Detection: Windows Scheduled Task DLL Module Loaded

Updated Date: 2024-09-30 ID: bc5b2304-f241-419b-874a-e927f667b7b6 Author: Teoderick Contreras, Splunk Type: TTP Product: Splunk Enterprise Security

Description

The following analytic detects instances where the taskschd.dll is loaded by processes running in suspicious or writable directories. This activity is unusual, as legitimate processes that load taskschd.dll typically reside in protected system locations. Malware or threat actors may attempt to load this DLL from writable or non-standard directories to manipulate the Task Scheduler and execute malicious tasks. By identifying processes that load taskschd.dll in these unsafe locations, this detection helps security analysts flag potentially malicious activity and investigate further to prevent unauthorized system modifications.

1`sysmon` EventCode=7 Image IN ("*\\windows\\fonts\\*", "*\\windows\\temp\\*", "*\\users\\public\\*", "*\\windows\\debug\\*", "*\\Users\\Administrator\\Music\\*", "*\\Windows\\servicing\\*", "*\\Users\\Default\\*", "*Recycle.bin*", "*\\Windows\\Media\\*", "\\Windows\\repair\\*", "*\\temp\\*", "*\\PerfLogs\\*") ImageLoaded = "*\\taskschd.dll" 
2| stats min(_time) as firstTime max(_time) as lastTime count by user_id, dest, Image ,ImageLoaded, , OriginalFileName, ProcessGuid 
3| `security_content_ctime(firstTime)` 
4| `security_content_ctime(lastTime)` 
5| `windows_scheduled_task_dll_module_loaded_filter`

Data Source

Name Platform Sourcetype Source
Sysmon EventID 7 Windows icon Windows 'xmlwineventlog' 'XmlWinEventLog:Microsoft-Windows-Sysmon/Operational'

Macros Used

Name Value
security_content_ctime convert timeformat="%Y-%m-%dT%H:%M:%S" ctime($field$)
windows_scheduled_task_dll_module_loaded_filter search *
windows_scheduled_task_dll_module_loaded_filter is an empty macro by default. It allows the user to filter out any results (false positives) without editing the SPL.

Annotations

- MITRE ATT&CK
+ Kill Chain Phases
+ NIST
+ CIS
- Threat Actors
ID Technique Tactic
T1053 Scheduled Task/Job Execution
KillChainPhase.EXPLOITAITON
KillChainPhase.INSTALLATION
NistCategory.DE_CM
Cis18Value.CIS_10
Earth Lusca

Default Configuration

This detection is configured by default in Splunk Enterprise Security to run with the following settings:

Setting Value
Disabled true
Cron Schedule 0 * * * *
Earliest Time -70m@m
Latest Time -10m@m
Schedule Window auto
Creates Notable Yes
Rule Title %name%
Rule Description %description%
Notable Event Fields user, dest
Creates Risk Event True
This configuration file applies to all detections of type TTP. These detections will use Risk Based Alerting and generate Notable Events.

Implementation

To successfully implement this search, you need to be ingesting logs with the process name and imageloaded executions from your endpoints. If you are using Sysmon, you must have at least version 6.0.4 of the Sysmon TA.

Known False Positives

Third party Legitimate application may load this task schedule dll module.

Associated Analytic Story

Risk Based Analytics (RBA)

Risk Message Risk Score Impact Confidence
A taskschd.dll was loaded by a process - [$Image$] on [$dest$] 64 80 80
The Risk Score is calculated by the following formula: Risk Score = (Impact * Confidence/100). Initial Confidence and Impact is set by the analytic author.

References

Detection Testing

Test Type Status Dataset Source Sourcetype
Validation ✅ Passing N/A N/A N/A
Unit ✅ Passing Dataset XmlWinEventLog:Microsoft-Windows-Sysmon/Operational XmlWinEventLog
Integration ✅ Passing Dataset XmlWinEventLog:Microsoft-Windows-Sysmon/Operational XmlWinEventLog

Replay any dataset to Splunk Enterprise by using our replay.py tool or the UI. Alternatively you can replay a dataset into a Splunk Attack Range

Source: GitHub | Version: 3