FortiSIEM Rules

VNC traffic from Internet

Rule ID


Default Status



Detects VNC from Internet, which is defined as anything outside the Internal network. Please make sure that the Internal network definition is correct to avoid false positives






Lateral Movement

Lateral Movement consists of techniques that adversaries use to enter and control remote systems on a network. Following through on their primary objective often requires exploring the network to find their target and subsequently gaining access to it. Reaching their objective often involves pivoting through multiple systems and accounts to gain. Adversaries might install their own remote access tools to accomplish Lateral Movement or use legitimate credentials with native network and operating system tools, which may be stealthier.

MITRE ATT&CK® Techniques


Remote Services: VNC

Adversaries may use Valid Accounts to remotely control machines using Virtual Network Computing (VNC). The adversary may then perform actions as the logged-on user.


External Remote Services

Adversaries may leverage external-facing remote services to initially access and/or persist within a network. Remote services such as VPNs, Citrix, and other access mechanisms allow users to connect to internal enterprise network resources from external locations. Access to Valid Accounts to use the service is often a requirement, which could be obtained through credential pharming or by obtaining the credentials from users after compromising the enterprise network.


Remote Access Software

An adversary may use legitimate desktop support and remote access software, such as Team Viewer, Go2Assist, LogMein, AmmyyAdmin, etc, to establish an interactive command and control channel to target systems within networks. These services are commonly used as legitimate technical support software, and may be allowed by application control within a target environment.



Data Source

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



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.

600 seconds

Trigger Conditions

If the following defined pattern/s occur within a 600 second time window.


SubPattern Definitions

SubPattern Name: VNC

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

srcIpAddr NOT IN (Group@PH_SYS_NETWORK_ENTERPRISE_INTERNAL_NET) AND destIpAddr IN (Group@PH_SYS_NETWORK_ENTERPRISE_INTERNAL_NET) AND srcIpPort >= 1024 AND ((destIpPort >= 5800 AND destIpPort <= 5820) OR (destIpPort >= 5900 AND destIpPort <= 5920) OR (destIpPort >= 6000 AND destIpPort <= 6020)) 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


Aggregate Constraint

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

COUNT(*) >= 1

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 = VNC.srcIpAddr,
destIpAddr = VNC.destIpAddr