Windows Symlink Evaluation Change via Fsutil

name: Windows Symlink Evaluation Change via Fsutil
id: 9777e7e3-2499-4a16-a519-ebe33630c1e8
version: 5
creation_date: '2025-10-13'
modification_date: '2026-05-13'
author: Nasreddine Bencherchali, Splunk
status: production
type: Anomaly
description: |
    This analytic detects the execution of the Windows built-in tool Fsutil.exe with
    the "behavior", "set" and "SymlinkEvaluation" parameters.
    Attackers can abuse this to alter symlink evaluation behavior on Windows, potentially enabling remote traversal over SMB shares or evading defenses.
    Such changes should be uncommon or even rare in enterprise environments and should be investigated.
data_source:
    - Sysmon EventID 1
    - Windows Event Log Security 4688
    - CrowdStrike ProcessRollup2
search: |
    | tstats `security_content_summariesonly`
        count min(_time) as firstTime max(_time) as lastTime
      from datamodel=Endpoint.Processes where
    
      (
        Processes.process_name="fsutil.exe"
        OR Processes.original_file_name="fsutil.exe"
      )
    
      Processes.process="*behavior*"
      Processes.process="*set*"
      Processes.process="*SymlinkEvaluation*"
    
      by Processes.action Processes.dest Processes.original_file_name Processes.parent_process
      Processes.parent_process_exec Processes.parent_process_guid Processes.parent_process_id
      Processes.parent_process_name Processes.parent_process_path Processes.process Processes.process_exec
      Processes.process_guid Processes.process_hash Processes.process_id Processes.process_integrity_level
      Processes.process_name Processes.process_path Processes.user Processes.user_id Processes.vendor_product
    
    | `drop_dm_object_name(Processes)`
    | `security_content_ctime(firstTime)`
    | `security_content_ctime(lastTime)`
    | `windows_symlink_evaluation_change_via_fsutil_filter`
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: |
    Edge cases may exist in environments where this command is used for legitimate purposes.
    However, such usage is expected to be uncommon. It is recommended to investigate any occurrences of this command, and apply filters as necessary.
references:
    - https://learn.microsoft.com/windows-server/administration/windows-commands/fsutil-behavior
    - https://www.group-ib.com/blog/blackcat/
    - https://www.intrinsec.com/alphv-ransomware-gang-analysis/
drilldown_searches:
    - name: View the detection results for - "$dest$"
      search: '%original_detection_search% | search  dest = "$dest$"'
      earliest_offset: $info_min_time$
      latest_offset: $info_max_time$
    - name: View risk events for the last 7 days for - "$dest$"
      search: '| from datamodel Risk.All_Risk | search normalized_risk_object IN ("$dest$") | 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: process $process_name$ with command line "$process$" modified SymlinkEvaluation on $dest$
threat_objects:
    - field: parent_process_name
      type: parent_process_name
analytic_story:
    - Windows Post-Exploitation
asset_type: Endpoint
mitre_attack_id:
    - T1222.001
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/T1222.001/fsutil_symlink_eval/fsutil_symlink_eval.log
          source: XmlWinEventLog:Microsoft-Windows-Sysmon/Operational
          sourcetype: XmlWinEventLog
      test_type: unit