Detection: Detect Large Outbound ICMP Packets

DEPRECATED DETECTION

This detection has been marked as deprecated by the Splunk Threat Research team. This means that it will no longer be maintained or supported. If you have any questions or concerns, please reach out to us at research@splunk.com.

Updated Date: 2025-03-27 ID: e9c102de-4d43-42a7-b1c8-8062ea297419 Author: Rico Valdez, Dean Luxton, Bhavin Patel, Splunk Type: TTP Product: Splunk Enterprise Security

Description

This analytic has been deprecated in favour of a better named detection - Detect Large ICMP Traffic. The following analytic identifies outbound ICMP packets with a size larger than 1,000 bytes. It leverages the Network_Traffic data model to detect unusually large ICMP packets that are not blocked and are destined for external IP addresses. This activity is significant because threat actors often use ICMP for command and control communication, and large ICMP packets can indicate data exfiltration or other malicious activities. If confirmed malicious, this could allow attackers to maintain covert communication channels, exfiltrate sensitive data, or further compromise the network.

Search

1
2| tstats `security_content_summariesonly` count earliest(_time) as firstTime latest(_time) as lastTime values(All_Traffic.action) as action values(All_Traffic.bytes) as bytes from datamodel=Network_Traffic where All_Traffic.action !=blocked (All_Traffic.protocol=icmp OR All_Traffic.transport=icmp) All_Traffic.bytes > 1000 AND NOT All_Traffic.dest_ip IN ("10.0.0.0/8","172.16.0.0/12","192.168.0.0/16") by All_Traffic.action All_Traffic.app All_Traffic.bytes All_Traffic.bytes_in All_Traffic.bytes_out All_Traffic.dest All_Traffic.dest_ip All_Traffic.dest_port All_Traffic.dvc All_Traffic.protocol All_Traffic.protocol_version All_Traffic.src All_Traffic.src_ip All_Traffic.src_port All_Traffic.transport All_Traffic.user All_Traffic.vendor_product 
3| `drop_dm_object_name("All_Traffic")` 
4| `security_content_ctime(firstTime)` 
5| `security_content_ctime(lastTime)` 
6| iplocation dest_ip 
7| `detect_large_outbound_icmp_packets_filter`

Data Source

Name	Platform	Sourcetype	Source
Palo Alto Network Traffic	Network	`'pan:traffic'`	`'screenconnect_palo_traffic'`

Macros Used

Name	Value
security_content_ctime	`convert timeformat="%Y-%m-%dT%H:%M:%S" ctime($field$)`
detect_large_outbound_icmp_packets_filter	`search *`

detect_large_outbound_icmp_packets_filter is an empty macro by default. It allows the user to filter out any results (false positives) without editing the SPL.

Annotations

- MITRE ATT&CK

+ Kill Chain Phases

+ NIST

+ CIS

- Threat Actors

ID	Technique	Tactic
T1095	Non-Application Layer Protocol	Command And Control

Command and Control

DE.CM

CIS 13

Default Configuration

This detection is configured by default in Splunk Enterprise Security to run with the following settings:

Setting	Value
Disabled	true
Cron Schedule	`0 * * * *`
Earliest Time	`-70m@m`
Latest Time	`-10m@m`
Schedule Window	`auto`
Creates Notable	Yes
Rule Title	`%name%`
Rule Description	`%description%`
Notable Event Fields	user, dest
Creates Risk Event	True

This configuration file applies to all detections of type TTP. These detections will use Risk Based Alerting and generate Notable Events.

Implementation

In order to run this search effectively, we highly recommend that you leverage the Assets and Identity framework. It is important that you have a good understanding of how your network segments are designed and that you are able to distinguish internal from external address space. Add a category named internal to the CIDRs that host the company's assets in the assets_by_cidr.csv lookup file, which is located in $SPLUNK_HOME/etc/apps/SA-IdentityManagement/lookups/. More information on updating this lookup can be found here: https://docs.splunk.com/Documentation/ES/5.0.0/Admin/Addassetandidentitydata. This search also requires you to be ingesting your network traffic and populating the Network_Traffic data model

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_outbound_icmp_packets_filter to adjust the byte threshold or add specific IP addresses to an allow list.

Associated Analytic Story

Risk Based Analytics (RBA)

Risk Message:

Detect Large Outbound ICMP Packets detected from $src_ip$ to $dest_ip$

Risk Object	Risk Object Type	Risk Score	Threat Objects
dest_ip	system	25	No Threat Objects
src_ip	system	25	No Threat Objects

Detection Testing

Test Type	Status	Dataset	Source	Sourcetype
Validation	Not Applicable	N/A	N/A	N/A
Unit	✅ Passing	Dataset	`pan:traffic`	`pan:traffic`
Integration	✅ Passing	Dataset	`pan:traffic`	`pan:traffic`

Replay any dataset to Splunk Enterprise by using our replay.py tool or the UI. Alternatively you can replay a dataset into a Splunk Attack Range

Source: GitHub | Version: 11