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Port 139 Details

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Port(s) Protocol Service Details Source
139 tcp,udp netbios-ss NetBIOS is a protocol used for File and Print Sharing under all current versions of Windows. While this in itself is not a problem, the way that the protocol is implemented can be. There are a number of vulnerabilities associated with leaving this port open.

NetBios services:
NETBIOS Name Service (TCP/UDP: 137)
NETBIOS Datagram Service (TCP/UDP: 138)
NETBIOS Session Service (TCP/UDP: 139)

By default, when File and Print Sharing is enabled it binds to everything, including TCP/IP (The Internet Protocol), rather than just the local network, meaning your shared resources are available over the entire Internet for reading and deletion, unless configured properly. Any machine with NetBIOS enabled and not configured properly should be considered at risk. The best protection is to turn off File and Print Sharing, or block ports 135-139 completely. If you must enable it, use the following guidelines:

1. Use strong passwords, containing non-alphanumeric characters.
2. Attach "$" at the end of your share names (the casual snooper using net view might not see them).
3. Unbind File and Print Sharing from TCP/IP and use NetBEUI instead (it's a non-routable protocol).
4. Block ports 135-139 in your router/firewall.

Keep in mind that you might still be leaking out information about your system that can be used against you (such as your computer and workgroup names) to the entire Internet, unless ports are filtered by a firewall.

There is also a Critical Windows RPC vulnerability affecting ports 135,139 and 445, as detailed here: MS Technet Security Bulletin [MS03-026]

The following trojans/backdoors also use these ports:
Chode, God Message worm, Msinit, Netlog, Network, Qaz

W32.HLLW.Moega [Symantec-2003-080813-3234-99]

W32.Reidana.A [Symantec-2005-032515-4042-99] (2005.03.27) - worm that spreads using the MS DCOM RPC vulnerability (MS Security Bulletin [MS03-026]) on port 139. The worm attempts to download and execute a remote file via FTP. Opens TCP port 4444.

W32.Klez worm [Symantec-2002-031910-1028-99] - a class of worms that collects email addresses from an infected computer's Windows address book and propagates using its own SMTP server. As of April 26, 2002, there are nine variants of the Klez worm that all exploit the "Microsoft Internet Explorer Incorrect MIME header" vulnerability, which causes an email attachment to be automatically executed when an HTML email is previewed by a Microsoft Outlook or Outlook Express user. The worm can arrive as an email attachment with one of the following file extensions: asp, bak, c, cpp, doc, htm, html, jpg, mp3, mpg, mpeg, pas, rtf, wab, or xls.

W32.Sircam.Worm [Symantec-2001-071720-1640-99] - a computer worm that propagates by e-mail from Microsoft Windows systems. It also spreads via open shares on a network. Sircam scans the network for computers with shared drives and copy itself to a machine with an open (non-password protected) drive or directory.

Buffer overflow in a certain driver in Cisco Security Agent 4.5.1 before, 5.0 before, 5.1 before, and 5.2 before on Windows allows remote attackers to execute arbitrary code via a crafted SMB packet in a TCP session on port (1) 139 or (2) 445.
References: [CVE-2007-5580] [BID-26723] [SECUNIA-27947] [OSVDB-39521]

Server Message Block (SMB) also uses this port. It is used by Microsoft Windows file and print services, such as Windows Sharing in Mac OS X.
139 tcp,udp NetBIOS NetBIOS Session Service (official) Wikipedia
139 tcp trojan Chode, Fire HacKer, Msinit, Nimda, Opaserv, Qaz Trojans
139 tcp Chode [trojan] Chode Neophasis
139 tcp GodMessageworm [trojan] God Message worm Neophasis
139 tcp Msinit [trojan] Msinit Neophasis
139 tcp Netlog [trojan] Netlog Neophasis
139 tcp Network [trojan] Network Neophasis
139 tcp Qaz [trojan] Qaz Neophasis
139 tcp Sadmind [trojan] Sadmind Neophasis
139 tcp SMBRelay [trojan] SMB Relay Neophasis
139 tcp threat God Message worm Bekkoame
139 tcp threat Msinit Bekkoame
139 tcp threat Netlog Bekkoame
139 tcp threat Network Bekkoame
139 tcp threat Qaz Bekkoame
139 tcp threat W32.Cissi Bekkoame
139 tcp threat W32.HLLW.Deborms Bekkoame
139 tcp threat W32.HLLW.Moega Bekkoame
139 tcp threat W32.Kiman Bekkoame
139 tcp threat W32.Licum Bekkoame
139 tcp threat W32.Reidana Bekkoame
139 tcp threat W32.Spybot Bekkoame
139 tcp threat W32.Yaha Bekkoame
139 tcp,udp netbios-ssn NETBIOS Session Service IANA
25 records found
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Related ports: 135  137  138  445  4444  

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External Resources
SANS Internet Storm Center: port 139

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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