ESXi Firewall Disabled

name: ESXi Firewall Disabled
id: e321804c-8eb5-42f2-a843-36b289a6c6b2
version: 6
creation_date: '2025-07-11'
modification_date: '2026-05-13'
author: Raven Tait, Splunk
status: production
type: TTP
description: This detection identifies when the ESXi firewall is disabled or set to permissive mode, which can expose the host to unauthorized access and network-based attacks. Such changes are often a precursor to lateral movement, data exfiltration, or the installation of malicious software by a threat actor.
data_source:
    - VMWare ESXi Syslog
search: '`esxi_syslog` Message="*network firewall set*" AND Message="*enabled f*" | 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_firewall_disabled_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.
finding:
    title: Firewall disabled on ESXi host $dest$.
    entity:
        field: dest
        type: system
        score: 50
analytic_story:
    - ESXi Post Compromise
    - Black Basta Ransomware
    - China-Nexus Threat Activity
asset_type: Infrastructure
mitre_attack_id:
    - T1686
product:
    - Splunk Enterprise
    - Splunk Enterprise Security
    - Splunk Cloud
category: application
security_domain: endpoint