Hi SAM_2023,
That's a really good point and question, you can actually disable the clientless connection by running one of this options:
1- Keepout
config t
webvpn
keepout "message"
2- Portal Access deny
config t
webvpn
portal-access-rule 1 deny any
8About the possible brute force i will recommend you to configure a vpn-simultaneous login 0 in your default group policy, just keep in mind you need to configure a vpn-simultaneous login 3* manually in all your other group policies:
config
group-policy DfltGrpPolicy attributes
vpn-simultaneous-logins 0
*vpn-simultaneous login 3 is the default value.
Hope this helps!
-JP-