Microsoft applocker2/21/2023 ![]() Most IT endpoints are not static, causing this AppLocker configuration to be difficult to manage at scale. For static environments, this is a great option, as causing a hash collision is incredibly difficult. While daunting at first, it’s easy to use PowerShell scripts to scan a reference system, format an AppLocker XML policy and import directly into the endpoint’s AppLocker configuration. This also has the benefit of preventing unwanted software from running on the endpoint, be it in a known or unknown location. The next option is to import a list of known hashes into AppLocker and block anything else from running. However, for a malicious attacker, simply placing the malware in a “known” location can bypass the AppLocker’s intended function. This prevents mainly unwanted software from running, as it would be installed in an “unknown” location on the operating system.Īdditionally, this is the easiest to maintain, as expected locations for applications to execute from will maintain fairly static. Using the golden image as a reference system, the expected Windows and installed applications can be profiled and imported into AppLocker relatively easily. Stating which paths can execute on a file system is the easiest step for an organization to lock down an endpoint. Each of these has their pros and cons, which I will discuss here. To make this decision on what is able to execute, AppLocker can inspect the file’s path, hash, or publisher information. For many organizations, this is a great technology to reduce the attack surface of the endpoint by limiting what can run to a specific set of known files. It provides the ability to lock down installers, scripts and executables on the local machine via either a white list or a black list of file data. Please leave any feedback you have as a comment to this post.Windows AppLocker is a powerful whitelisting technology built into modern Windows operating systems. Do a code audit of the script if you run it in a sensitive environment. I am not responsible for what this script does. You will see some errors when the script could copy a file, but not execute it:Īt the end you should see something like this (in this case it was run on a Windows 10 build 10565):ĭon’t forget you might need to validate all the Program Files subfolders in a similar fashion if you keep that Default Rule. I did notice that I got these warnings when bypassing Execution Policy (but not when changing the Execution Policy to RemoteSigned). Here are 13 additional ways to bypass it: It is meant to prevent accidental execution of scripts. This is also a good reminder that Execution Policy is NOT a security feature. Run Powershell with the option “-ExecutionPolicy Bypass”:.Open the script in Windows PowerShell ISE (by right-clicking the script and choosing Edit), select the entire script with Crtl-A and then press F8 to run the selected code.In that case you have (at least) two simple options: You might have an Execution Policy that prevents you from running the script. And if you wanted to bypass AppLocker as an admin (in case the default Admin Rule was removed) you could just stop the service “Application Identity” that AppLocker relies on to function properly. ![]() Admins have another Default Rule that enables them to run anything anywhere. They will be closed automatically by the script. During the test you will see instances of this showing up:ĭo not close them manually, as they are enumerated by the script at the end. ![]() I chose mstsc.exe as the executable (it’s short for Microsoft Terminal Services Client), since it is small, built-in and can run multiple instances. I would not recommend messing with the NTFS permissions on folders in C:\Windows (or where your %systemroot% is located). Preferably by creating exceptions in the default Allow Rule or by adding a new Deny Rule that includes these folders. At the end it will show what folders are at risk for AppLocker bypass and must be managed accordingly. ![]() I wrote a PowerShell script that tries to copy an executable to every folder in Windows and (if the copy succeeds) tries to execute it. But as it turns out that is not the case. The reasoning behind this must have been that a non-admin Windows-user should not have write permissions anywhere in that folder. One of the Default Rules in AppLocker allows everyone to execute everything in the folder C:\Windows: ![]()
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