I’ve read an article which describes how to simulate the close ports as open in Linux by eBPF. That is, an outside port scanner, malicious actor, will get tricked to observe that some ports, or all of them, are open, whereas in reality they’ll be closed.
How could this be useful for the owner of a server? Wouldn’t it be better to pretend otherwise: open port -> closed?
What extra information could you gather? Note I assume we are talking about a fake open port here, not an active service listening on a port that can communicate with the attacker. That could be done without eBPF though - so what advantage would eBPF have here?
And I assume this is more on the level of responding to pings than creating full connections? At which point you are only dealing with a single packet from the sender. So what value does responding give you here?
At a guess, you might tell the difference between some benign scan and an attempt to actually take advantage of the port, perhaps to use as a trigger to automatically ban an ip address? or a way to divert malicious resources to an easy looking target so they are less available in other areas?
The difference between someone scanning for open ports and someone attacking a port they find open seems significant enough to at least track and watch for patterns… Whether that’s useful for the majority of users or not is rarely why a feature is implemented.
What is a benign scan? Why do you need to scan a system if you are not trying to figure out what it is running - which is something only attackers or the server admins (looking for things that should not be exposed) would want to do. Any third party scanning for open ports I would consider an attack. Though it might just be an automated system looking for weaknesses - it is still an attack.
A benign scan could just be looking for an ftp server to connect to or a repeater or relay server of some sort. There are plenty of open services people make available for free and the fact that you would consider it an attack it doesn’t make it one.
At minimum you could be alerted to look for someone attempting to connect to your ftp server with a single basic anonymous authentication vs someone flooding that port with known malicious software attacks, and block the latter across your entire network and effectively ignore the former. Really it seems like you’re advertising your lack of imagination in this context than a legitimate lack of possible uses for spoofing open ports.
port knocking maybe?
Port knocking does not require open ports though? It works by trying to connect to closed ports in a specific sequence does it not?
or maybe fake ports?
What is a fake port?