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 no critical endpoints or all.
This analytic identifies
GetProcAddress in the script block. This is not normal to be used by most PowerShell scripts and is typically unsafe/malicious. Many attack toolkits use GetProcAddress to obtain code execution.
$var_gpa = $var_unsafe_native_methods.GetMethod(GetProcAddress and later referenced/executed elsewhere.
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: 2023-04-14
- Author: Michael Haag, Splunk
- ID: a26d9db4-c883-11eb-9d75-acde48001122
Kill Chain Phase
- CIS 10
1 2 3 4 5 `powershell` EventCode=4104 ScriptBlockText=*getprocaddress* | stats count min(_time) as firstTime max(_time) as lastTime by Opcode Computer UserID EventCode ScriptBlockText | `security_content_ctime(firstTime)` | `security_content_ctime(lastTime)` | `powershell_fileless_process_injection_via_getprocaddress_filter`
The SPL above uses the following Macros:
powershell_fileless_process_injection_via_getprocaddress_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. Filter as needed.
Associated Analytic Story
|48.0||60||80||A suspicious powershell script contains GetProcAddress API 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: 2