splunk_escuAnomaly

Cisco Secure Firewall - SSH Connection to Non-Standard Port

This analytic detects inbound SSH connections to non-standard ports on network devices using Cisco Secure Firewall Intrusion Events. APT actors have been observed enabling SSH servers on high, non-default TCP ports to maintain encrypted remote access to compromised network infrastructure. This detection leverages Snort signature 65369 to identify SSH protocol traffic on unusual ports, which may indicate persistence mechanisms or backdoor access established by threat actors.

MITRE ATT&CK

T1021.004

lateral-movement

Detection Query

`cisco_secure_firewall`
EventType=IntrusionEvent
signature_id=65369
| fillnull
| stats dc(signature_id) as unique_signature_count
        values(signature_id) as signature_id
        values(signature) as signature
        values(class_desc) as class_desc
        values(MitreAttackGroups) as MitreAttackGroups
        values(InlineResult) as InlineResult
        values(InlineResultReason) as InlineResultReason
        values(src) as src
        values(dest_port) as dest_port
        values(rule) as rule
        values(transport) as transport
        values(app) as app
        min(_time) as firstTime
        max(_time) as lastTime
        by dest
| `security_content_ctime(firstTime)`
| `security_content_ctime(lastTime)`
| `cisco_secure_firewall___ssh_connection_to_non_standard_port_filter`

Author

Nasreddine Bencherchali, Michael Haag, Splunk

Created

2026-03-10

Data Sources

Cisco Secure Firewall Threat Defense Intrusion Event

References

https://www.cisa.gov/news-events/cybersecurity-advisories/aa25-239a

Tags

Cisco Secure Firewall Threat Defense AnalyticsSalt Typhoon

Raw Content

name: Cisco Secure Firewall - SSH Connection to Non-Standard Port
id: 9b0c2d3e-4f5a-6b7c-8d9e-0f1a2b3c4d5e
version: 3
date: '2026-03-10'
author: Nasreddine Bencherchali, Michael Haag, Splunk
status: production
type: Anomaly
description: |
    This analytic detects inbound SSH connections to non-standard ports on network devices using Cisco Secure Firewall Intrusion Events. APT actors have been observed enabling SSH servers on high, non-default TCP ports to maintain encrypted remote access to compromised network infrastructure.
    This detection leverages Snort signature 65369 to identify SSH protocol traffic on unusual ports, which may indicate persistence mechanisms or backdoor access established by threat actors.
data_source:
    - Cisco Secure Firewall Threat Defense Intrusion Event
search: |
    `cisco_secure_firewall`
    EventType=IntrusionEvent
    signature_id=65369
    | fillnull
    | stats dc(signature_id) as unique_signature_count
            values(signature_id) as signature_id
            values(signature) as signature
            values(class_desc) as class_desc
            values(MitreAttackGroups) as MitreAttackGroups
            values(InlineResult) as InlineResult
            values(InlineResultReason) as InlineResultReason
            values(src) as src
            values(dest_port) as dest_port
            values(rule) as rule
            values(transport) as transport
            values(app) as app
            min(_time) as firstTime
            max(_time) as lastTime
            by dest
    | `security_content_ctime(firstTime)`
    | `security_content_ctime(lastTime)`
    | `cisco_secure_firewall___ssh_connection_to_non_standard_port_filter`
how_to_implement: |
    This search requires Cisco Secure Firewall Threat Defense Logs, which
    includes the FileEvent 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 malware & file access policy must also enable logging.
known_false_positives: |
    No false positives have been identified yet.
references:
    - https://www.cisa.gov/news-events/cybersecurity-advisories/aa25-239a
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: Inbound SSH connection to non-standard port $dest_port$ detected from $src$ to network device $dest$
    risk_objects:
        - field: dest
          type: system
          score: 20
    threat_objects:
        - field: src
          type: ip_address
tags:
    analytic_story:
        - Cisco Secure Firewall Threat Defense Analytics
        - Salt Typhoon
    asset_type: Network
    mitre_attack_id:
        - T1021.004
    product:
        - Splunk Enterprise
        - Splunk Enterprise Security
        - Splunk Cloud
    security_domain: network
tests:
    - name: True Positive Test
      attack_data:
        - data: https://media.githubusercontent.com/media/splunk/attack_data/master/datasets/cisco_secure_firewall_threat_defense/intrusion_event/intrusion_events.log
          source: not_applicable
          sourcetype: cisco:sfw:estreamer