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Active Directory's backdoor: Ownership

Ownership is a concept that is often overlooked, pushed aside, or outright forgotten when the security infrastructure of a network is designed and implemented. This is a serious problem. Ownership serves as a mechanism for creators of new resource objects to have full control over those objects. As a user right, specifically the take ownership right, it grants some user accounts the ability to bypass just about any security restriction. Obviously, this is a

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backdoor that needs to be properly addressed and secured.

When users create new objects, such as folders, Word documents, image files, etc. the user account is assigned as the owner of that object. In effect, the creator of an object is the objects owner, at least initially. Unless ownership changes hands, the original creator retains full control over that object. As an object's owner, a user account can change any aspect of that object, including redefining access permissions and auditing. This is typically not a problem when those objects are within a user's home directory. However, when those objects become distributed throughout a network, especially on centralized file servers, distributed ownership can work against the greater good - i.e. maintaining consistent security restrictions and access control. As a regular administrative task, the designated primary administrator for each file system host should take ownership of all files on the shared volumes. In this way, some semblance of centralized and consistent control can be maintained across the enterprise.

The user right of taking ownership is another serious area that needs addressing. Members of the Administrators group by default have this user right. For the most part, that makes sense. If for whatever reason an object is improperly configured so that no-one can access it (such as setting Deny to the Everyone group), an administrator can take ownership then re-configure the object's permissions. But, in large and complex networks, it is worth watching to see if the Take Ownership user right is being abused. If this backdoor is being used for purposes other than emergencies, you may need to reconsider who you've granted administrative privileges to.

As for Active Directory itself, it is important for the correct service administrator account or service administrator groups in each domain to be the owner of the root for their directory partition. Ownership of a domain root grants that user (or group) complete and full access to all objects within that directory partition. So, ensure that the Schema Administrators group owns the schema directory partition, the Enterprise Administrators group owns the configuration directory partition, and the Administrators group owns the domain directory partition.


James Michael Stewart is a partner and researcher for ITinfopros, a technology-focused writing and training organization.


 

This was first published in June 2004

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