This seems a brute force attack. You can use fail2ban to prevent it.

http://www.fail2ban.org/wiki/index.php/Main_Page

And strong passwords, of course.

-----Mensaje original-----
De: listbounce (at) securityfocus (dot) com [email concealed] [mailto:listbounce (at) securityfocus (dot) com [email concealed]]
En nombre de Richard Chapman
Enviado el: viernes, 02 de mayo de 2008 15:55
Para: secureshell (at) securityfocus (dot) com [email concealed]
Asunto: ssh security question

Hi
I don't now much about ssh - but I use it to connect to my centos server

with nx. Normally - I only do this on our local network and have port 22

disabled in the internet firewall.
Recently - I was away from the office - and enabled port 22 on the
firewall - so I could access the centos server remotely. I thought ssh
had pretty good security - and nx uses a key to allow access.

However - after only a day with port 22 enabled - I had some sort of
attack reported by the firewall - and I had the following in my
logwatch...

--------------------- pam_unix Begin ------------------------

smtp:
Unknown Entries:
authentication failure; logname= uid=0 euid=0 tty= ruser= rhost=
: 155 Time(s)
check pass; user unknown: 155 Time(s)
authentication failure; logname= uid=0 euid=0 tty= ruser= rhost=
user=richard: 1 Time(s)
bad username [!]: 1 Time(s)
bad username [*]: 1 Time(s)

sshd:
Authentication Failures:
unknown (60.12.1.158): 1581 Time(s)
root (60.12.1.158): 82 Time(s)
sshd (60.12.1.158): 4 Time(s)
mysql (60.12.1.158): 3 Time(s)
richard (60.12.1.158): 3 Time(s)
gopher (60.12.1.158): 2 Time(s)
halt (60.12.1.158): 2 Time(s)
mail (60.12.1.158): 2 Time(s)
mailnull (60.12.1.158): 2 Time(s)
max (60.12.1.158): 2 Time(s)
nfsnobody (60.12.1.158): 2 Time(s)
nobody (60.12.1.158): 2 Time(s)
postgres (60.12.1.158): 2 Time(s)
squid (60.12.1.158): 2 Time(s)
adm (60.12.1.158): 1 Time(s)
ais (60.12.1.158): 1 Time(s)
apache (60.12.1.158): 1 Time(s)
bin (60.12.1.158): 1 Time(s)
daemon (60.12.1.158): 1 Time(s)
ftp (60.12.1.158): 1 Time(s)
games (60.12.1.158): 1 Time(s)
gdm (60.12.1.158): 1 Time(s)
haldaemon (60.12.1.158): 1 Time(s)
lp (60.12.1.158): 1 Time(s)
named (60.12.1.158): 1 Time(s)
news (60.12.1.158): 1 Time(s)
nscd (60.12.1.158): 1 Time(s)
ntp (60.12.1.158): 1 Time(s)
nut (60.12.1.158): 1 Time(s)
operator (60.12.1.158): 1 Time(s)
pcap (60.12.1.158): 1 Time(s)
piranha (60.12.1.158): 1 Time(s)
postfix (60.12.1.158): 1 Time(s)
rpc (60.12.1.158): 1 Time(s)
rpcuser (60.12.1.158): 1 Time(s)
rpm (60.12.1.158): 1 Time(s)
shutdown (60.12.1.158): 1 Time(s)
smmsp (60.12.1.158): 1 Time(s)
sync (60.12.1.158): 1 Time(s)
tim (60.12.1.158): 1 Time(s)
uucp (60.12.1.158): 1 Time(s)
webalizer (60.12.1.158): 1 Time(s)
Invalid Users:
Unknown Account: 1581 Time(s)

Can anyone tell me what is going on here. It looks like someone is
trying to find usernames by just testing a list. They appear to have
found 3 of our usernames - but hopefully not the passwords.

How much of a security issue is this? If they did guess a password -
would they have full shell access? If so - how is this any better than
(say) telnet?

Are there any settings I can and should do to restrict access further? I

have blocked port 22 in the firewall for the time being. Can I set up a
shared private key or similar?

Many thanks

Richard

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