This analytic identifies a common fileless malware staging technique of using .NET classes to directly download a URL payload into memory. The analytic utilizes PowerShell Script Block Logging (EventCode=4104) to identify suspicious PowerShell execution.
- Type: TTP
Product: Splunk Enterprise, Splunk Enterprise Security, Splunk Cloud
- Last Updated: 2023-06-13
- Author: Steven Dick
- ID: 103affa6-924a-4b53-aff4-1d5075342aab
Kill Chain Phase
- Command and Control
- CIS 10
1 2 3 4 5 6 7 `powershell` EventCode=4104 ScriptBlockText IN ("*system.net.webclient*","*system.net.webrequest*") AND ScriptBlockText="*IO.MemoryStream*" | eval Path = case(isnotnull(Path),Path,true(),"unknown") | stats count min(_time) as firstTime max(_time) as lastTime list(ScriptBlockText) as command values(Path) as file_name values(UserID) as user by ActivityID, Computer, EventCode | rename Computer as dest, EventCode as signature_id | `security_content_ctime(firstTime)` | `security_content_ctime(lastTime)` | `powershell_webrequest_using_memory_stream_filter`
The SPL above uses the following Macros:
powershell_webrequest_using_memory_stream_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
The following analytic requires PowerShell operational logs to be imported. Modify the powershell macro as needed to match the sourcetype or add index. This analytic is specific to 4104, or PowerShell Script Block Logging.
Known False Positives
Unknown, possible custom scripting.
Associated Analytic Story
|80.0||100||80||Powershell webrequest to memory stream behavior. Possible fileless malware staging on $dest$ by $user$.|
The Risk Score is calculated by the following formula: Risk Score = (Impact * Confidence/100). Initial Confidence and Impact is set by the analytic author.
source | version: 1