The following analytic identifies the use of
xcacls.exe placing the deny permission on a file or directory. Adversaries perform this behavior to prevent responders from reviewing or gaining access to adversary files on disk.
- Type: TTP
- Product: Splunk Behavioral Analytics
- Datamodel: Endpoint_Processes
- Last Updated: 2021-11-29
- Author: Teoderick Contreras, Splunk
- ID: b76eae28-cd25-11eb-9c92-acde48001122
Kill Chain Phase
- CIS 14
- CIS 16
1 2 3 4 5 6 | from read_ssa_enriched_events() | eval timestamp=parse_long(ucast(map_get(input_event, "_time"), "string", null)), cmd_line=ucast(map_get(input_event, "process"), "string", null), process_name=ucast(map_get(input_event, "process_name"), "string", null), process_path=ucast(map_get(input_event, "process_path"), "string", null), parent_process_name=ucast(map_get(input_event, "parent_process_name"), "string", null), event_id=ucast(map_get(input_event, "event_id"), "string", null) | where cmd_line IS NOT NULL AND match_regex(cmd_line, /(?i)deny/)=true AND (process_name="cacls.exe" OR process_name="xcacls.exe" OR process_name="icacls.exe") | eval start_time=timestamp, end_time=timestamp, entities=mvappend(ucast(map_get(input_event, "dest_user_id"), "string", null), ucast(map_get(input_event, "dest_device_id"), "string", null)), body=create_map(["event_id", event_id, "cmd_line", cmd_line, "process_name", process_name, "parent_process_name", parent_process_name, "process_path", process_path]) | into write_ssa_detected_events();
The SPL above uses the following Macros:
deny_permission_using_cacls_utility_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 logs with the process name, parent process, and command-line executions from your endpoints. If you are using Sysmon, you must have at least version 6.0.4 of the Sysmon TA. Tune and filter known instances where renamed icacls.exe may be used.
Known False Positives
System administrators may use cacls utilities but this is not a common practice. Filter as needed.
Associated Analytic Story
|35.0||50||70||A cacls process $process_name$ with commandline $cmd_line$ try to deny a permission of a file or directory in host $dest_device_id$|
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