Invalid TCP Flags: High Intensity

Rule ID

PH_Rule_Flow_207

Default Status

Enabled

Description

Detects 500 or more flows in 5 minutes, with invalid TCP flag combinations (FIN, SYN-FIN, SYN-FIN-PUSH, SYN-FIN-RESET, SYN-FIN-RESET-PUSH,SYN-FIN-RESET-PUSH-ACK-URG) - may indcate scanning and probing activity from the sender

Severity

MITRE ATT&CK® Tactics

Discovery

Discovery consists of techniques an adversary may use to gain knowledge about the system and internal network. These techniques help adversaries observe the environment and orient themselves before deciding how to act. They also allow adversaries to explore what they can control and what’s around their entry point in order to discover how it could benefit their current objective. Native operating system tools are often used toward this post-compromise information-gathering objective.

https://attack.mitre.org/tactics/TA0007

MITRE ATT&CK® Techniques

No Technique Specified

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.

InvalidTCPFlag

SubPattern Definitions

SubPattern Name: InvalidTCPFlag

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 = 6 AND srcDestTCPFlags IN (1,3,7,11,15,31,63) AND eventType IN (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

Aggregate Constraint

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

COUNT(*) >= 500

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 = InvalidTCPFlag.srcIpAddr,
incidentCount = InvalidTCPFlag.COUNT(*)

FortiSIEM Rules