Allow Inbound Traffic By Firewall Rule Registry

name: Allow Inbound Traffic By Firewall Rule Registry
id: 0a46537c-be02-11eb-92ca-acde48001122
version: 15
creation_date: '2021-05-26'
modification_date: '2026-05-13'
author: Teoderick Contreras, Splunk, Steven Dick
status: production
type: TTP
description: The following analytic detects suspicious modifications to firewall rule registry settings that allow inbound traffic on specific ports with a public profile. It leverages data from the Endpoint.Registry data model, focusing on registry paths and values indicative of such changes. This activity is significant as it may indicate an adversary attempting to grant remote access to a machine by modifying firewall rules. If confirmed malicious, this could enable unauthorized remote access, potentially leading to further exploitation, data exfiltration, or lateral movement within the network.
data_source:
    - Sysmon EventID 13
search: '| tstats `security_content_summariesonly` count min(_time) as firstTime max(_time) as lastTime FROM datamodel=Endpoint.Registry WHERE (Registry.registry_path= "*\\System\\CurrentControlSet\\Services\\SharedAccess\\Parameters\\FirewallPolicy\\FirewallRules\\*" Registry.registry_value_data = "*|Action=Allow|*" Registry.registry_value_data = "*|Dir=In|*"  Registry.registry_value_data = "*|LPort=*") by Registry.action Registry.dest Registry.process_guid Registry.process_id Registry.registry_hive Registry.registry_path Registry.registry_key_name Registry.registry_value_data Registry.registry_value_name Registry.registry_value_type Registry.status Registry.user Registry.vendor_product | `drop_dm_object_name(Registry)` | `security_content_ctime(firstTime)` | `security_content_ctime(lastTime)` | `allow_inbound_traffic_by_firewall_rule_registry_filter`'
how_to_implement: To successfully implement this search, you need to be ingesting logs with the registry value name, registry path, and registry value data from your endpoints. If you are using Sysmon, you must have at least version 2.0 of the official Sysmon TA. https://splunkbase.splunk.com/app/5709
known_false_positives: network admin may add/remove/modify public inbound firewall rule that may cause this rule to be triggered.
references:
    - https://docs.microsoft.com/en-us/powershell/module/netsecurity/new-netfirewallrule?view=windowsserver2019-ps
drilldown_searches:
    - name: View the detection results for - "$user$" and "$dest$"
      search: '%original_detection_search% | search  user = "$user$" dest = "$dest$"'
      earliest_offset: $info_min_time$
      latest_offset: $info_max_time$
    - name: View risk events for the last 7 days for - "$user$" and "$dest$"
      search: '| from datamodel Risk.All_Risk | search normalized_risk_object IN ("$user$", "$dest$") | 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"
finding:
    title: Suspicious firewall allow rule modifications were detected via the registry on endpoint $dest$ by user $user$.
    entity:
        field: user
        type: user
        score: 50
intermediate_findings:
    entities:
        - field: dest
          type: system
          score: 50
          message: Suspicious firewall allow rule modifications were detected via the registry on endpoint $dest$ by user $user$.
analytic_story:
    - Windows Registry Abuse
    - NjRAT
    - PlugX
    - Prohibited Traffic Allowed or Protocol Mismatch
    - Medusa Ransomware
    - Azorult
asset_type: Endpoint
mitre_attack_id:
    - T1021.001
product:
    - Splunk Enterprise
    - Splunk Enterprise Security
    - Splunk Cloud
category: endpoint
security_domain: endpoint
tests:
    - name: True Positive Test
      attack_data:
        - data: https://media.githubusercontent.com/media/splunk/attack_data/master/datasets/honeypots/casper/datasets1/windows-sysmon.log
          source: XmlWinEventLog:Microsoft-Windows-Sysmon/Operational
          sourcetype: XmlWinEventLog
      test_type: unit