ID | Technique | Tactic |
---|---|---|
T1095 | Non-Application Layer Protocol | Command And Control |
Detection: Detect Large Outbound ICMP Packets
Description
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
3 latest(_time) as lastTime values(All_Traffic.action) as action values(All_Traffic.bytes) as bytes from
4 datamodel=Network_Traffic where All_Traffic.action !=blocked (All_Traffic.protocol=icmp OR All_Traffic.transport=icmp) All_Traffic.bytes
5 > 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.src_ip All_Traffic.dest_ip All_Traffic.protocol
6
7| `drop_dm_object_name("All_Traffic")`
8| iplocation dest_ip
9| `security_content_ctime(firstTime)`
10| `security_content_ctime(lastTime)`
11| `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
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 |
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 | Risk Score | Impact | Confidence |
---|---|---|---|
Detect Large Outbound ICMP Packets detected from $src_ip$ to $dest_ip$ | 25 | 50 | 50 |
Detection Testing
Test Type | Status | Dataset | Source | Sourcetype |
---|---|---|---|---|
Validation | ✅ Passing | 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: 6