sshttp - hiding a SSH server behind a HTTP server ================================================= In case your FW policy forbids SSH access to the DMZ or internal network from outside, but you still want to use SSH on machines which only have one open port, e.g. HTTP, you can use "sshttpd". sshttp can multiplex the following protocol pairs: - SSH/HTTP - SSH/HTTPS - SSH/SMTP (without SMTP multiline banners) sshttpd is an easy to use OSI-Layer5 switching daemon. It runs transparently on HTTP port (-L switch, default 80) and decides on incoming connections whether this is SSH or HTTP traffic. If its HTTP traffic it switches the traffic to the HTTP_PORT (-H, default 8080) and if its SSH traffic to SSH_PORT (-S, default 22) respectively. You might need to edit "nf-setup" script to match your ports (22, 80 and 8080 are just fine) and run it to install the proxy rules. Your sshd has to run on $SSH_PORT and your webserver on $HTTP_PORT. Thats basically it. Go ahead and run sshttpd (as root) and it will layer5-switch your traffic destinated to TCP port 80. If you want to mux SMTP with sshttp, just give "25" as -L parameter, "2525" as -H parameter, and setup your smtp daemon to listen on 2525. Then edit the nf-setup script to match these ports. In the Makefile, change the SMTP_DOMAIN and SSH_BANNER to your needs (SSH_BANNER must match exactly yours of the running sshd). SMTP/SSH muxing was tested with OpenSSH client and Postfix client and server. You dont need to patch any of your ssh/web/smtp client or server software. It works as is. sshttpd runs only on Linux and needs IP_TRANSPARENT support. It would work without, but by using IP_TRANSPARENT it is possible to even have unmodified syslogs, e.g. the original source IP/port of incoming connections is passed as-is to the SSH/HTTP/SMTP servers. sshttpd is also a tricky anti-SSH0day (if ever:) and anti SSH-scanning/bruteforcing measurement. sshttpd has small footprint and was optimized for speed so it also runs on heavily loaded web servers. Since version 0.24, sshttpd also supports multiple CPU cores. Unless "-n 1" is used as switch, sshttpd binds one thread per CPU core, to better exploit the hardware if running on heavily used web servers. It still runs this fixed number of threads no matter how many 1000s connection it handles at the same time. sshttpd also runs as user nobody in a chroot now (configurable via -U and -R switch) if compiled with USE_CAPS. It can now also distinguish between SSH and SSL sessions, you just have to use an LOCAL_PORT (-L) of 443 or 4433 and change the HTTP_PORT in the nf-setup script to match your webservers HTTPS port. You cannot mix HTTP/SSH and HTTPS/SSH in one sshttpd instance but you can run two sshttpd's to reach that goal: one on LOCAL_PORT 80 and one on LOCAL_PORT 443. If you want to use the least-privilege feature you need to install libcap and libcap-devel packages. Hints/bug reports beyond RTFM to sebastian.krahmer [at] gmail com.
Commits by Sebastian Krahmer were pushed to piorekf/sshttp
9ae06f6 - - fix typo
5b33fc6 - - typo fixes, better README
3e83d95 - - added SMTP mux support - made protocol decision for ssh/http easier - change STATE_CLOSING timeout to be faster (and again match that in lophttpd, ...
5a7f85f - - changed state engine to match logic of lophttp's frontend ( POLLIN/POLLOUT setting/clearing)
2fc4c21 - - shutdown/cleanup logic is now the same as in lophttpd
e76b8b3 - revert one piece from last commit that made hanging connections last forever due to POLLIN in .revents (pulled plug)
878daf6 - - added STATE_CLOSING to try as best as we can to deliver any pending data to peer, if one peer HUPed connection