![]() If you’re aware that AppLocker supports exceptions, you may have this thought. Unseasoned AppLocker users often go for this approach, which can burn quite badly. Let’s give you some examples of incorrect ways that people attack it. The requirement sounds easy enough, but AppLocker can be a little bit tricky to get right with these parameters. Obviously it goes without saying that you’d need to turn on AppLocker (by enabling the App Identity service and configuring it for “Enforced” – both of which are covered in the article linked above) and create your required AD group ahead of time. Let’s take an example and use FTP – the FTP executable is only to be used by Administrators, and any users added to an “FTP Allow” Active Directory group. The commonest use case I see is that people want administrators to be able to run anything, but wish to restrict the use of certain system executables to “whitelist” groups. There are GPOs that can control some of these, but if AppLocker is your approach then it makes sense to leverage that. Think anything in the Windows system folders – the command prompt, Registry editor, FTP, subst, etc., etc. Rather than discuss the ins and outs of each of these technology stacks (or even third-party tools that can extend these capabilities, such as Ivanti Application Control or Citrix WEM), I will simply link you to this article for further reading (which was actually written by me, despite what the author details may have you think!)Ī common requirement for any application management tool is to restrict system applications. It superseded the old Software Restriction Policies and is itself slated to be replaced by Microsoft Defender Application Control, but as of today, it is still the recommended application management solution, particularly within multi-user environments. As AppLocker by default trusts Microsoft signed binaries and Windows folders it is essential to evaluate permissions and trusted binaries that can execute code in order to protect effectively the Windows ecosystem.I have been asked about this a few times in the past, so thought I would quickly document it while it is fresh in my memory.ĪppLocker is Microsoft’s GPO-based technology that deals with application execution restriction. Implementing AppLocker by default doesn’t really provide any security measure since it can be bypassed easily. AppLocker – Default Rules AppLocker Bypass – Weak Path Rules Conclusion Otherwise it will be blocked by the AppLocker rules. Since the AppLocker rules are allowing files that are contained inside the Windows folder to be executed then the utility would run as normal. AppLocker – Binary Planting into Weak Folder In this case the executable is the legitimate application accesschk64. ![]() The next step is to drop the binary into the folder that has weak permissions and execute it. The accesschk tool can be used to identify if the group “Users” have RW permissions inside the Windows folder. Windows environments (check was done in Windows Server 2008 R2) by default allowing standard users of the system to have read and write access in these folders: ![]() ![]() AppLocker rules by default are allowing all the files that are inside in the Windows folder and Program files to be executed as otherwise the system will not operate as normal. If appropriate permissions are not set in these folders an attacker could exploit this in order to bypass AppLocker.
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