Windows WSUS Spawning Shell

name: Windows WSUS Spawning Shell
id: 76ea28ac-6f10-43fd-b5fe-340022ad0fd3
version: 3
date: '2026-03-10'
author: Michael Haag, Splunk
status: production
type: TTP
description: The following analytic identifies instances where a shell (PowerShell.exe or Cmd.exe) is spawned from wsusservice.exe, the Windows Server Update Services process. This detection leverages data from Endpoint Detection and Response (EDR) agents, focusing on process creation events where the parent process is wsusservice.exe. This activity is significant as it may indicate exploitation of CVE-2025-59287, a critical deserialization vulnerability in WSUS that allows unauthenticated remote code execution. If confirmed malicious, this behavior could allow attackers to execute arbitrary commands on WSUS servers, potentially leading to system compromise, data exfiltration, domain enumeration, or further lateral movement within the network.
data_source:
    - Sysmon EventID 1
    - Windows Event Log Security 4688
    - CrowdStrike ProcessRollup2
search: |-
    | tstats `security_content_summariesonly` count values(Processes.process_name) as process_name values(Processes.process) as process min(_time) as firstTime max(_time) as lastTime FROM datamodel=Endpoint.Processes
      WHERE Processes.parent_process_name=wsusservice.exe
        AND
        `process_cmd`
        OR
        `process_powershell`
      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_wsus_spawning_shell_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: Legitimate WSUS maintenance scripts or administrative tools may spawn shells in rare cases. However, wsusservice.exe spawning interactive shells is highly abnormal behavior. Review the command line arguments and user context to determine legitimacy. Filter known administrative scripts if needed.
references:
    - https://www.huntress.com/blog/exploitation-of-windows-server-update-services-remote-code-execution-vulnerability
    - https://msrc.microsoft.com/update-guide/vulnerability/CVE-2025-59287
    - https://hawktrace.com/blog/CVE-2025-59287-UNAUTH
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 ("$dest$") starthoursago=168  | 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: $info_min_time$
      latest_offset: $info_max_time$
rba:
    message: WSUS service process wsusservice.exe spawned shell process $process_name$ on $dest$ by $user$, indicating possible CVE-2025-59287 exploitation
    risk_objects:
        - field: dest
          type: system
          score: 50
        - field: user
          type: user
          score: 50
    threat_objects:
        - field: process_name
          type: process_name
tags:
    analytic_story:
        - Microsoft WSUS CVE-2025-59287
    asset_type: Endpoint
    cve:
        - CVE-2025-59287
    mitre_attack_id:
        - T1190
        - T1505.003
    product:
        - Splunk Enterprise
        - Splunk Enterprise Security
        - Splunk Cloud
    security_domain: endpoint
tests:
    - name: True Positive Test
      attack_data:
        - data: https://media.githubusercontent.com/media/splunk/attack_data/master/datasets/attack_techniques/T1505.003/wsus-windows-sysmon.log
          sourcetype: XmlWinEventLog
          source: XmlWinEventLog:Microsoft-Windows-Sysmon/Operational