The answer is: manual enumeration and using tools to piece together findings that hint to a scheduled task running.Īlthough this is not perfect, it can be quite effective. So the real question is: how can we find a scheduled task if there is no way to query any interesting ones as a standard user? Let’s try the top Get-ScheduledTask command again, but this time as a standard user.Īs expected and mentioned earlier, this search does NOT show the custom task that are created by other users… From here we could take the name of the task we are interested in and get all of the info about that specific task with the schtasks command.īut what is the point of this if we cannot see it from our standard user? - Good question! The PowerShell search only provides three fields of information however the output is cleaner and easy to spot outliers. We can accomplish the same search using PowerShell and the following command: Get-ScheduledTask This is common for custom tasks as it is not required to add the actual folder and this is default so it often gets left as-is. Additionally, scheduled tasks are listed in order by folder, which in this case has been set with a root folder ( \ ). It’s custom and therefor “newer” than the others. Note that this task was right on top because of two reasons. Additionally we can see that the task runs every five minutes and executes as SYSTEM. This provides us with a lot of good information about the task. This means that any tasks we are interested in, such as those created by the administrator, we will not see when trying to query for them.įor example, if we use the following command with administrative permissions, we can query the scheduled task to find information about how it works: schtasks /query /fo LIST /v | findstr /B /C:"Folder" /C:"TaskName" /C:"Run As User" /C:"Schedule" /C:"Scheduled Task State" /C:"Schedule Type" /C:"Repeat: Every" /C:"Comment" Unfortunately for us as the attacker, Microsoft does something pretty smart and only allows standard users to view scheduled tasks that belong to them. Hunting for Scheduled Tasksīefore we dive into the enumeration of scheduled tasks, we need to understand our visibility as a standard user. Once we have put all the pieces together, we will replace the scheduled task’s actual binary with our own malicious binary that will provide us with a reverse shell as SYSTEM.Īdditionally, we will review a CVE related to scheduled tasks that affects all Windows versions up to and including Windusing Metasploit. After that, we will enumerate the permissions on the folder where the scheduled task is running out of, which will reveal that standard users have modify permissions. From there we will enumerate the scheduled tasks running on the system and confirm our suspicion about our findings. We will start by performing some basic manual enumeration to find what appears to be a scheduled task that is running. Specifically, we will be targeting a folder where a scheduled task is executing from and that also allows a standard user to write in. Similar to many of the Windows privilege escalation techniques we have gone over in other posts, this one has to do with weak folder permissions as well. Want to stay up to date with the latest hacks?įor this post on Windows Privilege Escalation techniques, we will be exploring vulnerable scheduled tasks.CVE-2018-8440 – A Scheduled Task Kernel Exploit.Additional Considerations when Hunting Scheduled Tasks.Exploiting a Scheduled Task to get a SYSTEM Shell.Enumerating Folder Permissions – Accesschk.Enumerating Folder Permissions – icacls.Basic Enumeration Leads to Interesting Finding.Of course, I can change setting for each task in the list, but I don't want to set up every new task manually, and check all the time if an application restores a task settings back. For example, if my computer returns from hibernation, do all the missed tasks run at once or not? If yes, I'd like to set up the scheduler to run scheduled tasks one at a time. Is it true that on Windows 10 a number of scheduled tasks may run simultaneously? If yes, how can I set up the scheduler to run scheduled tasks one at a time?ĮDIT: The point is most of tasks has "Run task as soon as possible after a scheduled start is missed" enabled. But I would like to regularize tasks run somehow. Moreover, I don't like an idea that I have to search and remove a tasks for every installed application. I tried to remove some tasks from the scheduler, but applications create them again. One day, it looks like all the tasks start at once, and I have to wait quite a long time for the computer resources to be released. Every single application considers it its duty to create at least a task to run an updater. The task scheduler in my Windows 10 has a number of scheduled tasks created by applications.
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