On 9/11/19 10:56 AM, Emil Petersson wrote:

Even when I reconfigure AD to make sure there is no applicable GPO's found, I'm still granted access with my unprivileged user.

[ad_gpo_access_check] (0x0400): RESULTANT POLICY: [ad_gpo_access_check] (0x0400): gpo_map_type: Remote Interactive [ad_gpo_access_check] (0x0400): allowed_size = 0 [ad_gpo_access_check] (0x0400): denied_size = 0 ...snip... [ad_gpo_access_check] (0x0400): CURRENT USER: [ad_gpo_access_check] (0x0400): user_sid = S-1-5-21-1107582786-xxx-2594897426-2570 [ad_gpo_access_check] (0x0400): group_sids[0] = S-1-5-21-1107582786-xxx-2594897426-513 [ad_gpo_access_check] (0x0400): group_sids[1] = S-1-5-11 [ad_gpo_access_check] (0x0400): POLICY DECISION: [ad_gpo_access_check] (0x0400): access_granted = 1 [ad_gpo_access_check] (0x0400): access_denied = 0 [ad_gpo_access_done] (0x0400): GPO-based access control successful.

In this case, shouldn't the new feature "ad_gpo_implicit_deny" kick in and make sure the user is denied?

Hi,

you are correct.

It should deny access to the user. Both this log and the log from your previous email look like there is some issue with SSSD. I will try to reproduce it locally, but from the logs you provided it looks like a bug.

Michal

On 10/3/19 10:28 AM, Emil Petersson wrote:

Hi,

The docs for ad_gpo_implicit_deny reads:

"Normally when no applicable GPOs are found the users are allowed access. When this option is set to True users will be allowed access only when explicitly allowed by a GPO rule. Otherwise users will be denied access. This can be used to harden security but be careful when using this option because it can deny access even to users in the built-in Administrators group if no GPO rules apply to them."

In my case, there are GPOs found, it's just that none of them touches RemoteInteractiveLogonRight or DenyRemoteInteractiveLogonRight.

Does ad_gpo_implicit_deny work in such a way that it's only effective when no (0) GPOs are found? That might explain the behaviour I'm seeing. If this is the case, I suggest that ad_gpo_implicit_deny should be effective also when none of the detected GPOs explicitly allows or denies remote logon.

Sorry, I missed your response.

You are right the ad_gpo_implicit_deny only works when there is not policy found on the server that applies to the user (0 GPOs applicable).

If there is a GPO that is applicable, but does not contain any access control rules then the ad_gpo_implicit_deny does not kick in.

I completely missread the logs you send before. I gave the feature a smoke test and it worked for me.

Michal

On 10/10/19 11:43 AM, Emil Petersson wrote:

Ok, thanks, that explains it.

All I want is a way to make sure that a user, which I have not explicitly allowed access, is denied. In other words... default behaviour for all logins should always be DENY, regardless of number of GPOs found. Obviously, a GPO that does contain access control rules should override this default behavior.

Right now we are forced to fall back to either "access_provider=simple" or "ad_access_filter" just to make sure that the default behavior for logins are DENY, which unfortunately defeats the whole idea of using GPO for access control.

Any advice on how to achieve my desired functionality is appreciated.

Thanks!

Currently your only way is to actually define the GPO on the AD server. I would probably put it to a separate GPO, something like access_control_gpo and define these rules there:

Allow log on locally Allow log on through remote desktop sevices Allow log on as a service Allow log on as a batch job Access this computer from the network

Define these rules and put Administrators group to all of them. Then you can add whatever user/group you want to login (you are probably mostly interested in the Allow log on locally and Allow log on through remote desktop services if you are using default PAM to GPO rule mapping, but it is still better to define all these rules explicitly if you really want a complete whitelist on the server).

Or alternatively make all GPOs on the server not applicable to the SSSD host (but I agree that this is kind of clumsy solution if you have many GPOs, so it is better to go with the above and define the policies).

Regarding SSSD side options. Maybe we should add a stronger mode for ad_gpo_implicit_deny to "only allow explicitly allowed" users/groups not only deny access if there are no applicable GPOs. I think such option would be good hardening option, but it would basically ignore all Deny rules on the server (OTOH if someone wants to allow only whitelisted users/groups they would not use deny rules, so that is actually not a problem). Will you file an RFE or should I? Feel free to copy paste this discussion to the ticket.

Michal