this analytic is to detect a suspicious compile before delivery approach of .net compiler csc.exe. This technique was seen in several adversaries, malware and even in red teams to take advantage the csc.exe .net compiler tool to compile on the fly a malicious .net code to evade detection from security product. This is a good hunting query to check further the file or process created after this event and check the file path that passed to csc.exe which is the .net code. Aside from that, powershell is capable of using this compiler in executing .net code in a powershell script so filter on that case is needed.
- Type: Hunting
- Product: Splunk Enterprise, Splunk Enterprise Security, Splunk Cloud
- Datamodel: Endpoint
- Last Updated: 2021-11-12
- Author: Teoderick Contreras, Splunk
- ID: ea73128a-43ab-11ec-9753-acde48001122
Kill Chain Phase
- CIS 10
1 2 3 4 5 6 | tstats `security_content_summariesonly` count min(_time) as firstTime max(_time) as lastTime from datamodel=Endpoint.Processes where `process_csc` Processes.process = "*/noconfig*" Processes.process = "*/fullpaths*" Processes.process = "*@*" by Processes.dest Processes.user Processes.parent_process_name Processes.parent_process Processes.process_name Processes.process Processes.process_id Processes.parent_process_id | `drop_dm_object_name(Processes)` | `security_content_ctime(firstTime)` | `security_content_ctime(lastTime)` | `csc_net_on_the_fly_compilation_filter`
The SPL above uses the following Macros:
csc_net_on_the_fly_compilation_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
The detection is based on data that originates from Endpoint Detection and Response (EDR) agents. These agents are designed to provide security-related telemetry from the endpoints where the agent is installed. To implement this search, you must ingest logs that contain the process GUID, process name, and parent process. Additionally, you must ingest complete command-line executions. These logs must be processed using the appropriate Splunk Technology Add-ons that are specific to the EDR product. The logs must also be mapped to the
Processes node of the
Endpoint data model. Use the Splunk Common Information Model (CIM) to normalize the field names and speed up the data modeling process.
Known False Positives
A network operator or systems administrator may utilize an automated powershell script taht execute .net code that may generate false positive. filter is needed.
Associated Analytic Story
|25.0||50||50||csc.exe with commandline $process$ to compile .net code on $dest$ by $user$|
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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