SSHAuto (wodSSH / wodSSH.NET)

by Wojciech Król, Wednesday, February 19, 2020, 11:16 (1737 days ago) @ Jasmine

Hi,

RFC 4253 specifies that an SSH server that supports both 2.0 and prior versions of SSH should identify its proto version as 1.99:

5.1. Old Client, New Server

Server implementations MAY support a configurable compatibility flag
that enables compatibility with old versions. When this flag is on,
the server SHOULD identify its 'protoversion' as "1.99". Clients
using protocol 2.0 MUST be able to identify this as identical to
"2.0". In this mode, the server SHOULD NOT send the Carriage Return
character (ASCII 13) after the identification string.

In the compatibility mode, the server SHOULD NOT send any further
data after sending its identification string until it has received an
identification string from the client. The server can then determine
whether the client is using an old protocol, and can revert to the
old protocol if required. In the compatibility mode, the server MUST
NOT send additional data before the identification string.

When compatibility with old clients is not needed, the server MAY
send its initial key exchange data immediately after the
identification string.

So, as you can see version "1.99" is for Server (not for client), so the correct behavour for the SSH server that is running oleder version (e.g. 1.5) is to drop connection when the client is sending 1.99. Efectively when client reports version as "1.99" it can connect only to a v2 servers