Detect Large ICMP Traffic

SPLUNK detection rule by Rico Valdez, Dean Luxton, Bhavin Patel, Splunk · Apache-2.0

The following analytic identifies ICMP traffic to external IP addresses with total bytes (sum of bytes in and bytes out) greater than 1,000 bytes. It leverages the Network_Traffic data model to detect large ICMP packet that aren't blocked and are directed toward external networks. We use All_Traffic.bytes in the detection to capture variations in inbound versus outbound traffic sizes, as significant discrepancies or unusually large ICMP exchanges can indicate information smuggling, covert communication, or command-and-control (C2) activities. If validated as malicious, this could signal ICMP tunneling, unauthorized data transfer, or compromised endpoints requiring immediate investigation.

name: Detect Large ICMP Traffic
id: 9cd6d066-94d5-4ccd-a8b9-28c03ca91be8
version: 8
creation_date: '2020-01-19'
modification_date: '2026-05-13'
author: Rico Valdez, Dean Luxton, Bhavin Patel, Splunk
status: production
type: TTP
description: |
    The following analytic identifies ICMP traffic to external IP addresses with total bytes (sum of bytes in and bytes out) greater than 1,000 bytes.
    It leverages the Network_Traffic data model to detect large ICMP packet that aren't blocked and are directed toward external networks. We use All_Traffic.bytes in the detection to capture variations in inbound versus outbound traffic sizes, as significant discrepancies or unusually large ICMP exchanges can indicate information smuggling, covert communication, or command-and-control (C2) activities.
    If validated as malicious, this could signal ICMP tunneling, unauthorized data transfer, or compromised endpoints requiring immediate investigation.
data_source:
    - Palo Alto Network Traffic
    - Cisco Secure Access Firewall
search: |-
    | tstats `security_content_summariesonly`
              count earliest(_time) as firstTime
                    latest(_time) as lastTime
                    values(All_Traffic.action) as action
    from datamodel=Network_Traffic where
    All_Traffic.bytes > 1000
    All_Traffic.action != blocked
    AND
    (
        All_Traffic.protocol=icmp
        OR
        All_Traffic.transport=icmp
    )
    NOT ( All_Traffic.dest_ip IN `non_public_ip_blocks`
    OR All_Traffic.dest IN `non_public_ip_blocks`
    )
    by All_Traffic.src_ip All_Traffic.src All_Traffic.dest_ip All_Traffic.dest All_Traffic.protocol
       All_Traffic.bytes All_Traffic.app All_Traffic.bytes_in
       All_Traffic.bytes_out All_Traffic.dest_port All_Traffic.dvc
       All_Traffic.protocol_version All_Traffic.src_port
       All_Traffic.user All_Traffic.vendor_product
    | `drop_dm_object_name("All_Traffic")`
    | eval dest_ip = dest
    | eval src_ip = src
    | iplocation dest_ip
    | `security_content_ctime(firstTime)`
    | `security_content_ctime(lastTime)`
    | `detect_large_icmp_traffic_filter`
how_to_implement: |
    The following analytic was developed with Palo Alto traffic logs. Ensure that the logs are being ingested into Splunk and mapped to the Network_Traffic data model. Use the Splunk Common Information Model (CIM) to normalize the field names and speed up the data modeling process.
known_false_positives: |
    ICMP packets are used in a variety of ways to help troubleshoot networking issues and ensure the proper flow of traffic. As such, it is possible that a large ICMP packet could be perfectly legitimate. If large ICMP packets are associated with Command And Control traffic, there will typically be a large number of these packets observed over time. If the search is providing a large number of false positives, you can modify the macro `detect_large_icmp_traffic_filter` to adjust the byte threshold or add specific IP addresses to an allow list.
references: []
drilldown_searches:
    - name: View the detection results for - "$src_ip$" and "$dest_ip$"
      search: '%original_detection_search% | search  src_ip = "$src_ip$" dest_ip = "$dest_ip$"'
      earliest_offset: $info_min_time$
      latest_offset: $info_max_time$
    - name: View risk events for the last 7 days for - "$src_ip$" and "$dest_ip$"
      search: '| from datamodel Risk.All_Risk | search normalized_risk_object IN ("$src_ip$", "$dest_ip$") | 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"
finding:
    title: Large ICMP traffic greater than a 1000 bytes detected from $src_ip$ to $dest_ip$
    entity:
        field: src_ip
        type: system
        score: 50
intermediate_findings:
    entities:
        - field: dest_ip
          type: system
          score: 50
          message: Large ICMP traffic greater than a 1000 bytes detected from $src_ip$ to $dest_ip$
analytic_story:
    - Command And Control
    - China-Nexus Threat Activity
    - Backdoor Pingpong
    - Cisco Secure Access Analytics
asset_type: Endpoint
mitre_attack_id:
    - T1095
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/attack_techniques/T1095/palologs/large_icmp.log
          sourcetype: pan:traffic
          source: not_applicable
      test_type: unit
    - name: Cisco Secure Access Firewall True Positive Test
      attack_data:
        - data: https://media.githubusercontent.com/media/splunk/attack_data/master/datasets/cisco_secure_access/firewall/large_icmp.log
          source: cisco_cloud_security_addon
          sourcetype: cisco:cloud_security:firewall
      test_type: unit

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