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Port 502 Details

known port assignments and vulnerabilities
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Port(s) Protocol Service Details Source
502 tcp asa-appl-proto Phoenix Contact FL IL 24 BK-PAC allows remote attackers to cause a denial of service (hang) via unspecified manipulations as demonstrated by a Nessus scan or (2) malformed input to TCP port 502.
References: [CVE-2008-7199]

The modbus_125_handler function in the Schneider Electric Quantum Ethernet Module on the NOE 771 device (aka the Quantum 140NOE771* module) allows remote attackers to install arbitrary firmware updates via a MODBUS 125 function code to TCP port 502.
References: [CVE-2011-4861]

Unspecified vulnerability in the Modbus/TCP Diagnostic function in MiniHMI.exe for the Automated Solutions Modbus Slave ActiveX Control before 1.5 allows remote attackers to corrupt the heap and possibly execute arbitrary code via malformed Modbus requests to TCP port 502.
References: [CVE-2007-4827] [BID-25713] [OSVDB-38259]

Triangle Research International (aka Tri) Nano-10 PLC devices with firmware before r81 use an incorrect algorithm for bounds checking of data in Modbus/TCP packets, which allows remote attackers to cause a denial of service (networking outage) via a crafted packet to TCP port 502.
References: [CVE-2013-2784]

Triangle Research International (aka Tri) Nano-10 PLC devices with firmware r81 and earlier do not properly handle large length values in MODBUS data, which allows remote attackers to cause a denial of service (transition to the interrupt state) via a crafted packet to TCP port 502.
References: [CVE-2013-5741], [OSVDB-97728], [SECUNIA-55782]

Schneider Electric Modicon TM221CE16R devices allow remote attackers to discover the application-protection password via a \x00\x01\x00\x00\x00\x05\x01\x5a\x00\x03\x00 request to the Modbus port (502/tcp). Subsequently the application may be arbitrarily downloaded, modified, and uploaded.
References: [CVE-2017-7575], [BID-97523]

The Auto-Maskin products utilize an undocumented custom protocol to set up Modbus communications with other devices without validating those devices. The originating device sends a message in plaintext, 48:65:6c:6c:6f:20:57:6f:72:6c:64, "Hello World" over UDP ports 44444-44446 to the broadcast address for the LAN. Without verification devices respond to any of these broadcast messages on the LAN with a plaintext reply over UDP containing the device model and firmware version. Following this exchange the devices allow Modbus transmissions between the two devices on the standard Modbus port 502 TCP. Impact: An attacker can exploit this vulnerability to send arbitrary messages to any DCU or RP device through spoofing or replay attacks as long as they have access to the network. Affected releases are Auto-Maskin DCU-210E RP-210E: Versions prior to 3.7 on ARMv7.
References: [CVE-2018-5400]

An issue was discovered on TENGCONTROL T-920 PLC v5.5 devices. It allows remote attackers to cause a denial of service (persistent failure mode) by sending a series of \x19\xb2\x00\x00\x00\x06\x43\x01\x00\xac\xff\x00 (aka UID 0x43) requests to TCP port 502.
References: [CVE-2019-9590], [XFDB-158222]

Carel pCOWeb HVAC could allow a remote attacker to bypass security restrictions, caused by no authentication mechanism required for Modbus interface on TCP port 502. By sending a specially-crafted request, an attacker could exploit this vulnerability to bypass access restrictions.
References: [XFDB-170822]

IANA registered for: Modbus Application Protocol, asa-appl-proto
502 tcp,udp Modbus, Protocol (unofficial) Wikipedia
502 tcp,udp mbap Modbus Application Protocol, modified: 2014-06-10 IANA
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External Resources
SANS Internet Storm Center: port 502

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. For more detailed and personalized help please use our forums.

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