// Examples for using socat (and filan) //"$" means normal user, "#" requires privileges, "//" starts a comment /////////////////////////////////////////////////////////////////////////////// // similar to netcat // connect to on port 80 and relay to and from stdio $ socat - TCP: # similar to "netcat 80" // listen on port 25, wait for an incoming connection, use CR+NL on this // connection, relay data to and from stdio; // then emulate a mailserver by hand :-) # socat - TCP-LISTEN:25,crlf // listen on port 25, wait for an incoming connection, use CR+NL on this // connection, relay data to and from stdio, but have line editing and history; // then emulate a mailserver by hand :-) # socat readline TCP-LISTEN:25,crlf // provide a transient history enabled front end to stupid line based // interactive programs $ socat readline exec:"nslookup",pty,ctty,setsid,echo=0 // same works for ftp (but password is not hidden) // you may also use a file based history list $ socat readline,history=.nslookup_hist exec:"nslookup",pty,ctty,setsid,echo=0 // using ~ as abbreviation for $HOME does not work! // poor mans 'telnetd' replacement # socat tcp-l:2023,reuseaddr,fork exec:/bin/login,pty,setsid,setpgid,stderr,ctty // and here an appropriate client: $ socat -,raw,echo=0 tcp: // use ssl with client and server certificate for improved security; // replace /bin/login by /bin/bash when using SSL client authentication, can be // run without root then // this is a cool trick, proposed by Christophe Lohr, to dump communications to // two files; it would also work for other manipulations (recode, compress...) // and it might also work with netcat ;-) $ socat TCP-LISTEN:5555 SYSTEM:'tee l2r | socat - "TCP:remote:5555" | tee r2l' /////////////////////////////////////////////////////////////////////////////// // emergence solution because usleep(1) is not always available // this will "sleep" for 0.1s $ socat -T 0.1 pipe pipe /////////////////////////////////////////////////////////////////////////////// // a very primitive HTTP/1.0 echo server (problems: sends reply headers before // request; hangs if client does not shutdown - HTTP keep-alive) // wait for a connection on port 8000; do not wait for request, but immediately // start a shell that sends reply headers and an empty line; then echo all // incoming data back to client $ socat TCP-LISTEN:8000,crlf SYSTEM:"echo HTTP/1.0 200; echo Content-Type\: text/plain; echo; cat" // a less primitive HTTP echo server that sends back not only the reqest but // also server and client address and port. Might have portability issues with // echo ./socat -T 1 -d -d tcp-l:10081,reuseaddr,fork,crlf system:"echo -e \"\\\"HTTP/1.0 200 OK\\\nDocumentType: text/html\\\n\\\ndate: \$\(date\)
\\\"\"; cat; echo -e \"\\\"\\\n
\\\"\"" /////////////////////////////////////////////////////////////////////////////// // for communicating with an attached modem, I had reasonable results with // following command line. Required privileges depend on device mode. // after leaving socat, type "sane". // replace /dev/ttyS0 by the correct serial line or with /dev/modem $ socat readline /dev/ttyS0,raw,echo=0,crlf // or $ socat readline /dev/ttyS0,raw,echo=0,crlf,nonblock // then enter "at$" /////////////////////////////////////////////////////////////////////////////// // relay TCP port 80 from everywhere (internet, intranet, dmz) through your // firewall to your DMZ webserver (like plug-gw) // listen on port 80; whenever a connection is made, fork a new process (parent // process keeps accepting connections), su to nobody, and connect to // www.dmz.mydomain.org on port 80. // attention: this is a substitute for a reverse proxy without providing // application level security. # socat TCP-LISTEN:80,reuseaddr,fork,su=nobody TCP:www.dmz.mydomain.org:80 // Note: parent process keeps running as root, su after forking /////////////////////////////////////////////////////////////////////////////// // relay mail from your DMZ server through your firewall. // accept connections only on dmz interface and allow connections only from // smtp.dmz.mydomain.org. // the advantages over plug-gw and other relays are: // * you can bind to an IP address (even an alias), therefore enhance security // * in your OS you can create several IP aliases and bind another socat daemon // to each, making several application servers addressable // * lots of options, like switching user, chroot, IP performance tuning // * no need for inetd # socat -lm -d -d TCP-LISTEN:25,bind=fw.dmz.mydomain.org,fork,su=nobody,range=smtp.dmz.mydomain.org/32 TCP:smtp.intra.mydomain.org:25 /////////////////////////////////////////////////////////////////////////////// // convert line terminator in ascii streams, stdin to stdout // use unidirectional mode, convert nl to crnl $ socat -u - -,crlf // or cr to nl $ socat -u -,cr - // save piped data similar to 'tee': // copies stdin to stdout, but writes everything to the file too $ socat -,echo=0 open:/tmp/myfile,create,trunc,ignoreeof!!/tmp/myfile /////////////////////////////////////////////////////////////////////////////// // intrusion testing // found an XWindow Server behind IP filters with FTP data hole? (you are // lucky!) // prepare your host: # rm -f /tmp/.X11-unix/X1 // relay a pseudo display :1 on your machine to victim:0 # socat UNIX-LISTEN:/tmp/.X11-unix/X1,fork TCP:host.victim.org:6000,sp=20 & // and try to take a screendump (must be very lucky - when server has not even // host based authentication!) # xwd -root -display :1 -silent >victim.xwd // you sit behind a socks firewall that has IP filters but lazily allows socks // connections to loopback and has only host based X11 security. // like above, but from your inside client: # socat UNIX-LISTEN:/tmp/.X11-unix/X1,fork SOCKS4:firewall:loopback:6000 // or for the HTTP proxy: # socat UNIX-LISTEN:/tmp/.X11-unix/X1,fork PROXY:firewall:loopback:6000 /////////////////////////////////////////////////////////////////////////////// // forms of stdin with stdout, all equivalent $ socat echo - $ socat echo STDIO $ socat echo STDIN!!STDOUT $ socat echo STDIO!!STDIO $ socat echo -!!- $ socat echo FD:0!!FD:1 $ socat echo 0!!1 $ socat echo /dev/stdin!!/dev/stdout // if your OS provides these /////////////////////////////////////////////////////////////////////////////// // some echo address examples $ socat - PIPE $ socat - PIPE:/tmp/pipi // other version of echo $ socat - PIPE:/tmp/pipi,nonblock!!/tmp/pipi // other version of echo $ socat - EXEC:/bin/cat // another echo $ socat - SYSTEM:/bin/cat // another echo $ socat - TCP:loopback:7 // if inetd echo/TCP service activated $ socat - UDP:loopback:7 // if inetd echo/UDP service activated $ socat - /tmp/hugo,trunc,ignoreeof!!/tmp/hugo // with delay $ socat - UDP:loopback:2000,bind=:2000 // self "connection" $ socat - TCP:loopback:2000,bind=:2000 // Linux bug? # socat - IP:loopback:222 // raw protocol, self "connected" (attention, // Linux might drop packets with less than 8 bytes payload) /////////////////////////////////////////////////////////////////////////////// // unidirectional data transfer $ socat -u - - // like "tail -f", but start with showing all file contents $ socat -u FILE:/var/log/syslog.debug,ignoreeof - // like "tail -f", but do not show existing file contents $ socat -u FILE:/var/log/syslog.debug,ignoreeof,seek-end - // write to new file, create with given permission and group (must be member) - race condition with group!!! $ socat -u - CREATE:/tmp/outfile1,group=floppy,perm=0640 // // for an existing file /tmp/outfile1 # socat -u - FILE:/tmp/outfile1,group=floppy,perm=0700,user=4321 /////////////////////////////////////////////////////////////////////////////// // file handling $ socat - FILE:/tmp/outfile1,ignoreeof!!FILE:/tmp/outfile1,append // prints outfile1, then echoes input and protocols into file (appends to old data) /////////////////////////////////////////////////////////////////////////////// // unix socket handling // create a listening unix socket $ rm -f /tmp/mysocket; socat UNIX-LISTEN:/tmp/mysocket - // from another terminal, connect to this socket $ socat UNIX:/tmp/mysocket - // then transfer data bidirectionally /////////////////////////////////////////////////////////////////////////////// // transport examples // socks relay (externally socksify applications); // your ssh client and OS are not socksified, but you want to pass a socks // server with ssh: $ socat TCP-LISTEN:10022,fork SOCKS4:socks.mydomain.org:ssh-serv:22 $ ssh -p 10022 loopback // or better define a ProxyCommand in ~/.ssh/config: ProxyCommand socat - SOCKS:socks.mydomain.org:%h:%p // and with proxy: ProxyCommand socat - PROXY:proxy.mydomain.org:%h:%p,proxyport=8000 /////////////////////////////////////////////////////////////////////////////// // application examples // run sendmail daemon with your favorite network options # socat TCP-LISTEN:25,fork,ip-ttl=4,ip-tos=7,tcp-maxseg=576 EXEC:"/usr/sbin/sendmail -bs",nofork // local mail delivery over UNIX socket - no SUID program required # socat UNIX-LISTEN:/tmp/postoffice,fork,perm-early=0666 EXEC:"/usr/sbin/sendmail -bs" $ socat - /tmp/postoffice /////////////////////////////////////////////////////////////////////////////// // uses of filan // see what your operating system opens for you $ filan // or if that was too detailled $ filan -s // see what file descriptors are passed via exec function $ socat - EXEC:filan,nofork $ socat - EXEC:filan $ socat - EXEC:filan,pipes,stderr $ socat - EXEC:filan,pipes $ socat - EXEC:filan,pty // see what's done by your shell and with option "pipes" $ socat - SYSTEM:filan,pipes // see if gdb gives you an equivalent environment or opens some files for your program $ gdb ./filan (gdb) r (gdb) r -s /////////////////////////////////////////////////////////////////////////////// // want to use chat from the ppp package? // note: some OS's do not need "-e" for echo to print control characters // note: chat might send bytes one by one // with AIX, a similar program is available under the name "pppdial" $ socat -d -d tcp:localhost:25,crlf,nodelay exec:'/usr/sbin/chat -v -s "\"220 \"" "\"HELO loopback\"" "\"250 \"" "\"MAIL FROM: \"" "\"250 \"" "\"RCPT TO: root\"" "\"250 \"" "\"DATA\"" "\"354 \"" "\"test1'$(echo -e "\r.")'\"" "\"250 \"" "\"QUIT\"" "\"221 \""',pty,echo=0,cr ////////////////////////////////////////////////////////////////////////////// // IP6 # socat readline TCP6:[::1]:21 # if your inetd/ftp is listening on ip6 /////////////////////////////////////////////////////////////////////////////// // application server solutions // run a program (here: /bin/sh) chrooted, unprivileged; // parent process stays in real / running as root # socat -d -d - EXEC:/bin/sh,chroot=/home/sandbox,su=sandbox,pty // make a program available on the network chrooted, unprivileged; // parent process stays in / running as root // script path is already chrooted # ./socat -lm -d -d TCP-LISTEN:5555,fork EXEC:/bin/myscript,chroot=/home/sandbox,su=sandbox,pty,stderr // to avoid terminal problems, you might - instead of telnet - connect using $ socat -,icanon=0,echo=0 tcp:target:5555; reset // access local display from ssh server, when ssh port forwarding is disabled // socat must be installed on ssh server host // might have to use xauth... // this example is one-shot because ssh can handle only one channel xterm1$ socat -d -d exec:"ssh www.dest-unreach.org rm -f /tmp/.X11-unix/X9; ~/bin/socat -d -d unix-l\:/tmp/.X11-unix/X9\,fork -" unix:/tmp/.X11-unix/X0 xterm2$ ssh target target$ DISPLAY=:9 myxapplication // touch with perms: // no race condition for perms (applied with creat() call) $ socat -u /dev/null creat:/tmp/tempfile,perm=0600 // touch with owner and perms: // race condition before changing owner, but who cares - only root may access # socat -u /dev/null creat:/tmp/tempfile,user=user1,perm=0600 // invoke an interactive ssh with exec // first example passes control chars (^C etc.) to remote server as usual socat -,echo=0,raw exec:'ssh server',pty,setsid,ctty // second example interprets control chars on local command line socat -,echo=0,icanon=0 exec:'ssh server',pty,setsid,ctty // afterwards, type "reset"! // convince ssh to provide an "interactive" shell to your script // three main versions for entering password: // 1) from your TTY; have 10 seconds to enter password: (sleep 10; echo "ls"; sleep 1) |socat - exec:'ssh server',pty // 2) from XWindows (DISPLAY !); again 10 seconds (sleep 10; echo "ls"; sleep 1) |socat - exec:'ssh server',pty,setsid // 3) from script (sleep 5; echo PASSWORD; echo ls; sleep 1) |./socat - exec:'ssh server',pty,setsid,ctty // download with proxy CONNECT // use echo -e if required for \n $ (echo -e "CONNECT HTTP/1.0\n"; sleep 5; echo -e "GET /download/file HTTP/1.0\n"; sleep 10) |socat -d -d -t 3600 - tcp:proxy:8080,crlf // retrieve a file from an sshd site with sourceforge style entry menu; // fill in your personal values; cat lets you enter your password (will be // visible on screen) $ (sleep 10; read pass; echo $pass; sleep 10; echo M; sleep 5; echo cat FILENAME; sleep 10) |./socat -d -d -ly - EXEC:'ssh -c 3des -l USER cf.sourceforge.net',pty,setsid,ctty |tee FILENAME // multicast community on local network: start the following command on all // participating hosts; like a conference call: # socat -d -d -d -d - udp-datagram:,bind=:6666,ip-add-membership=,bindtodevice=eth0 // or $ socat -d -d -d -d - udp-datagram:,bind=:6666,ip-add-membership= // possible reasons for failure: // iptables or other filters (open your filters as required) // packets leave via wrong interface (set route: ...) // socket bound to specific address //============================================================================= // GENERIC FUNCTION CALLS // ioctl(): open CD drive (given value valid on Linux) // on my Linux system I find in /usr/include/linux/cdrom.h the define: // #define CDROMEJECT 0x5309 /* Ejects the cdrom media */ // the following command makes something like ioctl(fd, CDROMEJECT, NULL) // (don't care about the read error): $ socat /dev/cdrom,o-nonblock,ioctl-void=0x5309 - // setsockopt(): SO_REUSEADDR // the following command performs - beyond lots of overhead - something like: // myint=1; setsockopt(fd, SOL_SOCKET, SO_REUSEADDR, &myint, sizeof(myint)) $ socat -u udp-recv:7777,setsockopt-int=1:2:1 - // setsockopt(): SO_BINDTODEVICE // ways to apply SO_BINDTODEVICE without using the special socat address option // so-bindtodevice: // with string argument: $ sudo ./socat tcp-l:7777,setsockopt-string=1:25:eth0 pipe // with binary argument: $ sudo ./socat tcp-l:7777,setsockopt-bin=1:25:x6574683000 pipe =============================================================================== // not tested, just ideas, or have problems // traverse firewall for making internal telnet server accessible for outside // telnet client, when only outbound traffic (syn-filter) is allowed: // on external client run "double server". this process waits for a // connection from localhost on port 10023, and, when it is established, waits // for a connection from anywhere to port 20023: ext$ socat -d TCP-LISTEN:10023,range=localhost TCP-LISTEN:20023 // on internal server run double client: int$ socat -d TCP:localhost:23 TCP:extclient:10023 // or, with socks firewall: int$ socat -d TCP:localhost:23 SOCKS:socksserver:extclient:10023 // login with: ext$ telnet localhost 20023 // you can make a double server capable of handling multiple instances: ext$ socat -d TCP-LISTEN:10023,range=localhost,fork TCP-LISTEN:20023,reuseaddr // access remote display via ssh, when ssh port forwarding is disabled $ socat -d -d EXEC:"ssh target socat - UNIX:/tmp/.X11-unix/X0" TCP-LISTEN:6030 $ xclock -display localhost:30 // relay multiple webserver addresses through your firewall into your DMZ: // make IP aliases on your firewall, and then: # socat -d -d TCP-L:80,bind=fw-addr1,fork TCP:dmz-www1:80 # socat -d -d TCP-L:80,bind=fw-addr2,fork TCP:dmz-www2:80 // and for improved security: # socat -d -d TCP-L:80,bind=fw-addr3,su=nobody,fork TCP:dmz-www3:80 // proxy an arbitrary IP protocol over your firewall (answers won't work) # socat -d -d IP:,bind=fwnonsec IP:sec-host:150,bind=fwsec // proxy an unsupported IP protocol over your firewall, point to point // end points see firewall interfaces as IP peers! # socat -d -d IP:nonsec-host:150,bind=fwnonsec IP:sec-host:150,bind=fwsec // note that, for IPsec, you might face problems that are known with NAT