Cisco Secure Firewall - Snort Rule Triggered Across Multiple Hosts

name: Cisco Secure Firewall - Snort Rule Triggered Across Multiple Hosts
id: a4c76d0a-56b6-44be-814b-939746c4d406
version: 8
creation_date: '2025-04-16'
modification_date: '2026-05-13'
author: Nasreddine Bencherchali, Splunk
status: production
type: Anomaly
description: |
    This analytic identifies Snort intrusion signatures that have been triggered by ten or more distinct internal IP addresses within a one-hour window. It leverages Cisco Secure Firewall Threat Defense logs and focuses on the IntrusionEvent event type to detect activity that may indicate broad targeting or mass exploitation attempts. This behavior is often associated with opportunistic scanning, worm propagation, or automated exploitation of known vulnerabilities across multiple systems. If confirmed malicious, this could represent the early phase of a coordinated attack aiming to gain a foothold on several hosts or move laterally across the environment.
data_source:
    - Cisco Secure Firewall Threat Defense Intrusion Event
search: |
    `cisco_secure_firewall` EventType=IntrusionEvent
    | bin _time span=1h
    | stats dc(src) as unique_src_ips, values(src) as src
            min(_time) as firstTime max(_time) as lastTime
            Values(dest) as dest
            Values(dest_port) as dest_port
            Values(rule) as rule
            Values(transport) as transport
            Values(app) as app
            by signature_id, signature class_desc MitreAttackGroups InlineResult InlineResultReason
    | where unique_src_ips >= 10
    | `security_content_ctime(firstTime)`
    | `security_content_ctime(lastTime)`
    | `cisco_secure_firewall___snort_rule_triggered_across_multiple_hosts_filter`
how_to_implement: |
    This search requires Cisco Secure Firewall Threat Defense Logs, which
    includes the IntrusionEvent 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 intrusion access policy must also be configured.
known_false_positives: False positives should be minimal. Simultaneous vulnerability scanning across multiple internal hosts might trigger this, as well as some snort rules that are noisy. Disable those if necessary or increase the threshold.
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 - "$src$" and "$signature_id$"
      search: '%original_detection_search% | search  src = "$src$" and signature_id = "$signature_id$"'
      earliest_offset: $info_min_time$
      latest_offset: $info_max_time$
    - name: View risk events for the last 7 days for - "$src$" and "$signature_id$"
      search: '| from datamodel Risk.All_Risk | search normalized_risk_object IN ("$src$", "$signature_id$") | 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"
intermediate_findings:
    entities:
        - field: src
          type: system
          score: 20
          message: The Snort rule $signature$ was triggered by $unique_src_ips$ unique internal hosts within a one-hour window, indicating potential widespread exploitation or coordinated targeting activity.
threat_objects:
    - field: signature
      type: signature
analytic_story:
    - Cisco Secure Firewall Threat Defense Analytics
asset_type: Network
mitre_attack_id:
    - T1105
    - T1027
product:
    - Splunk Enterprise
    - Splunk Cloud
    - Splunk Enterprise Security
category: network
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
      test_type: unit