splunk_escuAnomaly

ESXi Download Errors

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

MITRE ATT&CK

T1601.001 T1562.001

Detection Query

`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`

Author

Raven Tait, Splunk

Created

2026-03-10

Data Sources

VMWare ESXi Syslog

Tags

ESXi Post CompromiseBlack Basta Ransomware

Raw Content

name: ESXi Download Errors
id: 515cccd0-c4d8-4427-92d9-8a8f8b5a71dc
version: 2
date: '2026-03-10'
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.
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: Download Errors on ESXi host $dest$.
    risk_objects:
        - field: dest
          type: system
          score: 20
    threat_objects: []
tags:
    analytic_story:
        - ESXi Post Compromise
        - Black Basta Ransomware
    asset_type: Infrastructure
    mitre_attack_id:
        - T1601.001
        - T1562.001
    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/T1601.001/esxi_download_errors/esxi_download_errors.log
          source: vmware:esxlog
          sourcetype: vmw-syslog