Allow Inbound Traffic In Firewall Rule

name: Allow Inbound Traffic In Firewall Rule
id: a5d85486-b89c-11eb-8267-acde48001122
version: 11
date: '2026-03-10'
author: Teoderick Contreras, Splunk
status: production
type: TTP
description: The following analytic detects a suspicious PowerShell command that allows inbound traffic to a specific local port within the public profile. It leverages PowerShell script block logging (EventCode 4104) to identify commands containing keywords like "firewall," "Inbound," "Allow," and "-LocalPort." This activity is significant because it may indicate an attacker attempting to establish remote access by modifying firewall rules. If confirmed malicious, this could allow unauthorized access to the machine, potentially leading to further exploitation and data exfiltration.
data_source:
    - Powershell Script Block Logging 4104
search: |-
    `powershell` EventCode=4104 ScriptBlockText = "*firewall*" ScriptBlockText = "*Inbound*" ScriptBlockText = "*Allow*"  ScriptBlockText = "*-LocalPort*"
      | fillnull
      | stats count min(_time) as firstTime max(_time) as lastTime
        BY dest signature signature_id
           user_id vendor_product EventID
           Guid Opcode Name
           Path ProcessID ScriptBlockId
           ScriptBlockText
      | `security_content_ctime(firstTime)`
      | `security_content_ctime(lastTime)`
      | `allow_inbound_traffic_in_firewall_rule_filter`
how_to_implement: To successfully implement this search, you need to be ingesting logs with the powershell logs  from your endpoints. make sure you enable needed registry to monitor this event.
known_false_positives: administrator may allow inbound traffic in certain network or machine.
references:
    - https://docs.microsoft.com/en-us/powershell/module/netsecurity/new-netfirewallrule?view=windowsserver2019-ps
drilldown_searches:
    - name: View the detection results for - "$user_id$" and "$dest$"
      search: '%original_detection_search% | search  user_id = "$user_id$" dest = "$dest$"'
      earliest_offset: $info_min_time$
      latest_offset: $info_max_time$
    - name: View risk events for the last 7 days for - "$user_id$" and "$dest$"
      search: '| from datamodel Risk.All_Risk | search normalized_risk_object IN ("$user_id$", "$dest$") 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: Suspicious firewall modification detected on endpoint $dest$ by user $user_id$.
    risk_objects:
        - field: user_id
          type: user
          score: 50
        - field: dest
          type: system
          score: 50
    threat_objects: []
tags:
    analytic_story:
        - Prohibited Traffic Allowed or Protocol Mismatch
        - NetSupport RMM Tool Abuse
    asset_type: Endpoint
    mitre_attack_id:
        - T1021.001
    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/T1021/allow_inbound_traffic_in_firewall_rule/windows-xml.log
          source: XmlWinEventLog:Microsoft-Windows-PowerShell/Operational
          sourcetype: XmlWinEventLog