splunk-security_content/detections/endpoint/linux_iptables_firewall_modification.yml

name: Linux Iptables Firewall Modification
id: 309d59dc-1e1b-49b2-9800-7cf18d12f7b7
version: 11
date: '2025-05-02'
author: Teoderick Contreras, Splunk
status: production
type: Anomaly
description: The following analytic detects suspicious command-line activity that
  modifies the iptables firewall settings on a Linux machine. It leverages data from
  Endpoint Detection and Response (EDR) agents, focusing on specific command patterns
  that alter firewall rules to accept traffic on certain TCP ports. This activity
  is significant as it can indicate malware, such as CyclopsBlink, modifying firewall
  settings to allow communication with a Command and Control (C2) server. If confirmed
  malicious, this could enable attackers to maintain persistent access and exfiltrate
  data, posing a severe security risk.
data_source:
- Sysmon for Linux EventID 1
search: '| tstats `security_content_summariesonly` count min(_time) as firstTime max(_time)
  as lastTime from datamodel=Endpoint.Processes where Processes.process = "*iptables
  *" AND Processes.process = "* --dport *" AND Processes.process = "* ACCEPT*" AND
  Processes.process = "*&>/dev/null*" AND Processes.process = "* tcp *" AND
  NOT(Processes.parent_process_path IN("/bin/*", "/lib/*", "/usr/bin/*", "/sbin/*"))
  by Processes.action Processes.dest Processes.original_file_name Processes.parent_process
  Processes.parent_process_exec Processes.parent_process_guid Processes.parent_process_id
  Processes.parent_process_name Processes.parent_process_path Processes.process Processes.process_exec
  Processes.process_guid Processes.process_hash Processes.process_id Processes.process_integrity_level
  Processes.process_name Processes.process_path Processes.user Processes.user_id Processes.vendor_product
  | rex field=Processes.process "--dport (?<port>3269|636|989|994|995|8443)" | stats
  values(Processes.process) as processes_exec values(port) as ports values(Processes.process_guid)
  as guids values(Processes.process_id) as pids dc(port) as port_count count by Processes.process_name
  Processes.parent_process_name Processes.parent_process_id Processes.dest Processes.user
  Processes.parent_process_path Processes.process_path | where port_count >=3 | `drop_dm_object_name(Processes)`
  | `security_content_ctime(firstTime)` | `security_content_ctime(lastTime)` | `linux_iptables_firewall_modification_filter`'
how_to_implement: The detection is based on data that originates from Endpoint Detection
  and Response (EDR) agents. These agents are designed to provide security-related
  telemetry from the endpoints where the agent is installed. To implement this search,
  you must ingest logs that contain the process GUID, process name, and parent process.
  Additionally, you must ingest complete command-line executions. These logs must
  be processed using the appropriate Splunk Technology Add-ons that are specific to
  the EDR product. The logs must also be mapped to the `Processes` node of the `Endpoint`
  data model. Use the Splunk Common Information Model (CIM) to normalize the field
  names and speed up the data modeling process.
known_false_positives: administrator may do this commandline for auditing and testing
  purposes. In this scenario filter is needed.
references:
- https://www.ncsc.gov.uk/files/Cyclops-Blink-Malware-Analysis-Report.pdf
- https://www.trendmicro.com/en_us/research/22/c/cyclops-blink-sets-sights-on-asus-routers--.html
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: A process name - $process_name$ that may modify iptables firewall on $dest$
  risk_objects:
  - field: dest
    type: system
    score: 25
  threat_objects: []
tags:
  analytic_story:
  - China-Nexus Threat Activity
  - Backdoor Pingpong
  - Cyclops Blink
  - Sandworm Tools
  asset_type: Endpoint
  mitre_attack_id:
  - T1562.004
  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/malware/cyclopsblink/sysmon_linux.log
    source: Syslog:Linux-Sysmon/Operational
    sourcetype: sysmon:linux