Detection: Batch File Write to System32

Description

The following analytic detects the creation of a batch file (.bat) within the Windows system directory tree, specifically in the System32 or SysWOW64 folders. It leverages data from the Endpoint datamodel, focusing on process and filesystem events to identify this behavior. This activity is significant because writing batch files to system directories can be indicative of malicious intent, such as persistence mechanisms or system manipulation. If confirmed malicious, this could allow an attacker to execute arbitrary commands with elevated privileges, potentially compromising the entire system.

Search

 1
 2| tstats `security_content_summariesonly` count FROM datamodel=Endpoint.Processes where Processes.process_name=* by _time span=1h Processes.process_guid Processes.process_name Processes.dest Processes.user 
 3| `drop_dm_object_name(Processes)` 
 4| join process_guid [
 5| tstats `security_content_summariesonly` count min(_time) as firstTime max(_time) as lastTime FROM datamodel=Endpoint.Filesystem where Filesystem.file_path IN ("*\\system32\\*", "*\\syswow64\\*") Filesystem.file_name="*.bat" by _time span=1h Filesystem.dest Filesystem.file_create_time Filesystem.file_name Filesystem.file_path Filesystem.process_guid 
 6| `drop_dm_object_name(Filesystem)`] 
 7| table dest user file_create_time, file_name, file_path, process_name, firstTime, lastTime 
 8| dedup file_create_time 
 9| `security_content_ctime(firstTime)` 
10| `security_content_ctime(lastTime)` 
11| `batch_file_write_to_system32_filter`

Data Source

Name	Platform	Sourcetype	Source	Supported App
Sysmon EventID 1	Windows	'xmlwineventlog'	'XmlWinEventLog:Microsoft-Windows-Sysmon/Operational'	N/A

Macros Used

Annotations

Default Configuration

This detection is configured by default in Splunk Enterprise Security to run with the following settings:

Implementation

To successfully implement this search you need to be ingesting information on process that include the name of the process responsible for the changes from your endpoints into the Endpoint datamodel in the Processes node. In addition, confirm the latest CIM App 4.20 or higher is installed and the latest TA for the endpoint product.

Known False Positives

It is possible for this search to generate a notable event for a batch file write to a path that includes the string "system32", but is not the actual Windows system directory. As such, you should confirm the path of the batch file identified by the search. In addition, a false positive may be generated by an administrator copying a legitimate batch file in this directory tree. You should confirm that the activity is legitimate and modify the search to add exclusions, as necessary.

Associated Analytic Story

• SamSam Ransomware

Risk Based Analytics (RBA)

Detection Testing

Replay any dataset to Splunk Enterprise by using our replay.py tool or the UI. Alternatively you can replay a dataset into a Splunk Attack Range

Source: GitHub | Version: 5