mirror of https://github.com/moparisthebest/sslh
157 lines
4.5 KiB
Plaintext
157 lines
4.5 KiB
Plaintext
# I'm just not gonna write troff :-)
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=head1 NAME
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sslh - ssl/ssh multiplexer
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=head1 SYNOPSIS
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sslh [ B<-t> I<num> ] [B<-p> I<listening address>] [B<-l> I<target address for SSL>] [B<-s> I<target address for SSH>] [B<-o> I<target address for OpenVPN>] [B<-u> I<username>] [B<-P> I<pidfile>] [-v] [-i] [-V] [-f]
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=head1 DESCRIPTION
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B<sslh> accepts HTTPS, SSH and OpenVPN connections on the
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same port. This makes it possible to connect to an SSH
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server or an OpenVPN on port 443 (e.g. from inside a
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corporate firewall, which almost never block port 443) while
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still serving HTTPS on that port.
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The idea is to have B<sslh> listen to the external 443 port,
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accept the incoming connections, work out what type of
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connection it is, and then fordward to the appropriate
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server.
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=head2 Protocol detection
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The protocol detection is made based on the first bytes sent
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by the client: SSH connections start by identifying each
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other's versions using clear text "SSH-2.0" strings (or
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equivalent version strings). This is defined in RFC4253,
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4.2. Meanwhile, OpenVPN clients start with 0x00 0x0D 0x38.
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Additionally, two kind of SSH clients exist: the client
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waits for the server to send its version string ("Shy"
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client, which is the case of OpenSSH and Putty), or the
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client sends its version first ("Bold" client, which is the
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case of Bitvise Tunnelier and ConnectBot).
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B<sslh> waits for some time for the incoming connection to
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send data. If it stays quiet after the timeout period, it is
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assumed to be a shy SSH client, and is connected to the SSH
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server. Otherwise, B<sslh> reads the first packet the client
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provides, and connects it to the SSH server if it starts
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with "SSH-", or connects it to the SSL server otherwise.
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=head2 Libwrap support
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One drawback of B<sslh> is that the B<ssh> and B<httpd>
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servers do not see the original IP address of the client
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anymore, as the connection is forwarded through B<sslh>.
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B<sslh> provides enough logging to circumvent that problem.
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However it is common to limit access to B<ssh> using
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B<libwrap> or B<tcpd>. For this reason, B<sslh> can be
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compiled to check SSH accesses against SSH access lists as
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defined in F</etc/hosts.allow> and F</etc/hosts.deny>.
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=head1 OPTIONS
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=over 4
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=item B<-t> I<num>
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Timeout before a connection is considered to be SSH. Default
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is 2s.
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=item B<-p> I<listening address>
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Interface and port on which to listen, e.g. I<foobar:443>,
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where I<foobar> is the name of an interface (typically the
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IP address on which the Internet connection ends up).
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Defaults to I<0.0.0.0:443> (listen to port 443 on all
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available interfaces).
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=item B<-l> I<target address for SSL>
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Interface and port on which to forward SSL connection,
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typically I<localhost:443>.
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Defaults to I<localhost:443> (this assumes you would
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configure your B<httpd> process to listen to port 443).
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Note that you can set B<sslh> to listen on I<ext_ip:443> and
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B<httpd> to listen on I<localhost:443>: this allows clients
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inside your network to just connect directly to B<httpd>.
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=item B<-s> I<target address for SSH>
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Interface and port on which to forward SSH connection,
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defaults to I<localhost:22>.
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=item B<-o> I<target address for OpenVPN>
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Interface and port on which to forward OpenVPN connections.
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This parameter is optional, and has no default. If not
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specified, incoming OpenVPN connections will not be detected
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as such and treated the same as SSL.
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=item B<-v>
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Increase verboseness.
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=item B<-V>
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Prints B<sslh> version.
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=item B<-u> I<username>
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Requires to run under the specified username. Defaults to
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I<nobody> (which is not perfect -- ideally B<sslh> should
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run under its own UID).
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=item B<-P> I<pidfile>
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Specifies the file in which to write the PID of the main
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server. Defaults to I</var/run/sslh.pid>.
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=item B<-i>
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Runs as an I<inetd> server. Options B<-P> (PID file), B<-p>
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(listen address), B<-u> (user) are ignored.
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=item B<-f>
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Runs in foreground. The server will not fork and will remain connected
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to the terminal. Messages normally sent to B<syslog> will also be sent
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to I<stderr>.
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=back
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=head1 FILES
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=over 4
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=item F</etc/init.d/sslh>
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Start-up script. The standard actions B<start>, B<stop> and
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B<restart> are supported.
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=item F</etc/default/sslh>
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Server configuration. These are environment variables
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loaded by the start-up script and passed to B<sslh> as
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command-line arguments. Refer to the OPTIONS section for a
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detailed explanation of the variables used by B<sslh>.
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=back
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=head1 SEE ALSO
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Last version available from
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L<http://www.rutschle.net/tech/sslh>, and can be tracked
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from L<http://freshmeat.net/projects/sslh/>.
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=head1 AUTHOR
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Written by Yves Rutschle
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