How to Discover and Secure Open Port Vulnerabilities

Open Port Vulnerabilities: What's the Big Deal?

Open port vulnerabilities pose a significant security risk to your organization. If left exposed, ports are a gateway for hackers to breach your network and steal your data.

But what are open ports, why are they a security risk, and what can you do to close open port vulnerabilities?

Let’s answer your open port questions.

What are open ports?

All communication that happens over the internet is exchanged via ports. These virtual communication endpoints help computers—from your laptop to the cloud—understand what to do with internet-based traffic.

How do ports work?

Every device that connects to the internet is given a unique identifier called an IP address. Each IP address contains two kinds of ports, TCP and UDP. Think of these as doors that can receive information. There are lots of these doors—up to 65,535 of each for any given IP address. One port sends email traffic to your inbox (either a POP3, IMAP, or SMTP port) and another (a web server port) handles website traffic and so on.

Ports need to be open so they can receive information or packets of data and for everything to work smoothly. If a port is closed it will reject or ignore packets. It’s like not answering the door when someone comes knocking.

Why are open ports dangerous?

Open ports are the building block of internet communication and in themselves are not a security risk. However, hackers can use vulnerable, unpatched, misconfigured, or infected underlying services in conjunction with open ports to move laterally across the network and gain access to sensitive data. For example, the notorious WannaCry ransomware attack spread through ports that were mistakenly left open.

Indeed, studies have shown that open ports pose a high security risk:

  • A study by Marsh McLennan compared the security performance data of thousands of organizations that experienced cybersecurity incidents against those that did not and found that open ports are strongly correlated with the risk of cyberattacks.
  • Reinforcing these findings, Bitsight researchers found that organizations with an open port grade of F are more than twice as likely to experience a breach as companies with an A grade. If Bitsight can see this information, that means cyber criminals can too.
BitSight Open Port Grades and Breach Correlation graph

What can you do to fix open ports?

CIS Critical Security Controls list open ports as a substantial network risk and recommends that only those ports with a valid business requirement—such as those associated with a legitimate service—are left open or running on a system.

System administrators can use port scanners or vulnerability scanners to discover and close open ports that are exchanging information on their networks. However, closing open ports requires knowing which ports are required by the services running on a network. Some of these are universal—for example, port 80 is the port for web traffic (HTTP). Others are reserved by specific services. Many scanning tools provide information about whether the open port is in use.

Once the administrator knows which ports must remain open, they can conduct a scan to identify open ports that might be exposing their systems to cyberattacks. If a port is open and not associated with any known service on the network, it should be closed immediately.

How can you monitor open ports?

Closing open ports isn’t that big of a task on a small network with relatively few IP addresses. However, monitoring and managing open ports on larger networks with a constant flow of new devices can be extremely time-consuming. In addition to the ports themselves, the services exchanging information through those ports should be monitored to ensure they are patched, configured correctly, and not infected with malware.

Besides port scanning tools, here are some tips to discovering open ports and open port vulnerabilities and ensuring port security:

  • Understand your external attack surface: Start by establishing the lay of the land. Scan your external attack surface so that you can visualize your digital ecosystem­—on-premise, in the cloud, and across geographies and remote locations—the way a hacker does. Look for a solution that offers dashboard views so you can quickly map and inventory your internet-facing digital assets (including open ports and services), understand their exposure, prioritize remediation, and close the door on threat actors.
  • Continuously monitor for emerging risks: Your digital environment is constantly changing. New services are being spun up, remote employees are connecting to the network, and new vendors are being onboarded. Because of this, it’s a good idea to continuously monitor the cyber health of your digital environment. Go beyond point-in-time penetration testing or security audits and look for a solution that provides automatic and continuous insights into gaps like open ports, misconfigured software, unpatched systems, and more.
  • Grade your open port performance: An open port grade is an important cybersecurity KPI. It indicates how well your network is sealed against intrusion attempts. For example, Bitsight Security Ratings grade open port vulnerabilities from A to F. The grade is automatically generated, updated daily, and reflects performance compared to other organizations in the same industry.
  • Maintain a regular patching cadence: Make sure you install software updates and patches as soon as they're released. This will protect you from threat actors who continuously scan the internet for vulnerable systems.

Close the door on cyber criminals

Open ports can increase your organization’s risk of data breach. By performing a few initial scans, establishing an external attack surface management strategy, and setting up a continuous security monitoring tool, this risk vector can be virtually eliminated.

Compared to other, more complex security issues, open port vulnerabilities are easy to mitigate, and doing so is part of practicing good cybersecurity hygiene.