned previously, open ports are required to have users connect to an application.
WARNING: Unencrypted protocols running on an open port are vunlerable to leaking sensitive information. For example, transfering passwords in clear text can be viewed by an attacker.
Lowering Attack Surface
Whenever we are building an application, we want to reduce the attack surface. As open ports provide an attack surface, they should only be open when required. For example, having a database port open to the public is not necessary and can lead to an attack. Therefore, we should write a firewall rule to block the database port or whitelist only the necessary IP addresses.
INFO: Firewalls exist to control who is allowed to connect to certain ports, reducing the attack surface.