A database file that stores Active Directory (AD) data such as user and Group Objects, Group membership, and password hashes for all users in the Domain.
It is stored on a Domain Controller (DC) at C:\Windows\NTDS\.
Vulnerability
Once an attacker obtain full access to a Domain this file provides access to the password hashes of all users in the domain, which can be cracked.
Furthermore if the setting ‘Store passwords using reversible encryption’ is enabled (which is sometimes done to allow applications or protocols access to users password) then NTDS.DIT will also store the cleartext password of all users to created or changed their password when this setting was enabled.