Configuration ============= If you use the scripts provided, sslh will get its configuration from /etc/sslh.cfg. Please refer to example.cfg for an overview of all the settings. A good scheme is to use the external name of the machine in `listen`, and bind `httpd` to `localhost:443` (instead of all binding to all interfaces): that way, HTTPS connections coming from inside your network don't need to go through `sslh`, and `sslh` is only there as a frontal for connections coming from the internet. Note that 'external name' in this context refers to the actual IP address of the machine as seen from your network, i.e. that that is not `127.0.0.1` in the output of `ifconfig(8)`. Libwrap support --------------- Sslh can optionally perform `libwrap` checks for the sshd service: because the connection to `sshd` will be coming locally from `sslh`, `sshd` cannot determine the IP of the client. OpenVPN support --------------- OpenVPN clients connecting to OpenVPN running with `-port-share` reportedly take more than one second between the time the TCP connection is established and the time they send the first data packet. This results in `sslh` with default settings timing out and assuming an SSH connection. To support OpenVPN connections reliably, it is necessary to increase `sslh`'s timeout to 5 seconds. Instead of using OpenVPN's port sharing, it is more reliable to use `sslh`'s `--openvpn` option to get `sslh` to do the port sharing. Using proxytunnel with sslh --------------------------- If you are connecting through a proxy that checks that the outgoing connection really is SSL and rejects SSH, you can encapsulate all your traffic in SSL using `proxytunnel` (this should work with `corkscrew` as well). On the server side you receive the traffic with `stunnel` to decapsulate SSL, then pipe through `sslh` to switch HTTP on one side and SSL on the other. In that case, you end up with something like this: ssh -> proxytunnel -e ----[ssh/ssl]---> stunnel ---[ssh]---> sslh --> sshd Web browser -------------[http/ssl]---> stunnel ---[http]--> sslh --> httpd Configuration goes like this on the server side, using `stunnel3`: stunnel -f -p mycert.pem -d thelonious:443 -l /usr/local/sbin/sslh -- \ sslh -i --http localhost:80 --ssh localhost:22 * stunnel options: * `-f` for foreground/debugging * `-p` for specifying the key and certificate * `-d` for specifying which interface and port we're listening to for incoming connexions * `-l` summons `sslh` in inetd mode. * sslh options: * `-i` for inetd mode * `--http` to forward HTTP connexions to port 80, and SSH connexions to port 22. Capabilities support -------------------- On Linux (only?), you can compile sslh with `USELIBCAP=1` to make use of POSIX capabilities; this will save the required capabilities needed for transparent proxying for unprivileged processes. Alternatively, you may use filesystem capabilities instead of starting sslh as root and asking it to drop privileges. You will need `CAP_NET_BIND_SERVICE` for listening on port 443 and `CAP_NET_RAW` for transparent proxying (see `capabilities(7)`). You can use the `setcap(8)` utility to give these capabilities to the executable: sudo setcap cap_net_bind_service,cap_net_raw+pe sslh-select Then you can run sslh-select as an unpriviledged user, e.g.: sslh-select -p myname:443 --ssh localhost:22 --tls localhost:443 Transparent proxy support ------------------------- Transparent proxying allows the target server to see the original client IP address, i.e. `sslh` becomes invisible. This makes it easier to use the server's logs, and potential IP-based banning ability. Set up can get complicated, so it has its own [document](tproxy.md). Systemd Socket Activation ------------------------- If compiled with `USESYSTEMD` then it is possible to activate the service on demand and avoid running any code as root. In this mode any listen configuration options are ignored and the sockets are passed by systemd to the service. Example socket unit: [Unit] Before=sslh.service [Socket] ListenStream=1.2.3.4:443 ListenStream=5.6.7.8:444 ListenStream=9.10.11.12:445 FreeBind=true [Install] WantedBy=sockets.target Example service unit: [Unit] PartOf=sslh.socket [Service] ExecStart=/usr/sbin/sslh -v -f --ssh 127.0.0.1:22 --tls 127.0.0.1:443 KillMode=process CapabilityBoundingSet=CAP_NET_BIND_SERVICE CAP_NET_RAW PrivateTmp=true PrivateDevices=true ProtectSystem=full ProtectHome=true User=sslh With this setup only the socket needs to be enabled. The sslh service will be started on demand and does not need to run as root to bind the sockets as systemd has already bound and passed them over. If the sslh service is started on its own without the sockets being passed by systemd then it will look to use those defined on the command line or config file as usual. Any number of ListenStreams can be defined in the socket file and systemd will pass them all over to sslh to use as usual. To avoid inconsistency between starting via socket and starting directly via the service Requires=sslh.socket can be added to the service unit to mandate the use of the socket configuration. Rather than overwriting the entire socket file drop in values can be placed in /etc/systemd/system/sslh.socket.d/.conf with additional ListenStream values that will be merged. In addition to the above with manual .socket file configuration there is an optional systemd generator which can be compiled - systemd-sslh-generator This parses the /etc/sslh.cfg (or /etc/sslh/sslh.cfg file if that exists instead) configuration file and dynamically generates a socket file to use. This will also merge with any sslh.socket.d drop in configuration but will be overriden by a /etc/systemd/system/sslh.socket file. To use the generator place it in /usr/lib/systemd/system-generators and then call systemctl daemon-reload after any changes to /etc/sslh.cfg to generate the new dynamic socket unit. Fail2ban -------- If using transparent proxying, just use the standard ssh rules. If you can't or don't want to use transparent proxying, you can set `fail2ban` rules to block repeated ssh connections from an IP address (obviously this depends on the site, there might be legitimate reasons you would get many connections to ssh from the same IP address...) See example files in scripts/fail2ban. UDP --- `sslh` can perform demultiplexing on UDP packets as well. This only works with `sslh-select` (it is not possible to support UDP with a forking model). Specify a listening address and target protocols with `is_udp: true`. `sslh` will wait for incoming UDP packets, run the probes in the usual fashion, and forward packets to the appropriate target. `sslh` will then remember the association between remote host to target server for 60 seconds by default, which can be overriden with `udp_timeout`. This allows to process both single-datagram protocols such as DNS, and connection-based protocols such as QUIC.