The SSH tunnel-operator's debug statements look similar ~]# debug1: Connection to port 9998 forwarding to socks port 0 requested.ĭebug2: channel 3: decode socks4: user /0ĭebug2: channel 3: decode socks4a: host stor/4ĭebug2: channel 3: dynamic request: socks4 host stor port 22 command 1 On a working Fedora 33 system the SSH tunnel-user client connects and can send traffic through the tunnel. If the SSH to bastion (tunnel-operator) has verbose debugging enabled, It will report 'open confirm' indicating a client attempting to use the tunnel:ĭebug2: channel 3: open confirm rwindow 2097152 rmax 32768īut *immediately* afterwards, the SSH tunnel-operator reports it is closing its side of the connection: Kex_exchange_identification: Connection closed by remote host With verbose debugging enabled, the SSH client attempting to use the tunnel (tunnel-user) will process its config file (if exists), announce the Local version string, then *immediately* report that the connection has been closed:ĭebug1: Local version string SSH-2.0-OpenSSH_8.7 $ ssh -vvv -o 'Prox圜ommand=ncat -proxy-type="socks4" -proxy localhost:9998 %h %p' results: * The SSH client will execute ncat to proxy SSH through the tunnel to the remote target. Attempt to create an SSH connection between the client workstation and the private node. Leave this session running as it just maintains the tunnel.ģ. $ ssh -vvv -l username -p 22 -D 9998 bastion-node.domain Establish a primary connection with the bastion and create the tunnel. The ISO provides OpenSSH and nmap-ncat by default with no third-party repos required.Ģ. Use the Fedora 35 Workstation ISO to do a basic install of Fedora 35. You will need three nodes: A Fedora 35 workstation client, a bastion host and a third 'private' host to attempt to access via a tunnel through the bastion.ġ. I can consistently reproduce this with a clean Fedora 35 install using only the files provided on the Fedora 35 release ISO. Version-Release number of selected component (if applicable): I've tested the same commands to work on Fedora 33 and Fedora 34 out of the box without issue. ![]() This appears to be something broken between nmap-ncat and OpenSSH in the Fedora 35 release. Other clients can successfully use the tunnel including Firefox with the FoxyProxy extension and curl using the proxychains utility to proxy curl traffic through the tunnel. In Fedora 35, the command shown above that uses the ncat command to create a proxy from SSH to the tunnel will fail. TCP clients can then send traffic through localhost:9998 to tunnel traffic through the bastion to the bastion's private network resources. $ ssh -o 'Prox圜ommand=ncat -proxy-type="socks4" -proxy localhost:9998 %h %p' -įirst, a primary SSH connection is made to a bastion and the DynamicForward (-D) feature is used to start a tunnel listening on a specific port (ex:9998) on the client. Specifically, this command fails in Fedora 35 but works in Fedora 33/34 and other *nix systems: ![]() SSH debug output for Fedora 33 client to bastion (Successful Example)įedora 33 Client to bastion creating tunnel output (success)įedora 33 Client through tunnel to private node (success)įedora 35 Client to bastion creating tunnel output (Bug scenario)įedora 35 Client through tunnel to private node (Bug scenario, Failure)įedora 35 is unable to tunnel SSH sessions through an SSH bastion connection using a reliable method promoted by the *nix community that has worked until Fedora 35.
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