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Port 81 Details

known port assignments and vulnerabilities
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Port(s) Protocol Service Details Source
81 udp trojans W32.Beagle.AR@mm [Symantec-2004-092811-5825-99] (2004.9.28) - mass mailing worm with backdoor functionality on port 81/tcp & udp. Affects all current Windows versions. SG
81 tcp http Hyper Text Transfer Protocol (HTTP) - ports used for web traffic. See also TCP ports 80, 8080, 8081.

Some common uses for port 81/tcp include web administration (cobalt cube), web proxy servers, McAfee Framework Service, TigerVPN (servers speed check), etc.

If you're not running web services on this port, keep in mind it is also used by some trojans:
Backdoor.Asylum [Symantec-2000-121815-0609-99] (2000.05.02) - remote access trojan, uses ports 81, 2343, 23432 by default.
W32.Beagle.AR@mm [Symantec-2004-092811-5825-99] (2004.09.28) - port 81.

Stack-based buffer overflow in the RespondeHTTPPendiente function in the HTTP server for SUMUS 0.2.2 allows remote attackers to execute arbitrary code via a large packet sent to TCP port 81.
References: [CVE-2005-1110]

RemoConChubo trojan and Blue Iris also use this port.
81 tcp Torpark - Onion routing (unofficial) Wikipedia
81 tcp trojan Asylum Trojans
81 tcp,udp hosts2-ns HOSTS2 Name Server SANS
81 tcp RemoConChubo [trojan] RemoConChubo SANS
81 tcp,udp hosts2-ns HOSTS2 Name Server Nmap
81 tcp threat W32.Beagle Bekkoame
81 tcp threat Xeory Bekkoame
81 udp threat W32.Beagle Bekkoame
81 tcp,udp Unassigned, modified: 2007-09-06 IANA
11 records found
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Related ports: 80  2343  8080  23432  

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External Resources
SANS Internet Storm Center: port 81

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.

Please use the "Add Comment" button below to provide additional information or comments about port 81.
  User Reviews/Comments:
by anonymous - 2013-06-17 05:31
TCP Port 81, used by McAfee Framework Service.
by anonymous - 2015-11-06 02:33
Used by TigerVPN to check the speed of its different servers, IP:81
This verification is made from their user's control panel.
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