Wrong files permissions on entire server

Hi to all guys, I write because I urgently need your help.

My brother have entered a wrong command and started the following command:
chmod 777 /


When I noticed his mistake I immediately stopped the process but many files and folders now have the 0777 permissions.


Kindly tell me how I can fix it?

Please make me a list of all files that must have permissions 0644 and of all folders that must have 0755 permissions.


Please, I'm in despair and I'm afraid to change permissions to some files that I do not have to do... doing an irreparable damage.


Thank you in advance