Command Line
at.exe at 09:00 /interactive /every:m,t,w,th,f,s,su C:\Windows\System32\revshell.exe
Description
Create a recurring scheduled task which will trigger every day at 9 AM, launching the target executable - often abused by cyber threats to achieve persistence in scheduled task format.
Risk
Medium
Risk Reason
AT is typically not used in a normal user capacity and will only be utilized by system administrators or IT operators - seeing an executable triggered for regular execution should be investigated to determine the legitimacy.
Fidelity
Medium
Fidelity Reason
AT or similar utilities are often invoked automatically during software deployments, updates, etc - as such, this type of alerting cannot often be used as a critical.
Operating Systems
Killchain Phases
References
MITRE ATT&CK TECHNIQUES
URL: https://attack.mitre.org/techniques/T1053/002
Description: Adversaries may abuse the [at](https://attack.mitre.org/software/S0110) utility to perform task scheduling for initial or recurring execution of malicious code. The [at](https://attack.mitre.org/software/S0110) utility exists as an executable within Windows, Linux, and macOS for scheduling tasks at a specified time and date. Although deprecated in favor of [Scheduled Task](https://attack.mitre.org/techniques/T1053/005)'s [schtasks](https://attack.mitre.org/software/S0111) in Windows environments, using [at](https://attack.mitre.org/software/S0110) requires that the Task Scheduler service be running, and the user to be logged on as a member of the local Administrators group.
On Linux and macOS, [at](https://attack.mitre.org/software/S0110) may be invoked by the superuser as well as any users added to the at.allow file. If the at.allow file does not exist, the at.deny file is checked. Every username not listed in at.deny is allowed to invoke [at](https://attack.mitre.org/software/S0110). If the at.deny exists and is empty, global use of [at](https://attack.mitre.org/software/S0110) is permitted. If neither file exists (which is often the baseline) only the superuser is allowed to use [at](https://attack.mitre.org/software/S0110).(Citation: Linux at)
Adversaries may use [at](https://attack.mitre.org/software/S0110) to execute programs at system startup or on a scheduled basis for [Persistence](https://attack.mitre.org/tactics/TA0003). [at](https://attack.mitre.org/software/S0110) can also be abused to conduct remote [Execution](https://attack.mitre.org/tactics/TA0002) as part of [Lateral Movement](https://attack.mitre.org/tactics/TA0008) and/or to run a process under the context of a specified account (such as SYSTEM).
In Linux environments, adversaries may also abuse [at](https://attack.mitre.org/software/S0110) to break out of restricted environments by using a task to spawn an interactive system shell or to run system commands. Similarly, [at](https://attack.mitre.org/software/S0110) may also be used for [Privilege Escalation](https://attack.mitre.org/tactics/TA0004) if the binary is allowed to run as superuser via sudo.(Citation: GTFObins at)
Tactics:
- Execution
- Persistence
- Privilege Escalation