Why should I disable this port?
Apple enable this port by default if you want Wi-Fi Sync. The problem is, I (and probably you) never used this so this port should not be open. Enabling this port by default is a security risk as there is always an undocumented service (lockdownd) listening on this port.
This is an non-exhaustive list of what you are exposing to if you don't close this port:
- If an attacker get the pairing keys of your iDevice, he can dump the whole content of your device transparently as soon as he is on the same network as you (at Home, Work, in a Café, in a Fast Food etc) or if he have access to your cellular network (yes, the port is open on all interfaces including cellular) e.g. if the NSA have access to AT&T network or if DGSE have access to Orange network (which is true: http://www.france24.com/fr/20140320-dgse-renseignement-espionage-nsa-donnees-operateur-orange-snowden/ ) or even if your neighbor have set up a IMSI-Catcher.
- It make the iOS device easily identifiab