Kerberos is a protocol that is used for netowrk authentication. Different versions are used by Nix and Windows. But if you see a machine with port 88 open you can be fairly certain that it is a Windows Domain Controller.
If you already have a login to a user of that domain you might be able to escalate that privilege.
MS14-068
## Port 110 - Pop3
This service is used for fetching emails on a email server. So the server that has this port open is probably an email-server, and other clients on the network (or outside) access this server to fetch their emails.
@@ -527,6 +534,15 @@ Outgoing smtp-port
If Postfix is run on it it could be vunerable to shellshock
https://www.exploit-db.com/exploits/34896/
## Port 631 - Cups
Common UNIX Printing System has become the standard for sharing printers on a linux-network.
You will often see port 631 open in your priv-esc enumeration when you run **netstat**. You can log in to it here: **http://localhost:631/admin**
You authenticate with the OS-users.
There are vulnerabilites for it so check your searchsploit.
