Detection rules › Splunk
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 coverage
| Tactic | Techniques |
|---|---|
| Defense Impairment | T1601.001 Modify System Image: Patch System Image, T1685 Disable or Modify Tools |
Rule body splunk
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.
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: 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
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
test_type: unit
Stages and Predicates
Stage 1: search
`esxi_syslog` Message IN ("*Download failed*", "*Failed to download file*", "*File download error*", "*Could not download*")
Stage 2: rex
| rex field=_raw "Z (?<dest>[\w\.]*)\s"
Stage 3: stats
| stats min(_time) as firstTime max(_time) as lastTime count by dest Message
Stage 4: search
| `security_content_ctime(firstTime)`
Stage 5: search
| `security_content_ctime(lastTime)`
Stage 6: search
| `esxi_download_errors_filter`
Indicators
Each row is a field, operator, and value that the rule matches. The corpus column counts how many other rules in the catalog look for the same combination: high numbers point to widely-used, community-vetted indicators. Blank or 1 shows that the indicator is specific to this rule.
| Field | Kind | Values |
|---|---|---|
Message | in |
|
sourcetype | in |
|