Batch File Write to System32

SPLUNK detection rule by Steven Dick, Michael Haag, Rico Valdez, Splunk · Apache-2.0

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.

name: Batch File Write to System32
id: 503d17cb-9eab-4cf8-a20e-01d5c6987ae3
version: 15
creation_date: '2020-04-29'
modification_date: '2026-07-02'
author: Steven Dick, Michael Haag, Rico Valdez, Splunk
status: production
type: Anomaly
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.
data_source:
    - Sysmon EventID 11
search: |-
    | tstats `security_content_summariesonly`
      count min(_time) as firstTime
            max(_time) as lastTime

    FROM datamodel=Endpoint.Filesystem where

    Filesystem.action IN (
        "created",
        "modified"
    )
    Filesystem.file_path IN (
        "*:\\Windows\\System32\\*",
        "*:\\Windows\\SysWOW64\\*"
    )
    Filesystem.file_name IN (
        "*.bat",
        "*.cmd"
    )

    by Filesystem.action Filesystem.dest Filesystem.file_access_time
       Filesystem.file_create_time Filesystem.file_hash
       Filesystem.file_modify_time Filesystem.file_name
       Filesystem.file_path Filesystem.file_acl
       Filesystem.file_size Filesystem.process_guid
       Filesystem.process_id Filesystem.user Filesystem.vendor_product

    | `drop_dm_object_name(Filesystem)`
    | `security_content_ctime(firstTime)`
    | `security_content_ctime(lastTime)`
    | `batch_file_write_to_system32_filter`
how_to_implement: |-
    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.
    You must also be ingesting the Endpoint.Filesystem data source.
known_false_positives: |-
    Some batch files are written to the system32 directory tree for legitimate purposes, such as system maintenance or configuration. Investigate the batch file to determine if it is legitimate and modify the search to add exclusions, as necessary.
references: []
drilldown_searches:
    - name: View the detection results for - "$user$" and "$dest$"
      search: '%original_detection_search% | search  user = "$user$" dest = "$dest$"'
      earliest_offset: $info_min_time$
      latest_offset: $info_max_time$
    - name: View risk events for the last 7 days for - "$user$" and "$dest$"
      search: '| from datamodel Risk.All_Risk | search normalized_risk_object IN ("$user$", "$dest$") | stats count min(_time) as firstTime max(_time) as lastTime values(search_name) as "Search Name" values(risk_message) as "Risk Message" values(analyticstories) as "Analytic Stories" values(annotations._all) as "Annotations" values(annotations.mitre_attack.mitre_tactic) as "ATT&CK Tactics" by normalized_risk_object | `security_content_ctime(firstTime)` | `security_content_ctime(lastTime)`'
      earliest_offset: 7d
      latest_offset: "0"
intermediate_findings:
    entities:
        - field: dest
          type: system
          score: 20
          message: A new batch file [$file_name$] was written to [$file_path$] on endpoint $dest$ by user $user$.
threat_objects:
    - field: file_path
      type: file_path
analytic_story:
    - SamSam Ransomware
    - Compromised Windows Host
asset_type: Endpoint
mitre_attack_id:
    - T1204.002
product:
    - Splunk Enterprise
    - Splunk Enterprise Security
    - Splunk Cloud
category: endpoint
security_domain: endpoint
tests:
    - name: True Positive Test
      attack_data:
        - data: https://media.githubusercontent.com/media/splunk/attack_data/master/datasets/attack_techniques/T1204.002/batch_file_in_system32/windows-sysmon.log
          source: XmlWinEventLog:Microsoft-Windows-Sysmon/Operational
          sourcetype: XmlWinEventLog
      test_type: unit

[[ currentRule.title && currentRule.title.length > 60 ? currentRule.title.slice(0, 60) + '…' : currentRule.title ]]

ec7c1b43-f6f1-46a8-8c40-5a5276af4b57

Propose edits, view related rules, and engage with the community through comments.

Executable code, not a declarative rule

This submission is arbitrary [[ currentRule.format ? currentRule.format.toUpperCase() : '' ]] code, not a declarative detection rule — review it as you would any script before running it, and note that it cannot be safely aggregated or auto-executed alongside YARA/Sigma/Suricata/CRS rules.

Rejected pattern present

[[ reason ]]

What does this mean?

Format & documentation suggestions

Not a security issue — this rule is valid and was accepted as-is. These are optional fields/conventions its own format recommends, mainly affecting its quality score and how well it documents itself for other reviewers.

[[ reason ]]

What do these messages mean?

[[ currentRule.title && currentRule.title.length > 60 ? currentRule.title.slice(0, 60) + '…' : currentRule.title ]]

[[ currentRule.title ]]

Community Discussion