The following analytic identifies Aspnet_Compiler.exe which is a native living off the land binary or script (LOLBAS) within the Windows operating system that may be abused by adversaries by moving it to a new directory. The list of binaries was derived from the https://lolbas-project.github.io site.
- Type: Anomaly
- Product: Splunk Behavioral Analytics
- Datamodel: Endpoint_Processes
- Last Updated: 2022-10-18
- Author: Splunk Threat Research Bot, Splunk
- ID: d75cc561-3828-4d0a-92c4-0eb93bfe0929
Kill Chain Phase
- Actions on Objectives
- CIS 8
1 2 3 4 5 6 7 | from read_ssa_enriched_events() | eval device=ucast(map_get(input_event, "dest_device_id"), "string", null), user=ucast(map_get(input_event, "dest_user_id"), "string", null), timestamp=parse_long(ucast(map_get(input_event, "_time"), "string", null)), process_name=lower(ucast(map_get(input_event, "process_name"), "string", null)), process_path=lower(ucast(map_get(input_event, "process_path"), "string", null)), event_id=ucast(map_get(input_event, "event_id"), "string", null) | where process_name IS NOT NULL AND process_name="aspnet_compiler.exe" | where process_path IS NOT NULL AND match_regex(process_path, /(?i)\\windows\\microsoft.net\\framework64\\v4.0.30319/)=false | eval start_time=timestamp,end_time=timestamp, entities=mvappend(device, user), body=create_map(["event_id", event_id, "process_path", process_path, "process_name", process_name]) | into write_ssa_detected_events();
The SPL above uses the following Macros:
windows_rename_system_utilities_aspnet_compiler_exe_lolbas_in_non_standard_path_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 must be ingesting logs with the process name, command-line arguments, and parent processes from your endpoints. Collect endpoint data such as Sysmon or Windows Events 4688.
Known False Positives
False positives may be present and filtering may be required. Certain utilities will run from non-standard paths based on the third-party application in use.
Associated Analytic Story
|14.0||20||70||A system process $process_name$ with path $process_path$ spawn in non-default folder path on 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.
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