Detection rules › Splunk
ESXi SSH Brute Force
This detection identifies signs of SSH brute-force attacks by monitoring for a high number of failed login attempts within a short time frame. Such activity may indicate an attacker attempting to gain unauthorized access through password guessing.
MITRE ATT&CK coverage
| Tactic | Techniques |
|---|---|
| Credential Access | T1110 Brute Force |
Rule body splunk
name: ESXi SSH Brute Force
id: 68fe4efa-bbbb-44ee-9f09-d07d2f0f346b
version: 5
creation_date: '2025-07-11'
modification_date: '2026-05-13'
author: Raven Tait, Splunk
status: production
type: Anomaly
description: This detection identifies signs of SSH brute-force attacks by monitoring for a high number of failed login attempts within a short time frame. Such activity may indicate an attacker attempting to gain unauthorized access through password guessing.
data_source:
- VMWare ESXi Syslog
search: '`esxi_syslog` Message="*Authentication failure for*" | rex "for (?<user>[\w]+) from (?<src_ip>\d{1,3}\.\d{1,3}\.\d{1,3}\.\d{1,3})" | rex field=_raw "Z (?<dest>[\w\.]+)\s" | bin _time span=5m | stats min(_time) as firstTime max(_time) as lastTime count by user, src_ip, dest | where count > 10 | `security_content_ctime(firstTime)` | `security_content_ctime(lastTime)` | `esxi_ssh_brute_force_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: Attempted SSH brute force on ESXi host $dest$.
analytic_story:
- Hellcat Ransomware
- ESXi Post Compromise
- Black Basta Ransomware
asset_type: Infrastructure
mitre_attack_id:
- T1110
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/T1110/esxi_ssh_brute_force/esxi_ssh_brute_force.log
source: vmware:esxlog
sourcetype: vmw-syslog
test_type: unit
Stages and Predicates
Stage 1: search
`esxi_syslog` Message="*Authentication failure for*"
Stage 2: rex
| rex "for (?<user>[\w]+) from (?<src_ip>\d{1,3}\.\d{1,3}\.\d{1,3}\.\d{1,3})"
Stage 3: rex
| rex field=_raw "Z (?<dest>[\w\.]+)\s"
Stage 4: bucket
| bin _time span=5m
Stage 5: stats
| stats min(_time) as firstTime max(_time) as lastTime count by user, src_ip, dest
Stage 6: where
| where count > 10
Stage 7: search
| `security_content_ctime(firstTime)`
Stage 8: search
| `security_content_ctime(lastTime)`
Stage 9: search
| `esxi_ssh_brute_force_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 | eq |
|
count | gt |
|
sourcetype | in |
|