[Bug 3503] OpenSSH tries executing banner as command

[bugzilla-daemon at mindrot.org]

https://bugzilla.mindrot.org/show_bug.cgi?id=3503

Darren Tucker <dtucker at dtucker.net> changed:

           What    |Removed                     |Added
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                 CC|                            |dtucker at dtucker.net

--- Comment #1 from Darren Tucker <dtucker at dtucker.net> ---
(In reply to Mateusz from comment #0)
[...]
> As you can see, OpenSSH tries to execute banner version as command.

That's because that's what you configured it to do, although it's not
immediately obvious.

What's happening is that the proxy command is bringing up an
interactive session, then the client tries to initiate an SSH
connection with the proxycommand which is connected to a shell at the
other end.  The client's initial banner is sent over the proxycommand
to the that shell which tries to run it, fails, and returns the error
that you see.

If we strip your example down to the proxycommand you can see this:

$ ssh -o 'ProxyCommand ssh -vvv 127.0.0.1' 127.0.01
[...]
debug2: shell request accepted on channel 0
debug2: channel 0: rcvd ext data 59
-bash: line 1: $'SSH-2.0-OpenSSH_9.0\r': command not found
debug2: channel 0: written 59 to efd 6

It's not clear what exactly you're trying to do, but you probably want
to add a "-W [host]:[port]" to the proxycommand (or use ProxyJump).

> Based on the StackOverflow (link:
> https://unix.stackexchange.com/questions/269024/change-ssh-banner-
> which-is-grabbed-by-netcat) we can modify banner

That's different because it's referring to the banner string sent by
the server side.  In your case the string is sent by the client.

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