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As for closing it, have you checked your firewall and how it is configured? Don't know about linux, but once upon a time in Windows, a fairly annoying little program kept a port open in my firewall. I'm not sure if that's possible in linux. Depends a lot on your firewall.
PORT STATE SERVICE
37/tcp open time
53/tcp open domain
80/tcp open http
113/tcp open auth
135/tcp filtered msrpc
137/tcp filtered netbios-ns
138/tcp filtered netbios-dgm
139/tcp filtered netbios-ssn
445/tcp filtered microsoft-ds
623/tcp filtered unknown
This thread is Google's top hit for port 623, so I'm adding useful information.
It's used by Intel's vPro/AMT/MBeX suite of technology, wherein a KVM is integrated with the motherboard, allowing remote access to the system regardless of the state of the OS -- or even if there's none.
That's why you don't see it in the netstat output, the OS isn't listening, the hardware is.
I dunno if the OS firewall will stop it, I haven't tested yet. I don't even know which behaviour I prefer, if the OS can control it or if the hardware wins.
It's intended for central management by corporate helpdesks and so on, and I'm looking for decent free or open source software to use with it.
FreakWent is right. This port is open by the NIC itself as part of lights out management. While it's not really a problem to leave this port open if there is some kind of security issue in your vendors particular implementation of LOM then an attacker would have access to reboot your system among other low level commands.
If you wanted to disable this you'd most likely have to reboot and after the bios screen look for your nic to announce how to configure it. It may say something like PXE boot but there should be some kind of keyboard combo that'll get you directly into the nics settings. From there you can usually disable LOM.
Alternatively, you can put LOM on another subnet so that you don't even see it on a portscan of your main ip.
But to distribute machines to consumers with these ports open is grossly negligent, IMNSHO.
And to not even tell the consumer at all? Wow.
That's just wrong as windows raining down.
I'm all for IPMI implementations, but this is just completely irresponsible.
What makes it even worse, is that this thread is at the top of the google hits - meaning, there's a whole world of people running this model machine just waiting for a 0day whackattack, because no one knows they're potentially vulnerable.
Next we'll be hearing that these machines have a factory default set of credentials enabled on the listening ports.
Finally, it's definately NOT kewl for a manufacturer to so prominently use low port numbers for such things - without first registering those ports.