Open a port but no service.
 

Hello.
Can open a port but no service run on it cause a security problem? Nmap can detect that port is open but no service run on it.

Thank you.

Are you sure there are no service running? You can check it with the following code:

Sorry, no...ports don't 'open' unless a service is running to actually OPEN IT. Does this tie in with your (going on five) other threads now about some generic security issue???

Well the OP probably means “open in the firewall”.

Should not be a problem, until somebody runs a listener by mistake or malice. Normally there is no reason to leave unused ports open in the firewall, so the question is somewhat moot, I think.

While I don't disagree with your analysis, I'd suggest there's not much hope of guessing what this OP "probably" means about anything.

Note that if one isn't running a firewall at all, all ports are "open," but as you say, there's no harm if nothing is listening on the open port.