Fortinet FortiOS

FortiOS is an embedded operating system used on various appliances from Fortinet. Depending on the version of FortiOS, not all command may be available, and if major differences are known, they are combined in a specific section.

SSH into an appliance running FortiOS, or use a local serial connection in order to apply these options.

FortiOS >= 7.4.0

Individual FortiOS 7.4.x versions have sometimes introduced changes or added features, they are summarized into a single section referencing only the latest version but are outlined here and recommendations apply to the latest (known) version:

• 7.4.4: Most commands related to SSH have been moved from config system global to config system ssh-config, one subcommand was renamed
• 7.4.2: set ssh-hostkey-algo changed, more configurable SSH host key algorithms became available
• 7.4.1: set ssh-kex-algo changed, more configurable KEX algorithms became available
• 7.4.0: set ssh-hostkey-algo added, it allows configuring one or more SSH host key algorithms

config system global

# These commands shoulnd't change default settings
set admin-ssh-v1 disable
set strong-crypto enable

# These commands do change default settings
set dh-params 8192

end

config system ssh-config

# These commands do change default settings
set ssh-enc-algo [email protected] [email protected]
set ssh-hsk-algo ssh-ed25519
set ssh-kex-algo diffie-hellman-group16-sha512 diffie-hellman-group18-sha512 [email protected]
set ssh-mac-algo [email protected] [email protected]

end

References:

• Fortinet document library: FortiGate / FortiOS 7.4.4 CLI Reference > config system global and config system ssh-config :
  • Commands moved from global to ssh-config: ssh-enc-algo, ssh-kex-algo and ssh-mac-algo
  • Commands moved from global to ssh-config and renamed: ssh-hostkey-algo became ssh-hsk-algo
• Fortinet document library: FortiGate / FortiOS 7.4.2 CLI Reference > config system global:
  • ssh-hostkey-algo allows enabling or disabling 7 HostKeyAlgorithms
• Fortinet document library: FortiGate / FortiOS 7.4.1 CLI Reference > config system global:
  • ssh-hostkey-algo allows enabling or disabling 5 HostKeyAlgorithms
  • ssh-kex-algo allows enabling or disabling 11 KEX algorithms
• Fortinet document library: FortiGate / FortiOS 7.4.0 CLI Reference > CLI reference > config system global:
  • ssh-hostkey-algo becomes available
  • ssh-kex-algo allows enabling or disabling 8 KEX algorithms
• Fortinet document library: FortiGate / FortiOS 7.2.5 CLI Reference > CLI reference > config system global:
  • ssh-hostkey-algo is not available

FortiOS >= 7.0.2 <= 7.4.0

Starting with FortiOS 7.0.2 some ciphers became individually configurable, several options have been renamed compared to previous versions.

config system global

# These commands shoulnd't change default settings
set admin-ssh-v1 disable
set strong-crypto enable

# These commands do change default settings
set dh-params 8192
set ssh-enc-algo [email protected] [email protected]
set ssh-kex-algo [email protected]
set ssh-mac-algo [email protected] [email protected]

end

References

• Fortinet document library: FortiGate / FortiOS 7.0.0 > New Features > Enabling individual ciphers in the SSH administrative access protocol
• Fortinet document library: FortiGate / FortiOS 7.0.2 > CLI reference > config system global:
  • Previous commands like set ssh-kex-sha1 are not available anymore.
  • New commands like set ssh-kex-algo have been introduced.
• Fortinet document library: FortiGate / FortiOS 7.0.1 > CLI reference > config system global:
  • Commands like set ssh-key-sha1 are still available.

FortiOS >= 5.6.0 <= 7.0.1

Starting with FortiOS 5.6 strong-crypto defaults to enable while SSHv1 defaults to disable since at least FortiOS 5.0.

config system global

# These commands shoulnd't change default settings
set admin-ssh-v1 disable
set strong-crypto enable

# These commands do change default settings
set dh-params 8192
set ssh-cbc-cipher disable
set ssh-hmac-md5 disable
set ssh-kex-sha1 disable
set ssh-mac-weak disable

end

References

• Fortinet document library: FortiGate / FortiOS 5.6.0 > CLI Reference: Page 569, strong-crypto defaults to enable
• Fortinet document library: FortiGate / FortiOS 5.4.0 > CLI Reference: Page 163-164, strong-crypto defaults to disable
• Fortinet document library: FortiGate / FortiOS 5.0.0 > CLI Reference: Page 527, admin-ssh-v1 defaults to disable. This is the earliest reference found, newer versions stick to the same default.

Limitations

In most versions of FortiOS the configuration options available don't permit reaching a perfect score, here are some of the reasons:

• Ciphers: Only after FortiOS 7.0.2 certain ciphers can be individually enabled and disabled.
• Host-key algorithms: Only after FortiOS 7.4.1 allows configuring host keys algorithms, therefore rsa-sha2-256 and rsa-sha2-512 cannot be disabled in older releases.

Validated versions

FortiOS	ssh-audit
7.4.1	master @ 02ab487232de438c0811116f2676cb1c9b5f3d62
7.2.5	master @ 02ab487232de438c0811116f2676cb1c9b5f3d62
7.0.12	master @ 02ab487232de438c0811116f2676cb1c9b5f3d62
7.0.11	master @ 02ab487232de438c0811116f2676cb1c9b5f3d62