This analytic is developed to identify suspicious file creation in the root drive (C:). This tactic was observed in NjRAT as a means to ascertain whether its malware instance running on the compromised host possesses administrative privileges. The methodology involves an attempt to create a 'win.dat' file in the C:\ directory. If this file is successfully created, it serves as an indicator that the process indeed holds administrative privileges. This anomaly detection mechanism serves as a valuable pivot point for detecting NjRAT and other malware strains employing similar techniques to assess the privileges of their running malware instances, without using token privilege API calls or PowerShell commandlets.
- Type: Anomaly
- Product: Splunk Enterprise, Splunk Enterprise Security, Splunk Cloud
- Datamodel: Endpoint
- Last Updated: 2023-09-19
- Author: Teoderick Contreras, Splunk
- ID: e08620cb-9488-4052-832d-97bcc0afd414
Kill Chain Phase
- CIS 10
1 2 3 4 5 6 7 8 9 10 |tstats `security_content_summariesonly` count min(_time) as firstTime max(_time) as lastTime from datamodel=Endpoint.Filesystem where Filesystem.file_name IN ("*.exe", "*.dll", "*.sys", "*.com", "*.vbs", "*.vbe", "*.js", "*.bat", "*.cmd", "*.pif", "*.lnk", "*.dat") by Filesystem.dest Filesystem.file_create_time Filesystem.process_id Filesystem.process_guid Filesystem.file_name Filesystem.file_path Filesystem.user | `drop_dm_object_name(Filesystem)` | eval dropped_file_path = split(file_path, "\\") | eval dropped_file_path_split_count = mvcount(dropped_file_path) | eval root_drive = mvindex(dropped_file_path,0) | where LIKE(root_drive, "C:") AND dropped_file_path_split_count = 2 | `security_content_ctime(firstTime)` | `security_content_ctime(lastTime)` | `windows_admin_permission_discovery_filter`
The SPL above uses the following Macros:
windows_admin_permission_discovery_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 search you need to be ingesting information on process that include the name of the Filesystem responsible for the changes from your endpoints into the
Endpoint datamodel in the
Known False Positives
False positives may occur if there are legitimate accounts with the privilege to drop files in the root of the C drive. It's recommended to verify the legitimacy of such actions and the accounts involved.
Associated Analytic Story
|25.0||50||50||A file was created in root drive C:/ on host - $dest$|
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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