Windows Exfiltration Over C2 Via Powershell UploadString
The following analytic identifies potential data exfiltration using the PowerShell net.webclient command. This technique was observed in the Winter-Vivern malware, which uploads desktop screenshots and files from compromised or targeted hosts. Detecting this TTP can serve as a valuable indicator that a process is attempting to upload files to an external or internal URI link. We recommend examining the process, the files it is trying to upload, and the URL link or C2 destination where the data is being uploaded.
- Type: TTP
Product: Splunk Enterprise, Splunk Enterprise Security, Splunk Cloud
- Last Updated: 2023-04-05
- Author: Teoderick Contreras, Splunk
- ID: 59e8bf41-7472-412a-90d3-00f3afa452e9
Kill Chain Phase
- Actions On Objectives
- CIS 10
1 2 3 4 5 `powershell` EventCode=4104 ScriptBlockText = "*Net.webclient*" AND ScriptBlockText = "*.UploadString*" | stats count min(_time) as firstTime max(_time) as lastTime by EventCode ScriptBlockText Computer UserID | `security_content_ctime(firstTime)` | `security_content_ctime(lastTime)` | `windows_exfiltration_over_c2_via_powershell_uploadstring_filter`
The SPL above uses the following Macros:
windows_exfiltration_over_c2_via_powershell_uploadstring_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
False positives should be limited. Filter as needed.
Associated Analytic Story
|49.0||70||70||A PowerShell script on $Computer$ is attempting to transfer files to a remote URL.|
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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