ESXi Download Errors

name: ESXi Download Errors
id: 515cccd0-c4d8-4427-92d9-8a8f8b5a71dc
version: 5
creation_date: '2025-07-11'
modification_date: '2026-05-13'
author: Raven Tait, Splunk
status: production
type: Anomaly
description: This detection identifies failed file download attempts on ESXi hosts by looking for specific error messages in the system logs. These failures may indicate unauthorized or malicious attempts to install or update components—such as VIBs or scripts
data_source:
    - VMWare ESXi Syslog
search: '`esxi_syslog` Message IN ("*Download failed*", "*Failed to download file*", "*File download error*", "*Could not download*") | rex field=_raw "Z (?<dest>[\w\.]*)\s" | stats min(_time) as firstTime max(_time) as lastTime count by dest Message | `security_content_ctime(firstTime)` | `security_content_ctime(lastTime)` | `esxi_download_errors_filter` '
how_to_implement: This is based on syslog data generated by VMware ESXi hosts. To implement this search, you must configure your ESXi systems to forward syslog output to your Splunk deployment. These logs must be ingested with the appropriate Splunk Technology Add-on for VMware ESXi Logs, which provides field extractions and CIM compatibility.
known_false_positives: Limited false positives in most environments, however tune as needed.
intermediate_findings:
    entities:
        - field: dest
          type: system
          score: 20
          message: Download Errors on ESXi host $dest$.
analytic_story:
    - ESXi Post Compromise
    - Black Basta Ransomware
asset_type: Infrastructure
mitre_attack_id:
    - T1601.001
    - T1685
product:
    - Splunk Enterprise
    - Splunk Enterprise Security
    - Splunk Cloud
category: application
security_domain: endpoint