This analytic identifies suspicious modification of ACL permission to a files or folder to make it available to everyone or to a specific user. This technique may be used by the adversary to evade ACLs or protected files access. This changes is commonly configured by the file or directory owner with appropriate permission. This behavior raises suspicion if this command is seen on an endpoint utilized by an account with no permission to do so.
- Type: Anomaly
- Product: Splunk Behavioral Analytics
- Datamodel: Endpoint_Processes
- Last Updated: 2022-03-17
- Author: Teoderick Contreras, Splunk
- ID: 9ae9a48a-cdbe-11eb-875a-acde48001122
Kill Chain Phase
- CIS 8
- CIS 13
1 2 3 4 5 6 7 8 | from read_ssa_enriched_events() | eval timestamp=parse_long(ucast(map_get(input_event, "_time"), "string", null)), process=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 process IS NOT NULL AND NOT like(process, "%:\\Windows\\QG\\ServiceNow%") AND like(process, "%/g%") | where (match_regex(process, /(?i)everyone:/)=true OR match_regex(process, /(?i)SYSTEM:/)=true OR match_regex(process, /(?i)S-1-1-0:/)=true) | where (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, "process", process, "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:
modify_acls_permission_of_files_or_folders_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 cacls.exe may be used.
Known False Positives
System administrators may use this windows utility. filter is needed.
Associated Analytic Story
|35.0||50||70||A cacls process $process_name$ with commandline $cmd_line$ try to modify 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