Glossary Glossary

Open Port




An open port is an external-facing asset configured to accept incoming connections. Ports are numbered from 1 to 65535, each of which is associated with a specific service or application. Some ports must be kept open since they are used for specific Internet-related services. For example, port 80 has to be kept open to allow incoming and outgoing HyperText Transfer Protocol (HTTP) connections. On the other hand, port 25 needs to be kept open to enable users to relay messages from one email server to another.

However, open ports can be security risks if improperly secured. Attackers can exploit these digital assets to access related systems and files. Therefore, unsecured open ports are part of an organization’s attack surface.

Table of Contents

Open Port: A Deep Dive

How Do You Identify Open Ports?

You can use a port scanner to determine which ports are open. These tools scan computers or networks for open ports by sending packets to them and see if they respond.

Since attackers can exploit open ports, scanning for them is recommended. Companies often employ attack surface management (ASM) platforms to automatically detect, catalog, and monitor Internet-exposed assets, including open ports.

Is Leaving Ports Open Dangerous?

An open port can serve as an entry point for attackers to gain access to computers. Threat actors typically probe for open ports to see which services a target uses. They then identify vulnerabilities in those services or applications and exploit them to gain access.

For this reason, leaving vulnerable, unused, or unintended ports open can be dangerous. They can pave the way for malware infections, data breaches, denial-of-service (DoS) attacks, and other malicious activities and widen an organization’s attack surface.

How to Secure Open Ports

Since certain Internet services and applications require leaving ports open, it is essential to use them wisely and take protective measures against potential attacks. Below are some basic steps to secure open ports.

What Is an Open Port
  • Gain asset visibility: Ensure you have a complete and up-to-date list of all open ports. An ASM platform, for instance, automatically detects open ports and other Internet-facing assets as part of its core capabilities. It also continuously monitors a target system for any new asset and immediately detects newly opened ports.
  • Close unused ports: Examine all open ports and verify which should stay open and which should be closed.
  • Scan connected services for vulnerabilities: Use vulnerability scanners or ASM tools to check for vulnerabilities in the services and applications connected to open ports.
  • Mitigate vulnerabilities: Apply software patches or implement stringent security measures within an application dependent on open ports to reduce exploitation.
  • Use firewalls and intrusion detection and prevention systems (IDSs/IPSs): After knowing which ports must stay open, organizations typically use firewalls to monitor and, where relevant, block incoming traffic. IDSs/IPSs can also help spot malicious activity on open ports.

Like other external-facing assets, open ports need to be configured correctly for utmost security. Knowing what open ports are in your systems is the first step toward protecting them from attacks.

Key Takeaways

  • An open port is a virtual port configured to accept incoming connections.
  • It is an external-facing asset that can become a security risk if not adequately secured.
  • Port scanners and ASM platforms with asset discovery capabilities can identify open ports.
  • Threat actors typically use open ports to see what services an organization uses.
  • The first step toward protecting open ports is to identify them all.
  • Security tools like firewalls and IDSs/IPSs can also help secure open ports.

Ready to get a list of the open ports and other Internet-facing assets in your network? Schedule a free demo tailored to your organization now.

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