-----BEGIN PGP SIGNED MESSAGE----- Hash: SHA1 On Sat, 19 Aug 2006, Pieter de Boer wrote: > Gang, > > For months now, we're all seeing repeated bruteforce attempts on SSH. I've > configured my pf install to ratelimit TCP connections to port 22 and to > automatically add IP-addresses that connect too fast to a table that's > filtered: > > table <lamers> { } > > block quick from <lamers> to any > > pass in quick on $ext_if inet proto tcp from any to ($ext_if) port 22 > modulate state (source-track rule max-src-nodes 8 max-src-conn 8 > max-src-conn-rate 3/60 overload <lamers> flush global) > > > This works as expected, IP-addresses are added to the 'lamers'-table every > once in a while. > > However, there apparently are SSH bruteforcers that simply use one connection > to perform a brute-force attack: > > Aug 18 00:00:01 aberdeen sshd[87989]: Invalid user serwis from 83.19.113.122 > Aug 18 00:00:03 aberdeen sshd[88010]: Invalid user serwis from 83.19.113.122 > Aug 18 00:00:05 aberdeen sshd[88012]: Invalid user serwis from 83.19.113.122 > Aug 18 00:00:10 aberdeen sshd[88014]: Invalid user serwis from 83.19.113.122 > Aug 18 00:00:13 aberdeen sshd[88019]: Invalid user serwis from 83.19.113.122 > Aug 18 00:00:14 aberdeen sshd[88021]: Invalid user serwis from 83.19.113.122 > > > My theory was/is that this particular scanner simply multiplexes multiple > authentication attempts over a single connection. I 'used the source luke' of > OpenSSH to find support for this theory, but found the source a bit too > wealthy for my brain to find such support. > > So, my question is: Does anyone know how this particular attack works and if > there's a way to stop this? If my theory is sound and OpenSSH does not have > provisions to limit the authentication requests per TCP session, I'd find > that an inadequacy in OpenSSH, but I'm probably missing something here :) Isn't it the "MaxAuthTries" option for sshd which provides such functionality? Please look for "MaxAuthTries" in the sshd_config(5) manpage for details. regards Joerg - -- The beginning is the most important part of the work. -Plato -----BEGIN PGP SIGNATURE----- Version: GnuPG v1.4.5 (FreeBSD) iD8DBQFE54MNSPOsGF+KA+MRAh0GAJ45v4C9+xJ5vy+4BPltXwBxpKzzIwCePWa8 o/XSdoB2tFdMXQv1Yo1rwFU= =dHjL -----END PGP SIGNATURE----- _______________________________________________ [email protected] mailing list http://lists.freebsd.org/mailman/listinfo/freebsd-security To unsubscribe, send any mail to "[email protected]"