FortiGate Next Generation Firewall utilizes purpose-built security processors and threat intelligence security services from FortiGuard labs to deliver top-rated protection and high performance, including encrypted traffic.
Article Id 194430

This article describes how to use IPS custom override.

FortiOS 5.0/6.0

To change the custom IPS signature behaviour are as follows:

1. Go to security profile > Intrusion Prevention > Edit IPS sensor.
2. Go to IPS Signatures > Add Signature.
3. Select Add predefined custom signature.
4. Once Selected right click and change the action as deny.
5. Select OK.

Related Articles

Change Intrusion Protection Sensor Default Action

Intrusion Protection - Using DoS Sensor in FortiOS 4.0