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dh2k 05-03-2013 04:17 AM

brute force attack detected in /var/log/messages
Hi Forum,

A brute force attack on sshd has been detected in /var/log/messages
cat /var/log/messages | grep sshd
cat /var/log/messages | grep Failed

I have the IP the attack has come from -
1/ any info on how to blacklist known IPs for sshd (and other/all services)

2/ I would really like to hear peoples imaginative suggestions for the known IPs ;-)


dc_eros 05-03-2013 04:36 AM


Take a look at here:


/sbin/iptables -I INPUT -s {IP-HERE} -j DROP
/sbin/iptables -I INPUT -s -j DROP

In my server though, only port 80 and port 443 are open to public. The rest are restricted to my home and office IP address like sshd.

TobiSGD 05-03-2013 04:49 AM

Install and configure fail2ban, exactly the service that you need for your purpose.

willysr 05-03-2013 06:05 AM

Or try sshblock which is available on SBo

rkelsen 05-03-2013 06:23 AM

How about configuring SSH to use shared keys? That way you can disable password logins altogether.

pan64 05-03-2013 07:27 AM


Originally Posted by rkelsen (Post 4944038)
How about configuring SSH to use shared keys? That way you can disable password logins altogether.

you can try to duckduckgo (google) on it, you can surely find a solution quickly.

just a comment:
instead of cat filename | grep pattern just use grep pattern filename

tronayne 05-03-2013 08:10 AM

There is also DenyHosts ( Been around for quite a while. It monitors your logs and when it sees this sort of activity it creates an entry for you in iptables or /etc/hosts.deny (either of these will stop a site from connecting); it's a daemon, it works (been using it for years).

Other options are country blocks, see for example You can get iptables or htaccess entries and just block the entire country (Chine, for example, is a good one to bock along with Russia, both Koreas, and others). You get list and write a little AWK program that creates the iptables entry, pretty easy.

If you're open to the Internet you're going to get whacked by script kiddies and bad actors (such as China); DenyHosts (along with the other methods in other posts above) is a good tool that you don't have fiddle with constantly and does a good job.

Hope this helps some.

kite 05-04-2013 12:47 AM

Why just block IP from China? Do you mean there is no bad hacker from US etc?

For sshd protection, normally I just change the port number.

dh2k 05-04-2013 01:41 AM

accesslists are to implemented (whitelists and blacklists) -
I will post more info on how to set these up for other viewers/readers.

Why does slackware have more than one 'messages' file? e.g.
ls -lah /var/log/ | grep messages
-rw-r--r-- 1 root root 460K May 4 07:26 messages
-rw-r--r-- 1 root root 1.8M Apr 26 04:30 messages.1
-rw-r--r-- 1 root root 170K Apr 7 04:34 messages.2
-rw-r--r-- 1 root root 358K Apr 4 04:26 messages.3
-rw-r--r-- 1 root root 190K Mar 24 04:38 messages.4


ponce 05-04-2013 02:30 AM

those are just rotated logs ("man logrotate").

BrZ 05-04-2013 02:30 AM

Rotation logs (logrotate). If you don't already, change the default port ASAP!

unSpawn 05-04-2013 03:05 AM


Originally Posted by dh2k (Post 4943950)
any info on how to blacklist known IPs for sshd (and other/all services)

Default answer, the SSH sticky:

Reasons for not using DenyHosts in its default configuration:
Reasons for not changing the port SSH listens on: /etc/services (as in IANA assigned ports aka interoperability and obfuscation)
Wrt using RBL's like DShield, I think its use is debatable as it doesn't relate to local conditions. In other words you may be investing resources in banning hosts that may have either scanned your particular ranges ages ago or will never scan your range RSN. (Also see this (2008) and this (more recent).)

tronayne 05-04-2013 07:26 AM


Originally Posted by kite (Post 4944581)
Why just block IP from China? Do you mean there is no bad hacker from US etc?

Of course there is "bad hacker" activity in/from the US (and pretty much every other country in the world); however, the lion's share originates in China.

Top 10 Source IPs

IP Address Reports Target IPs First Seen Last Seen () 358,888 111,812 2013-02-28 2013-05-04 (CN) 194,838 98,392 2013-04-01 2013-05-04 (CN) 264,319 92,567 2013-03-06 2013-05-04 (CN) 152,481 89,301 2013-03-18 2013-05-03 (IS) 436,078 83,118 2013-03-05 2013-05-04 (BY) 92,085 83,118 2013-03-28 2013-05-03 (IS) 564,139 78,938 2013-01-26 2013-05-04 (CN) 156,341 70,269 2013-03-16 2013-05-04 (GB) 70,226 68,918 2012-05-15 2013-05-04 (CN) 373,227 68,343 2013-03-17 2013-05-04
Who is (the one with no country code)?

% [ node-1]
% Whois data copyright terms

inetnum: -
netname:        CHINANET-SH
descr:          China Telecom
descr:          No.31,jingrong street
descr:          Beijing 100032
admin-c:        WWQ4-AP
tech-c:        WWQ4-AP
country:        CN
remarks:        service provider
remarks:        -+-+-+-+-+-+-+-+-+-+-+-++-+-+-+-+-+-+-+-+-+-+-+-+-+-+
remarks:        This object can only be updated by APNIC hostmasters.
remarks:        To update this object, please contact APNIC
remarks:        hostmasters and include your organisation's account
remarks:        name in the subject line.
remarks:        -+-+-+-+-+-+-+-+-+-+-+-++-+-+-+-+-+-+-+-+-+-+-+-+-+-+
changed: 20090821
mnt-by:        APNIC-HM
mnt-lower:      MAINT-CHINANET-SH
source:        APNIC

person:        Weng Wen Qian
address:        Room 2405,357 Songlin Road,Shanghai 200122
country:        CN
phone:          +86-21-68405784
fax-no:        +86-21-50623458
nic-hdl:        WWQ4-AP
mnt-by:        MAINT-CHINANET-SH
changed: 20050403
source:        APNIC

The source for the above is SANS Internet Storm Center ( Go look for yourself, all sorts of interesting data and reports.

While you're about it, go read and make up your own mind.

Script kiddies and port scanners are one thing, state-sponsored attacks are quite another. Do countries spy on one another? Of course they do and have done so for thousands of years in one form or another. It seem, though, that China has taken it to a new level.

Hope this helps some.

chemfire 05-04-2013 08:13 AM

Personally I don't see the need for fail2ban in this situation. Its one more package he has to install and one more thing that has to be memory resident. The kernel and some iptables rules already offer what is needed.

If you use a strong password or disable password authentication and use ssh keys than slowing down an attacker is enough to prevent a brute force attack from working and spare your logs.


iptables -A INPUT -p TCP -m state --state NEW -m recent --name probe_list --update --seconds 300 --hitcount 5 -j DROP

iptables -A INPUT -p TCP -s 0/0 --destination-port 22 -m state --state NEW -m recent --name probe_list --set

iptables -A INPUT -p TCP -s 0/0 --destination-port 22 -j ACCEPT

What this will do is cause netfilter to keep track of recent connection setups on port 22. It will have a hold time of 300 seconds, if there are more than 5 entries from the same source ip in that time it will refuse new connections. You can play with the hold time and hitcounts but I have found these values are very effective at stopping brute force attacks (they just give up and move on when they start seeing the port as closed after 5 hits) and not causing me any usability problems.

I would reserve things like fail2ban for other services like web applications where its normal for a client to be repeatedly establishing TCP sessions or anything UDP.

metageek 05-04-2013 08:39 AM

Disable password logins and allow only ssh keys. In addition disable remote root logins. Oh, and make your root password long.

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