Cisco Secure Firewall - Blocked Connection

SPLUNK detection rule by Nasreddine Bencherchali, Splunk · Apache-2.0

The following analytic detects a blocked connection event by identifying a "Block" value in the action field. It leverages logs from Cisco Secure Firewall Threat Defense devices. This activity is significant as it can identify attempts from users or applications initiating network connection to explicitly or implicitly blocked range or zones. If confirmed malicious, attackers could be attempting to perform a forbidden action on the network such as data exfiltration, lateral movement, or network disruption.

name: Cisco Secure Firewall - Blocked Connection
id: 17e9b764-3a2b-4d36-9751-32d13ce4718b
version: 9
creation_date: '2025-04-03'
modification_date: '2026-05-13'
author: Nasreddine Bencherchali, Splunk
status: production
type: Anomaly
description: The following analytic detects a blocked connection event by identifying a "Block" value in the action field. It leverages logs from Cisco Secure Firewall Threat Defense devices. This activity is significant as it can identify attempts from users or applications initiating network connection to explicitly or implicitly blocked range or zones. If confirmed malicious, attackers could be attempting to perform a forbidden action on the network such as data exfiltration, lateral movement, or network disruption.
data_source:
    - Cisco Secure Firewall Threat Defense Connection Event
search: |
    `cisco_secure_firewall` EventType=ConnectionEvent action IN ("Block with reset", "Block", "blocked")
    | stats count min(_time) as firstTime max(_time) as lastTime by src, dest, dest_port, transport, rule, url, EVE_Process, action
    | `security_content_ctime(firstTime)`
    | `security_content_ctime(lastTime)`
    | `cisco_secure_firewall___blocked_connection_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.
known_false_positives: Blocked connection events are generated via an Access Control policy on the Firewall management console. Hence no false positives should be present.
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 ("$src$") | 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: A connection request from $src$ to $dest$ has been blocked according to the configured firewall rule $rule$
threat_objects:
    - field: EVE_Process
      type: process_name
    - field: url
      type: url
analytic_story:
    - Cisco Secure Firewall Threat Defense Analytics
asset_type: Network
mitre_attack_id:
    - T1018
    - T1046
    - T1110
    - T1203
    - T1595.002
product:
    - Splunk Enterprise
    - Splunk Enterprise Security
    - Splunk Cloud
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/connection_event/connection_events.log
          source: not_applicable
          sourcetype: cisco:sfw:estreamer
      test_type: unit

[[ currentRule.title && currentRule.title.length > 60 ? currentRule.title.slice(0, 60) + '…' : currentRule.title ]]

0c7e6dbb-1ff6-435e-b0d3-695ae10c3116

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Executable code, not a declarative rule

This submission is arbitrary [[ currentRule.format ? currentRule.format.toUpperCase() : '' ]] code, not a declarative detection rule — review it as you would any script before running it, and note that it cannot be safely aggregated or auto-executed alongside YARA/Sigma/Suricata/CRS rules.

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Format & documentation suggestions

Not a security issue — this rule is valid and was accepted as-is. These are optional fields/conventions its own format recommends, mainly affecting its quality score and how well it documents itself for other reviewers.

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