Is port 502 (Modbus) dangerous?

Port 502 is classified as critical risk and should not be exposed to the public internet. It transmits data without encryption, making it vulnerable to eavesdropping and credential theft.

Should port 502 be open on my firewall?

No, port 502 should not be open to the public internet. Block it at the firewall and use encrypted alternatives such as SSH, SFTP, or HTTPS instead.

What transport protocol does port 502 use?

Port 502 (Modbus) uses the TCP transport protocol and falls under the Other category.

:502 (TCP)

Modbus

Critical Risk

TCP — Other

Port Overview

Port Number 502

Service Name Modbus

Transport Protocol TCP

Category Other

Security Risk Critical

Port Range Well-Known (0-1023)

What is Port 502?

Port 502 is assigned to Modbus, widely used in industrial control systems (ICS), SCADA systems, and PLCs. No built-in authentication. Internet exposure is extremely dangerous.

TCP Other Commonly Used

Security Considerations

Port 502 (Modbus) is classified as critical risk. This port should not be exposed to the public internet. The service transmits data without encryption, making it vulnerable to eavesdropping, credential theft, and man-in-the-middle attacks.

Recommendation: Block this port at the firewall. Use encrypted alternatives (SSH, SFTP, HTTPS) instead.

Related Ports — Other

35 Private Printer Server 43 WHOIS 63 Whois++ 75 Private Dial-Out Service 78 VetTCP 91 MIT-DOV 92 NPP 104 DICOM

Related Terms

ASN BGP Hijack Data Center Domain Name Dual Stack Internet Exchange Point (IXP)