The following analytic identifies suspicious PowerShell script execution via EventCode 4104 that is using the
mutex function. This function is commonly seen in some obfuscated PowerShell scripts to make sure that only one instance of there process is running on a compromise machine. During triage, review parallel processes within the same timeframe. Review the full script block to identify other related artifacts.
- Type: TTP
Product: Splunk Enterprise, Splunk Enterprise Security, Splunk Cloud
- Last Updated: 2022-05-02
- Author: Teoderick Contreras, Splunk
- ID: 637557ec-ca08-11eb-bd0a-acde48001122
Kill Chain Phase
1 2 3 4 5 `powershell` EventCode=4104 ScriptBlockText = "*Threading.Mutex*" | stats count min(_time) as firstTime max(_time) as lastTime by EventCode ScriptBlockText Computer UserID | `security_content_ctime(firstTime)` | `security_content_ctime(lastTime)` | `powershell_creating_thread_mutex_filter`
The SPL above uses the following Macros:
powershell_creating_thread_mutex_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/184.108.40.206/GetDataIn/AddPowerShell#Configure_module_logging_for_PowerShell.
Known False Positives
powershell developer may used this function in their script for instance checking too.
Associated Analytic Story
|40.0||50||80||A suspicious powershell script contains Thread Mutex in $ScriptBlockText$ with EventCode $EventCode$ in host $Computer$|
The Risk Score is calculated by the following formula: Risk Score = (Impact * Confidence/100). Initial Confidence and Impact is set by the analytic author.
source | version: 3