FortiSIEM Rules

Unusually Large ICMP Echo Packets

Rule ID

PH_Rule_Flow_10

Default Status

Enabled

Description

Detects large (> 200 bytes/pkt) ICMP echo request and response packets - this is unusual since ICMP packets carry minimal information and are small in size. This may indicate that some other traffic is being carried over ICMP protocol.

Severity

9

Category

Security

MITRE ATT&CK® Tactics

Command And Control

MITRE ATT&CK® Techniques


T1095

Non-Application Layer Protocol

Adversaries may use a non-application layer protocol for communication between host and C2 server or among infected hosts within a network. The list of possible protocols is extensive but Specific examples include use of network layer protocols, such as the Internet Control Message Protocol (ICMP), transport layer protocols, such as the User Datagram Protocol (UDP), session layer protocols, such as Socket Secure (SOCKS), as well as redirected/tunneled protocols, such as Serial over LAN (SOL).

https://attack.mitre.org/techniques/T1095

Impacts

Network

Data Source

FortiGate via Syslog or Netflow, Checkpoint via Syslog or Netflow, Palo Alto via Syslog or Netflow

Detection

Correlation

Remediation Guidance

No remediation guidance specified

Time Window

If the following pattern or patterns match an ingested event within the given time window in seconds, trigger an incident.

300 seconds

Trigger Conditions

If the following defined pattern/s occur within a 300 second time window.

LargeICMPEchoReq AND LargeICMPEchoResp

Global Constraint

This defines how two or more distinct events are related in a time-series based action. e.g. An event occurs followed by another event if the source IP, user, and messageId are the same

LargeICMPEchoReq.srcIpAddr = LargeICMPEchoResp.destIpAddr AND LargeICMPEchoReq.destIpAddr = LargeICMPEchoResp.srcIpAddr

SubPattern Definitions

SubPattern Name: LargeICMPEchoReq

This is the named definition of the event query, this is important if multiple subpatterns are defined to distinguish them.

SubPattern Query

This is the query logic that matches incoming events

ipProto = 1 AND icmpType = 8 AND eventType IN (Group@PH_SYS_EVENT_PermitNetTraffic, Group@PH_SYS_EVENT_NetflowTraffic, Group@PH_SYS_EVENT_BiNetflowTraffic)

Group by Attributes

This defines how matching events are aggregated, only events with the same matching attribute values are grouped into one unique incident ID

srcIpAddr, destIpAddr

Aggregate Constraint

This is most typically a numerical constraint that defines when the rule should trigger an incident

SUM(sentPkts64) > 0 AND SUM(sentBytes64)/SUM(sentPkts64) >= 200
Operator Rank: 0 Operator Type: AND

This operator defines the logic condition relating to the prior event subpattern clause and the following event subpattern clause

SubPattern Name: LargeICMPEchoResp

This is the named definition of the event query, this is important if multiple subpatterns are defined to distinguish them.

SubPattern Query

This is the query logic that matches incoming events

ipProto = 1 AND icmpType = 0 AND eventType IN (Group@PH_SYS_EVENT_PermitNetTraffic, Group@PH_SYS_EVENT_NetflowTraffic, Group@PH_SYS_EVENT_BiNetflowTraffic)

Group by Attributes

This defines how matching events are aggregated, only events with the same matching attribute values are grouped into one unique incident ID

srcIpAddr, destIpAddr

Aggregate Constraint

This is most typically a numerical constraint that defines when the rule should trigger an incident

SUM(sentPkts64) > 0 AND SUM(sentBytes64)/SUM(sentPkts64) >= 200

Incident Attribute Mapping

This section defines which fields in matching raw events should be mapped to the incident attributes in the resulting incident.

The available raw event attributes to map are limited to the group by attributes and the aggregate event constraint fields for each subpattern

 srcIpAddr = LargeICMPEchoReq.srcIpAddr,
 destIpAddr = LargeICMPEchoReq.destIpAddr