Getting “Xlib: PuTTY X11 proxy: wrong authentication protocol attempted”? I have the answer :)

Jason L Froebe — Sat, 15 Nov 2008 02:00:57 +0000

Here’s the scenario:

You ssh to a remote server with your login and either sudo or su to another user to run some application that uses a X Windows front end. There is a firewall between your desktop and the remote server that allows only ssh connections (port 22). When you run into the error “Xlib: PuTTY X11 proxy: wrong authentication protocol attempted”. What to do?

ssh jason@remote-server -X
jason $ echo $DISPLAY
localhost:10.0
jason $ su – oracle
oracle‘s Password:
oracle $ xterm
Xlib: connection to "localhost:10.0" refused by server
Xlib: PuTTY X11 proxy: wrong authentication protocol attempted
xterm Xt error: Can’t open display: localhost:10.0

On recent OpenSSH Server releases, you can simply enable “ForwardX11Trusted yes” in the /etc/ssh/sshd_config file and restart the OpenSSH server. If you’re not using a recent OpenSSH Server release or if you can’t for security or political reasons, what could you do? Give up? It’s simpler than you think.
You need to temporarily transfer the authorization to the other account. First, get the key from your account:

jason $ xauth list
aspc2o1/unix:10 MIT-MAGIC-COOKIE-1 bc334c66cfec3c5c3d5b0efc4ee9d3ad

Next, sudo/su to the other account and add the authorization key.

jason $ su – oracle
oracle $ xauth add aspc2o1/unix:10 MIT-MAGIC-COOKIE-1 bc334c66cfec3c5c3d5b0efc4ee9d3ad

Now, you should be able to start any X Windows application, assuming that your DISPLAY variable is set to go through the ssh tunnel:

oracle $ xterm

Jason L. Froebe - Tech tips and How Tos for Fellow Techies » xauth

Getting “Xlib: PuTTY X11 proxy: wrong authentication protocol attempted”? I have the answer :)