ESXi Download Errors

Name:ESXi Download Errors
id:515cccd0-c4d8-4427-92d9-8a8f8b5a71dc
version:1
date:2025-05-12
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.
References:
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:'$info_max_time$'
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
manual_test:None