SCTP is interesting ... multihoming means you can have several ips involved on each side of a connection (association in sctp speak) ... so when you move from wired to wireless your ssh session still is fine. If you find a proper SCTP ssh, of course.
Testing it on Ubuntu LTS, though, using socat for glue... a listening SCTP socket is invisible in netstat -ln. Fun. tcp, udp, raw sockets are visible ... but sctp isn't.
socat SCTP-LISTEN:8080,fork TCP-CONNECT:localhost:22
Nice, stealthy backdoor. Does not show in netstat(8) or ss(8). Combine with socat TCP-LISTEN:2223 SCTP-CONNECT:localhost:8080 on a remote host and we have a completely stealthy tunnel, if the firewall is mildly clue-challenged.
knan@ip:~$ netstat -ln Active Internet connections (only servers) Proto Recv-Q Send-Q Local Address Foreign Address State tcp 0 0 0.0.0.0:4949 0.0.0.0:* LISTEN tcp 0 0 0.0.0.0:22 0.0.0.0:* LISTEN tcp 0 0 127.0.0.1:631 0.0.0.0:* LISTEN tcp 0 0 127.0.0.1:25 0.0.0.0:* LISTEN udp 0 0 0.0.0.0:68 0.0.0.0:* udp 0 0 0.0.0.0:36558 0.0.0.0:* udp 0 0 0.0.0.0:5353 0.0.0.0:* udp 0 0 0.0.0.0:631 0.0.0.0:* udp 0 0 0.0.0.0:45561 0.0.0.0:* knan@ip:~$
lsof reports a mysterious socket. But it also does that for udev and update-manager, so that's hardly conclusive.
knan@ip:~$ lsof | grep socat | grep sock
socat 24969 knan 3u sock 0,6 0t0 645716 can't identify protocol
The only place I've dug out useful info so far is from procfs.
knan@ip:~$ cat /proc/net/sctp/eps ENDPT SOCK STY SST HBKT LPORT UID INODE LADDRS ffff8800722cb800 ffff8800342c8480 2 10 16 8080 1001 645716 0.0.0.0
Hardly easy to read. But it says LADDRS 0.0.0.0, LPORT 8080. Ok.
(BTW: SCTP not being in netstat is a Debian/Ubuntu-specific bug, SuSE/Red Hat have applied patches.)
sctp_darn(1) can do more fun sctp-specific stuff, like setting up multiple local and remote addresses for the association.
Cool enough. But there are other fun transport protocols we can try.
How about DCCP? It's connection-oriented and has congestion control but otherwise is UDP-like.
netsend dccp receive
knan@ip:~$ netstat -ln Active Internet connections (only servers) Proto Recv-Q Send-Q Local Address Foreign Address State tcp 0 0 0.0.0.0:4949 0.0.0.0:* LISTEN tcp 0 0 0.0.0.0:22 0.0.0.0:* LISTEN tcp 0 0 127.0.0.1:631 0.0.0.0:* LISTEN tcp 0 0 127.0.0.1:25 0.0.0.0:* LISTEN tcp6 0 0 :::22 :::* LISTEN tcp6 0 0 ::1:631 :::* LISTEN udp 0 0 0.0.0.0:68 0.0.0.0:* udp 0 0 0.0.0.0:36558 0.0.0.0:* udp 0 0 0.0.0.0:5353 0.0.0.0:* udp 0 0 0.0.0.0:631 0.0.0.0:* udp 0 0 0.0.0.0:45561 0.0.0.0:*Netstat still says nothing.
The only place in /proc/net you find DCCP mentioned is in /proc/net/protocols. Which says nothing about ongoing connections or listening sockets.
knan@ip:~$ grep -ir DCCP /proc/net/
/proc/net/protocols:DCCP 1400 1 -1 NI 1196 yes dccp_ipv4 y y y y y y y y y y y y n n y y y y n
lsof still says little.
knan@ip:~$ lsof | grep netsend | grep sock
netsend 25376 knan 3u sock 0,6 0t0 658124 can't identify protocol
ss(8) to the rescue! But only when you specifically ask it about DCCP sockets with -d.
knan@ip:~$ ss -ldn Recv-Q Send-Q Local Address:Port Peer Address:Port 0 0 *:6666 *:*
The final protocol I want to propose today is UDP-Lite. This is basically a UDP variant with partial checksums, for the case when garbled data is better than no data.
$ netsend udplite receive
As usual, netstat tells us nothing of this uncommon activity.
knan@ip:~$ netstat -ln Active Internet connections (only servers) Proto Recv-Q Send-Q Local Address Foreign Address State tcp 0 0 0.0.0.0:4949 0.0.0.0:* LISTEN tcp 0 0 0.0.0.0:22 0.0.0.0:* LISTEN tcp 0 0 127.0.0.1:631 0.0.0.0:* LISTEN tcp 0 0 127.0.0.1:25 0.0.0.0:* LISTEN tcp6 0 0 :::22 :::* LISTEN tcp6 0 0 ::1:631 :::* LISTEN udp 0 0 0.0.0.0:68 0.0.0.0:* udp 0 0 0.0.0.0:36558 0.0.0.0:* udp 0 0 0.0.0.0:5353 0.0.0.0:* udp 0 0 0.0.0.0:631 0.0.0.0:* udp 0 0 0.0.0.0:45561 0.0.0.0:*
This time, though, lsof identifies it!
knan@ip:~$ lsof | grep netsend
netsend 25461 knan 3u IPv4 661633 0t0 UDPLITE *:6666
Which is good, since ss doesn't.
To summarize (for Ubuntu 10.04 LTS):
| Protocol | netstat(8) | ss(8) | lsof(8) | /proc/net/* |
|---|---|---|---|---|
| SCTP | No | No | No | /proc/net/sctp/eps /proc/net/sctp6/eps |
| DCCP | No | Yes (-d) | No | No |
| UDP-Lite | No | No | Yes | /proc/net/udplite /proc/net/udplite6 |
Hope this leaves you entertained by the possibilities. Black hats begone!
P.S.
launchpad:netstat+sctp
launchpad:lsof+sctp
launchpad:lsof+dccp
