Bugtraq mailing list archives
Bypassing Inherited Rights Filters in Novell Directory Services.
From: FogHorn Security <info () FOGHORNSECURITY COM>
Date: Thu, 7 Sep 2000 19:24:00 -0700
FOGHORN SECURITY ADVISORY issued September 7, 2000 http://www.foghornsecurity.com/advisories/20000907 Bypassing Inherited Rights Filters in Novell Directory Services. SUMMARY A design weakness in NDS as shipped with Novell v5.0 and later can allow certain users to bypass IRF's, and gain escalation of privileges. SEVERITY Serious. Even in a well designed tree IRF's are sometimes needed to protect more sensitive objects. This issue, if not carefully considered, can easily render IRF's ineffective, and expose sensitive information. BACKGROUND In NDS, rights are assigned in three ways: Rights to an object [Object Rights] Rights to all properties of an object [All Properties Rights] Rights to selected properties of an object [Selected Properties Rights] By default, rights granted at one level of a directory tree automatically flow down to lower levels in the tree. This inheritance of rights can be blocked by using Inherited Rights Filters [IRFs]. IRFs can be set for any of the three types of rights mentioned above. THE PROBLEM In previous versions of NDS, only Object Rights, and All Properties Rights could be inherited. In Netware 5.0, Novell added the ability to make Selected Property Rights inheritable. These rights are not blocked by IRFs set for Object Rights or All Properties Rights. They can only be blocked by the creation of an explicit IRF for each property you need to protect. Obviously, this is unworkable in the real world. Setting individual IRFs for every property in the schema is tedious and prone to error, and it is extremely difficult to anticipate all possible exploits for all properties. Additionally, if the schema is extended, the new properties would be unprotected until IRFs were updated. This also presents a problem for sites upgrading from Novell 4.11. If this issue is not addressed in the upgrade process, IRF's which were previously valid, could be rendered ineffective. EXPLOIT Active exploitation of this feature requires Write rights to the Object Trustees ACL property of a container at or above the level of the object being attacked. Here's an example. An administrator, .BOB.ACME, has Supervisor [S] rights to the .ACME container. There is a container, .SECRET.ACME, which BOB should not have any access to. Joe, .JOE.SECRET.ACME, is the administrator of .SECRET.ACME. Joe has been given S rights to SECRET, and an IRF has been put in place on SECRET blocking all Object Rights, and all All Properties Rights. This scenario is in line with standard practice, and Novell's own documentation [See TID# 10011973] Unfortunately, Bob can still gain full control of secret. 1] Bob modifies the trustees list of .ACME granting himself the Write [W] right to the Object Trustees ACL property and designates this right as inheritable. 2] Since Selected Properties Rights are not explictly blocked by the IRF at .SECRET.ACME, Bob can now add himself to the trustee list of the SECRET container and obtain full privileges. OTHER CONSIDERATIONS In addition to active exploits, this issue could result in administrators inadvertently granting rights to objects they believe to be protected by IRF's. For instance, Help Desk staff may be granted password reset rights by granting Selected Properties Rights at a high level in the tree, and making those rights inheritable. Those rights can only be blocked with an explicit Selected Properties IRF at the containers or objects you need protected. WORKAROUND It is impossible to anticipate all the scenarios where this *feature* could be exploited. Administrators should carefully evaluate their tree and permission structures with this problem in mind. At a minimum, where IRFs are used to protect objects or containers, the following properties should be protected by explicit IRFs: Object Trustees [ACL] Members Security Equal to Me Password Required Password Management Incorrect Login Attempts There are certainly others that would need to be protected as well. Finding additional exploits is left as an exercise for the reader. [Hint: Audit Objects] FIX We believe that Novell should either, a) Make IRFs set for All Properties Rights apply to Selected Properties Rights as well or b) Provide a method whereby all Selected Properties Rights could be filtered with a single IRF. COMMENTS This is a classic example of adding functionality without fully considering the implications. While we do not consider this to be a *bug*, it is clearly a poorly designed *feature*. We could not find any reference to this on Novell's support website. In fact, as referenced above, Novell's own documentation [TID# 10011973 - last updated on June 29, 2000] does not address this issue. In that document, they answer the question, "How do I create an admin for a container that cuts off the main admin?" They do not specify the filtering of Selected Properties Rights, and thus leave readers open to this vulnerability. Safe Computing, -FogHorn Security Staff
Current thread:
- Bypassing Inherited Rights Filters in Novell Directory Services. FogHorn Security (Sep 07)
- Re: Bypassing Inherited Rights Filters in Novell Directory Services. Bob Fiero (Sep 12)