Detection: Batch File Write to System32

Updated Date: 2024-12-10 ID: 503d17cb-9eab-4cf8-a20e-01d5c6987ae3 Author: Steven Dick, Michael Haag, Rico Valdez, Splunk Type: TTP Product: Splunk Enterprise Security

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
Sysmon EventID 1	Windows	`'xmlwineventlog'`	`'XmlWinEventLog:Microsoft-Windows-Sysmon/Operational'`
Sysmon EventID 11	Windows	`'xmlwineventlog'`	`'XmlWinEventLog:Microsoft-Windows-Sysmon/Operational'`

Macros Used

Name	Value
security_content_ctime	`convert timeformat="%Y-%m-%dT%H:%M:%S" ctime($field$)`
batch_file_write_to_system32_filter	`search *`

batch_file_write_to_system32_filter is an empty macro by default. It allows the user to filter out any results (false positives) without editing the SPL.

Annotations

- MITRE ATT&CK

+ Kill Chain Phases

+ NIST

+ CIS

- Threat Actors

ID	Technique	Tactic
T1204	User Execution	Execution
T1204.002	Malicious File	Execution

Installation

DE.CM

CIS 10

Default Configuration

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

Setting	Value
Disabled	true
Cron Schedule	`0 * * * *`
Earliest Time	`-70m@m`
Latest Time	`-10m@m`
Schedule Window	`auto`
Creates Notable	Yes
Rule Title	`%name%`
Rule Description	`%description%`
Notable Event Fields	user, dest
Creates Risk Event	True

This configuration file applies to all detections of type TTP. These detections will use Risk Based Alerting and generate Notable Events.

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 finding 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

Risk Based Analytics (RBA)

Risk Message:

A file - $file_name$ was written to system32 has occurred on endpoint $dest$ by user $user$.

Risk Object	Risk Object Type	Risk Score	Threat Objects
user	user	63	file_name
dest	system	63	file_name

Detection Testing

Test Type	Status	Dataset	Source	Sourcetype
Validation	✅ Passing	N/A	N/A	N/A
Unit	✅ Passing	Dataset	`XmlWinEventLog:Microsoft-Windows-Sysmon/Operational`	`XmlWinEventLog`
Integration	✅ Passing	Dataset	`XmlWinEventLog:Microsoft-Windows-Sysmon/Operational`	`XmlWinEventLog`

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: 8