Downgrade from 7.2.6 to 6.4.6

[TimeCop79]

Hi,

Is it possible to downgrade my FGT 40F from version 7.2.6 to 6.4.6 directly and without any issues?

Thanks 

[Toshi_Esumi]

Probably not practical unless you have a backup config of 6.4.6 to upload (which hasn't changed much) after flushing&uploading the 6.4.6 image to the flash memory.

Why do you want/need to downgrade whatever your model of the FGT?

Toshi

[TimeCop79]

Yes I have already a backup, I want this downgrade because all my devices are on fortios 6 even my forti manager

[Toshi_Esumi · Accepted solution]

At least I can suggest you upgrade the 6.4.6 to 6.4.15 after the downgrade is done to avoid major vulnerabilities like this:
https://www.fortiguard.com/psirt/FG-IR-23-460

Toshi

[adimailig]

Here is the guidelines/best practice for Fortigate Downgrade.
https://community.fortinet.com/t5/FortiGate/Technical-Tip-Best-Practices-for-firmware-upgrades-and/t...

[TimeCop79]

Thank you

[TimeCop79]

BTW,  When I perform the downgrade, the Fortigate freezes during startup, and I have to change the security level from 2 to 1 to resolve the problem.

[adimailig]

Hi @TimeCop79 

It seems that your bios version 5000100 or 6000100 (or newer). 
For this bios when downgrading changing the security level is needed to avoid issue.

You may refer to below documentation.

https://community.fortinet.com/t5/FortiGate/Troubleshooting-Tip-Downgrade-of-FortiOS-fails-due-to-BI...