-----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-----
_______________________________________________
freebsd-security@freebsd.org mailing list
http://lists.freebsd.org/mailman/listinfo/freebsd-security
To unsubscribe, send any mail to "[EMAIL PROTECTED]"
