Disable SSH 1.99 version?

jabalv · September 29, 2011, 6:48am

Hello. My security audit reconise SSH 1.99 protocol version allowed.

But in my sshd_config config is only:

SSH version:

How can I disable support for ssh protocol 1.99 version?

fpmurphy · September 29, 2011, 10:20am

See RFC 4253 Section 5.1

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.