issues with ssh access from macos/ linux

[nevolex]

Hi folks I am having issues with access via ssh from macos/ linux pcs

pc ~ % ssh admin@10.10.10.1                                                                                                                                         

Unable to negotiate with 10.10.10.1 port 22: no matching host key type found. Their offer: ssh-rsa                                                                          

I can access it using this modified command:   

ssh -oHostKeyAlgorithms=+ssh-rsa admin@10.10.10.1

I have added these options to ssh profile, restarted ssh server/ rebooted as well for testing, but still getting same results 

Unable to negotiate with 10.10.10.1 port 22: no matching host key type found. Their offer: ssh-rs

Does anyone know what needs to be configured on the palo alto to resolve ssh compatibility issues?

thank you

[JayGolf]

Hi @nevolex ,

Is this a VM-Series FW hosted in the public cloud? 

[TorokAdam]

Did you select the SSH Service Profile you just made on Device\Setup\Management\SSH Management Profile Settings? And then restart the ssh server. (it will tell you to do so after commit)

I've just made the same setting for the same reason and missed this step. 

[akuzhuppilly]

Hello,

For a successful ssh connection at least one mutually-supported choice for each parameter, OpenSSH considers SSH-RSA as a weak algorithm and it has been deprecated since OpenSSH 8.8, it is still supported but disabled by default.
Can you try to connect to the FW by adding the following to your command line: -oHostKeyAlgorithms=+ssh-rsa  

Eg;
ssh -oHostKeyAlgorithms=+ssh-rsa username@x.x.x.x

[pgfarvour]

This is a problem for us as well. Is there a way to have the PA appliance generate keys using SHA2+? I've tried setting the server profile to use ECDSA 256+ and the connection still fails,.. likely because the SSH server is still trying to present the RSA version... I would have expected this to use ECDSA only, and not try and present ssh-rsa keys to the client... eg.

debug2: reserved 0
debug1: kex: algorithm: ecdh-sha2-nistp384
debug1: kex: host key algorithm: (no match)
Unable to negotiate with <redacted> port 22: no matching host key type found. Their offer: ssh-rsa

ssh {
profiles {
mgmt-profiles {
server-profiles {
default_high_security {
ciphers [ aes256-cbc aes256-gcm aes256-ctr];
kex [ ecdh-sha2-nistp384 ecdh-sha2-nistp521];
mac [ hmac-sha2-256 hmac-sha2-512];
session-rekey {
data default;
interval default;
packets default;
}
default-hostkey {
key-type {
ECDSA 384;
}
}
}
}
}
}
regenerate-hostkeys {
mgmt {
key-type {
ECDSA {
key-length 256;
}
}
}
}
mgmt {
server-profile default_high_security;
}
}
[edit deviceconfig system ssh]

[DGutierrez]

This worked. Thank you!

[mghazzi]

This changed in PanOS 10.2 and higher, you can verify using "nmap --script ssh2-enum-algos -sV -p 22 192.168.1.1" you will find that:

PanOS 10.1 had

|   server_host_key_algorithms: (3)

|       ssh-rsa

|       rsa-sha2-512

|       rsa-sha2-256

But PanOS 10.2 only has

|   server_host_key_algorithms: (1)

|       ssh-rsa

you need to tell your ssh client to use the larger key size algorithm

The temporary fix is to use:

ssh -oHostKeyAlgorithms=+ssh-rsa admin@192.168.1.1

While the permanent fix is to:

EITHER

1) Create a Shell alias like this that modifies the command ssh and adds support for ssh-rsa host key algorithm evreytime you run ssh

alias ssh='ssh -oHostKeyAlgorithms=+ssh-rsa'

OR

2) modify your SSH Config File (requires sudo) to add support for ssh-rsa host key algorithm 

sudo nano ~/.ssh/config

and then add the line

HostKeyAlgorithms +ssh-rsa

[mghazzi]

adjusting the HOSTKEY to ALL doesn't help, because ALL=ECDSA or RSA, but the only RSA Hostkey Algorithms in PanOS 10.2 and higher are RSA 2048, 3072, or 4096 (known as ssh-rsa) The only way to connect is to tell the SSH client to step up to rsa 2048 or more, or go with ECDSA.