The following analytic utilizes PowerShell Script Block Logging (EventCode=4104) to identify suspicious PowerShell execution. Script Block Logging captures the command sent to PowerShell, the full command to be executed. Upon enabling, logs will output to Windows event logs. Dependent upon volume, enable on critical endpoints or all.
This analytic identifies
[System.IO.File]::Copy being used to capture the SAM, SYSTEM or SECURITY hives identified in script block. This will catch the most basic use cases for credentials being taken for offline cracking.
During triage, review parallel processes using an EDR product or 4688 events. It will be important to understand the timeline of events around this activity. Review the entire logged PowerShell script block.
- Type: TTP
Product: Splunk Enterprise, Splunk Enterprise Security, Splunk Cloud
- Last Updated: 2021-07-21
- Author: Michael Haag, Splunk
- ID: 9251299c-ea5b-11eb-a8de-acde48001122
Kill Chain Phase
1 2 3 4 5 `powershell` EventCode=4104 Message IN ("*copy*","*[System.IO.File]::Copy*") AND Message IN ("*System32\\config\\SAM*", "*System32\\config\\SYSTEM*","*System32\\config\\SECURITY*") | stats count min(_time) as firstTime max(_time) as lastTime by OpCode ComputerName User EventCode Message | `security_content_ctime(firstTime)` | `security_content_ctime(lastTime)` | `detect_copy_of_shadowcopy_with_script_block_logging_filter`
The SPL above uses the following Macros:
detect_copy_of_shadowcopy_with_script_block_logging_filter is a empty macro by default. It allows the user to filter out any results (false positives) without editing the SPL.
List of fields required to use this analytic.
How To Implement
To successfully implement this analytic, you will need to enable PowerShell Script Block Logging on some or all endpoints. Additional setup here https://docs.splunk.com/Documentation/UBA/220.127.116.11/GetDataIn/AddPowerShell#Configure_module_logging_for_PowerShell.
Known False Positives
Limited false positives as the scope is limited to SAM, SYSTEM and SECURITY hives.
Associated Analytic Story
|80.0||80||100||PowerShell was identified running a script to capture the SAM hive on endpoint $ComputerName$ by user $user$.|
The Risk Score is calculated by the following formula: Risk Score = (Impact * Confidence/100). Initial Confidence and Impact is set by the analytic author.
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