Provided by: sslh_1.9-1_amd64
sslh - ssl/ssh multiplexer
sslh [ -t num ] [-p listening address [-p listening address ...] [-l target address for SSL] [-s target address for SSH] [-o target address for OpenVPN] [-u username] [-P pidfile] [-v] [-i] [-V] [-f] [-n]
sslh accepts HTTPS, SSH and OpenVPN connections on the same port. This makes it possible to connect to an SSH server or an OpenVPN on port 443 (e.g. from inside a corporate firewall, which almost never block port 443) while still serving HTTPS on that port. The idea is to have sslh listen to the external 443 port, accept the incoming connections, work out what type of connection it is, and then fordward to the appropriate server. Protocol detection The protocol detection is made based on the first bytes sent by the client: SSH connections start by identifying each other's versions using clear text "SSH-2.0" strings (or equivalent version strings). This is defined in RFC4253, 4.2. Meanwhile, OpenVPN clients start with 0x00 0x0D 0x38. Additionally, two kind of SSH clients exist: the client waits for the server to send its version string ("Shy" client, which is the case of OpenSSH and Putty), or the client sends its version first ("Bold" client, which is the case of Bitvise Tunnelier and ConnectBot). sslh waits for some time for the incoming connection to send data. If it stays quiet after the timeout period, it is assumed to be a shy SSH client, and is connected to the SSH server. Otherwise, sslh reads the first packet the client provides, and connects it to the SSH server if it starts with "SSH-", or connects it to the SSL server otherwise. Libwrap support One drawback of sslh is that the ssh and httpd servers do not see the original IP address of the client anymore, as the connection is forwarded through sslh. sslh provides enough logging to circumvent that problem. However it is common to limit access to ssh using libwrap or tcpd. For this reason, sslh can be compiled to check SSH accesses against SSH access lists as defined in /etc/hosts.allow and /etc/hosts.deny.
-t num, --timeout num Timeout before a connection is considered to be SSH. Default is 2s. -p listening address, --listen listening address Interface and port on which to listen, e.g. foobar:443, where foobar is the name of an interface (typically the IP address on which the Internet connection ends up). This can be specified several times to bind sslh to several addresses. --ssl target address Interface and port on which to forward SSL connection, typically localhost:443. Note that you can set sslh to listen on ext_ip:443 and httpd to listen on localhost:443: this allows clients inside your network to just connect directly to httpd. --ssh target address Interface and port on which to forward SSH connections, typically localhost:22. --openvpn target address Interface and port on which to forward OpenVPN connections, typically localhost:1194. --tinc target address Interface and port on which to forward tinc connections, typically localhost:655. This is experimental. If you use this feature, please report the results (even if it works!) -v, --verbose Increase verboseness. -n, --numeric Do not attempt to resolve hostnames: logs will contain IP addresses. This is mostly useful if the system's DNS is slow and running the sslh-select variant, as DNS requests will hang all connections. -V Prints sslh version. -u username, --user username Requires to run under the specified username. Defaults to nobody (which is not perfect -- ideally sslh should run under its own UID). -P pidfile, --pid-file pidfile Specifies the file in which to write the PID of the main server. Defaults to /var/run/sslh.pid. -i, --inetd Runs as an inetd server. Options -P (PID file), -p (listen address), -u (user) are ignored. -f, --foreground Runs in foreground. The server will not fork and will remain connected to the terminal. Messages normally sent to syslog will also be sent to stderr.
/etc/init.d/sslh Start-up script. The standard actions start, stop and restart are supported. /etc/default/sslh Server configuration. These are environment variables loaded by the start-up script and passed to sslh as command-line arguments. Refer to the OPTIONS section for a detailed explanation of the variables used by sslh.
Last version available from <http://www.rutschle.net/tech/sslh>, and can be tracked from <http://freshmeat.net/projects/sslh/>.
Written by Yves Rutschle