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Port 503 Details
known port assignments and vulnerabilities
threat/application/port search:
| Port(s) |
Protocol |
Service |
Details |
Source |
| 503 |
tcp,udp |
intrinsa |
A denial of service vulnerability exists in the Modbus TCP and Modbus RTU over TCP USB Function functionality of Socomec DIRIS Digiware M-70 1.6.9. A specially crafted network packet can lead to a denial of service. An attacker can send an unauthenticated packet to trigger this vulnerability.This vulnerability is specific to the malicious message sent via Modbus RTU over TCP on port 503.
References: [CVE-2025-55222]
A denial of service vulnerability exists in the Modbus TCP and Modbus RTU over TCP functionality of Socomec DIRIS Digiware M-70 1.6.9. A specially crafted series of network requests can lead to a denial of service. An attacker can send a sequence of unauthenticated packets to trigger this vulnerability.An attacker can trigger this denial-of-service condition by sending a single Modbus TCP message to port 503 using the Write Single Register function code (6) to write the value 1 to register 4352. This action changes the Modbus address to 15. After this message is sent, the device will be in a denial-of-service state.
References: [CVE-2025-54851], [CVE-2025-54850]
Intrinsa (IANA official) |
SG
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| 503 |
udp |
intrinsa |
intrinsa |
Nmap
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| 503 |
tcp,udp |
intrinsa |
Intrinsa |
IANA
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3 records found
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Related ports: 502
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External Resources
SANS ISC: port 503
Notes:
Port numbers in computer networking represent communication endpoints. Ports are unsigned 16-bit integers (0-65535) that identify
a specific process, or network service. IANA is responsible for internet protocol resources, including the registration of commonly
used port numbers for well-known internet services.
Well Known Ports: 0 through 1023.
Registered Ports: 1024 through 49151.
Dynamic/Private : 49152 through 65535.
TCP ports use the Transmission Control Protocol, the most commonly used protocol
on the Internet and any TCP/IP network. TCP enables two hosts
to establish a connection and exchange streams of data. TCP guarantees delivery of data
and that packets will be delivered in the same order in which they were sent.
Guaranteed communication/delivery is the key difference between TCP and UDP.
UDP ports use the Datagram Protocol. Like TCP, UDP is used in combination with IP (the Internet Protocol)
and facilitates the transmission of datagrams from one computer to applications on another computer,
but unlike TCP, UDP is connectionless and does not guarantee reliable communication; it's up to the application that received
the message to process any errors and verify correct delivery. UDP is often used with time-sensitive
applications, such as audio/video streaming and realtime gaming, where dropping some packets is preferable to waiting for delayed data.
When troubleshooting unknown open ports, it is useful to find exactly what services/processes are listening to them.
This can be accomplished in both Windows command prompt and Linux variants using the "netstat -aon" command.
We also recommend runnig multiple anti-virus/anti-malware scans to rule out the possibility of active malicious software.
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