Cisco Secure Firewall - Repeated Malware Downloads

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

The following analytic detects repeated malware file downloads initiated by the same internal host (src) within a short time window. It leverages Cisco Secure Firewall Threat Defense logs and identifies `FileEvent` events with a `SHA_Disposition` of "Malware" and `FileDirection` set to "Download". If ten or more such events occur from the same host within five minutes, this analytic will trigger. This activity may indicate the host is compromised and repeatedly retrieving malicious content either due to command-and-control, malware staging, or automation. If confirmed malicious, this behavior may represent an infection in progress, persistence mechanism, or a malicious downloader.

name: Cisco Secure Firewall - Repeated Malware Downloads
id: aeff2bb5-3483-48d4-9be8-c8976194be1e
version: 10
creation_date: '2025-04-09'
modification_date: '2026-05-13'
author: Nasreddine Bencherchali, Splunk
status: production
type: Anomaly
description: |
    The following analytic detects repeated malware file downloads initiated by the same internal host (src) within a short time window. It leverages Cisco Secure Firewall Threat Defense logs and identifies `FileEvent` events with a `SHA_Disposition` of "Malware" and `FileDirection` set to "Download". If ten or more such events occur from the same host within five minutes, this analytic will trigger. This activity may indicate the host is compromised and repeatedly retrieving malicious content either due to command-and-control, malware staging, or automation. If confirmed malicious, this behavior may represent an infection in progress, persistence mechanism, or a malicious downloader.
data_source:
    - Cisco Secure Firewall Threat Defense File Event
search: |
    `cisco_secure_firewall` EventType=FileEvent SHA_Disposition="Malware" FileDirection="Download"
    | lookup cisco_secure_firewall_filetype_lookup Name as FileType OUTPUT Description
    | bin _time span=5m
    | stats count min(_time) as firstTime max(_time) as lastTime
            values(uri) as uri
            values(ClientApplication) as ClientApplication
            values(app) as app
            values(file_hash) as file_hash
            values(SHA_Disposition) as SHA_Disposition
            values(file_name) as file_name
            values(ThreatName) as ThreatName
            values(dest) as dest
            values(dest_port) as dest_port
            by src FileDirection FileType Description
    | where count >= 10
    | `security_content_ctime(firstTime)`
    | `security_content_ctime(lastTime)`
    | table firstTime lastTime src dest dest_port FileDirection FileType Description uri file_name file_hash app ClientApplication ThreatName SHA_Disposition
    | `cisco_secure_firewall___repeated_malware_downloads_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: False positives should be minimal here, tuning may be required to exclude known test machines or development hosts.
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: Repeated malware file downloads detected from $src$ involving $ThreatName$.
threat_objects:
    - field: file_hash
      type: file_hash
    - field: file_name
      type: file_name
analytic_story:
    - Hellcat Ransomware
    - 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/file_event/file_events.log
          source: not_applicable
          sourcetype: cisco:sfw:estreamer
      test_type: unit

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