splunk_escuAnomaly

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

T1110

Detection Query

`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`

Author

Raven Tait, Splunk

Created

2026-03-10

Data Sources

VMWare ESXi Syslog

Tags

Hellcat RansomwareESXi Post CompromiseBlack Basta Ransomware

Raw Content

name: ESXi SSH Brute Force
id: 68fe4efa-bbbb-44ee-9f09-d07d2f0f346b
version: 3
date: '2026-03-10'
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 ("$dest$") 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: Attempted SSH brute force on ESXi host $dest$.
    risk_objects:
        - field: dest
          type: system
          score: 20
    threat_objects: []
tags:
    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
    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