Cisco Secure Firewall - Communication Over Suspicious Ports

name: Cisco Secure Firewall - Communication Over Suspicious Ports
id: d85c05c8-42c0-4e4a-87e7-4e1bb3e844e3
version: 6
date: '2026-03-10'
author: Nasreddine Bencherchali, Splunk
status: production
type: Anomaly
description: |
    The following analytic detects potential reverse shell activity by identifying connections involving ports commonly associated with remote access tools, shell listeners, or tunneling utilities. It leverages Cisco Secure Firewall Threat Defense logs and monitors destination ports against a list of non-standard, high-risk port values often used in post-exploitation scenarios. Adversaries frequently configure tools like netcat, Meterpreter, or other backdoors to listen or connect over uncommon ports such as 4444, 2222, or 51820 to bypass standard monitoring and firewall rules. If confirmed malicious, this activity may represent command and control (C2) tunneling, lateral movement, or unauthorized remote access.
data_source:
    - Cisco Secure Firewall Threat Defense Connection Event
search: |
    `cisco_secure_firewall` EventType=ConnectionEvent dest_port IN ("888", "999", "2200", "2222", "4000", "4444", "6789", "8531", "50501", "51820") | fillnull value="unknown" url
    | stats min(_time) as firstTime max(_time) as lastTime
          values(src_port) as src_port
          values(url) as url
          values(rule) as rule
          count by src, dest, dest_port, transport, action
    | `security_content_ctime(firstTime)`
    | `security_content_ctime(lastTime)`
    | `cisco_secure_firewall___communication_over_suspicious_ports_filter`
how_to_implement: |
    This search requires Cisco Secure Firewall Threat Defense Logs, which
    includes the ConnectionEvent EventType. This search uses an input macro named `cisco_secure_firewall`.
    We strongly recommend that you specify your environment-specific configurations
    (index, source, sourcetype, etc.) for Cisco Secure Firewall Threat Defense logs. Replace the macro definition
    with configurations for your Splunk environment. The search also uses a post-filter
    macro designed to filter out known false positives.
    The logs are to be ingested using the Splunk Add-on for Cisco Security Cloud (https://splunkbase.splunk.com/app/7404).
    The access policy must also enable logging.
    The search uses a hardcoded list of suspicious ports, you might want to tune those according to your environment
known_false_positives: |
    Some legitimate services or custom applications may use non-standard ports for development, remote management, or internal communication.
    Ephemeral ports in test environments may occasionally overlap with ports used in this detection.
    Additional context such as process name, user behavior, or endpoint telemetry should be used to validate suspicious sessions before escalation.
references:
    - https://www.cisco.com/c/en/us/td/docs/security/firepower/741/api/FQE/secure_firewall_estreamer_fqe_guide_740.pdf
drilldown_searches:
    - name: View the detection results for - "$src$"
      search: '%original_detection_search% | search  src = "$src$"'
      earliest_offset: $info_min_time$
      latest_offset: $info_max_time$
    - name: View risk events for the last 7 days for - "$src$"
      search: '| from datamodel Risk.All_Risk | search normalized_risk_object IN ("$src$") 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 communication detected from $src$ to $dest$ over port $dest_port$.
    risk_objects:
        - field: src
          type: system
          score: 20
    threat_objects:
        - field: url
          type: url
tags:
    analytic_story:
        - Cisco Secure Firewall Threat Defense Analytics
    asset_type: Network
    security_domain: network
    mitre_attack_id:
        - T1021
        - T1055
        - T1059.001
        - T1105
        - T1219
        - T1571
    product:
        - Splunk Enterprise
        - Splunk Cloud
        - Splunk Enterprise Security
tests:
    - name: True Positive Test
      attack_data:
        - data: https://media.githubusercontent.com/media/splunk/attack_data/master/datasets/cisco_secure_firewall_threat_defense/connection_event/connection_events.log
          source: not_applicable
          sourcetype: cisco:sfw:estreamer