Resolve the Security Alert in Putty 0.68 on Cisco ASA firewalls

Not cloud related but useful to some all the same.

With the recent introduction of Putty version 0.68 you may now get the following Security Alert when SSH’ing to Cisco ASA firewalls. See this link for more info on why.


Getting rid of this nag, i.e. improving the security of your firewall, is simple.

Update your crypto general-keys pair to a 2048-bit modulus, and then change the SSH key-exchange group. Here’s the code:

firewall(config)# crypto key generate rsa general-keys modulus 2048
WARNING: You have a RSA keypair already defined named <Default-RSA-Key>.

Do you really want to replace them? [yes/no]: yes
Keypair generation process begin. Please wait...

firewall(config)# ssh key-exchange group dh-group14-sha1