Dirk Hart

Inexpensive and informative Apple related e-books:

Take Control of Numbers

Take Control of Security for Mac Users

Take Control of OS X Server

Take Control of Preview

El Capitan: A Take Control Crash Course

Wed Mar 2 13:23:29 2005: 99   anonymous


Yap, pretty sure I'm going to ban all of Korea and China from ssh on my server.

--dhh



Wed Mar 2 23:18:16 2005: 103   TonyLawrence


There's a pam module for blacklisting: (link)

Might be useful..







Fri Mar 4 00:20:06 2005: 105   adanac


This is what you might see in your log if VerifyReverseMapping fails:

Mar 3 17:46:34 mammoth sshd[26428]: Illegal user jordan from 205.246.18.240
Mar 3 17:46:34 mammoth sshd[26428]: Address 205.246.18.240 maps to monolith.vet
eransadvantage.com, but this does not map back to the address - POSSIBLE BREAKIN
ATTEMPT!






Wed Nov 2 00:25:44 2005: 1267   anonymous


Actually what I've done to date is I put together a list of IP blocks I deny SSH access to by default on every system I build. The list started with all Non-Arin IP blocks and was peared down as I found places where I was a little too aggressive. I also wrote a perl script which I cron to run every couple of minutes which parses my /var/log/secure file for SSH login failures. It then adds new deny entries to the /etc/hosts.allow file to block those IP address's if the number of failures exceeds a preset number in a preset time interval. IE: by default, if there are more than 10 login failures from the same IP address and the failures are less than 5 seconds apart on average, then it is added to host.allow automatically because it is considered a brute force attack. If there are more than 50 failures in total, regardless of the interval, the ip address is added. The script also adds a header block to the hosts.allow file where you can add in a "Whitelist" of IP addresses which will always be first in the list and therefore can never be denied.

Since I added these measures, the number of failed login attempts on any given day on my servers has dropped from over 7000 to less than a few hundred on a bad day.

If anyone is interested, there is a project on sourceforge which is similar to what I have written but is far mor feature rich. It is however written in python and I have no intention of ever installing python on any of my servers unless I absolutely have to. If anyone is interested in a copy of the script, feel free to e-mail me at cgardiner@quadrix.com.






Wed Jan 18 19:52:12 2006: 1521   apex

grep 'Failed password' /var/log/messages | cut -f 13 -d ' ' | grep '\.' | uniq -c

Sun Mar 26 02:26:10 2006: 1820   b0x


noob Debian user here

My 2 cents

/etc/cron.hourly/sshd_deny

grep 'Invalid user' /var/log/auth.log* | cut -d ']' --fields=2 | cut -d ' ' --fields=6 | uniq -dc | sort -nr | awk '{ print "sshd: " $2 "/255.255.255.255" }' > /etc/hosts.deny



Fri Sep 5 09:44:19 2008: 4525   Matey


Hello All:
Thanks for the info. (I am looking for Correct Syntax)!

We've been getting many of these would-be hackers on our site lately and I was trying to put all their IP addresses from /var/log/auth.log file into /etc/hosts.deny BUT I keep
getting errors from the system such as this one:

warning: /etc/hosts.deny, line 31: missing ":" separator

and so on...(many such lines)?
Here's a portion of my .deny file;

# ALL: PARANOID
ALL:
79.187.241.62:
82.50.250.22:
82.179.130.135:
69.80.255.165:
219.150.196.6:
83.16.112.18:
222.191.240.194:
219.150.196.0/12:
168.234.227.2:
219.150.196.6:
200.228.120.130:

Any ways as you can see I did put Colons : as separators. why then errors/warnings??

Any idea how you would input separators (using ) debian linux (ubuntu 704?)
BTW I used , (commas) before and got errors about them too?

Thank You!

BTW thanks to those who wrote the Automatic hosts.deny file population! I have not perfected that for my system yet but I get an idea (New to Linux at these levels)!
Regards;






Fri Sep 5 11:22:00 2008: 4526   TonyLawrence


Isn't the format

ALL:ipaddress
ALL:ipaddress

etc.??



Thu Mar 5 06:35:28 2009: 5605   PrestonKutzner


I'm sure you probably have already stumbled upon this utility already, but you could use denyhosts ( (link) ) to do what you're talking about. It is very configurable and watches your auth log as well as managing hosts.deny for you.



Thu Mar 5 11:37:46 2009: 5606   TonyLawrence


Well, I hadn't seen that before so I'm glad you took the time to point us at it!



Thu Mar 5 23:48:43 2009: 5615   ToKy


Besides not allowing root logins I find that using public-keys is the best way to eliminate most of the things mentioned on this post.

Now, when you create your keys you better put a passphrase to it. Even though its pretty difficult for someone to get your private key, if they do and you didn't put a passphrase on your key....they just got VIP access to your server. Once the pubkey is setup then disable passwordauthentication and thats that, no more brute force thru ssh!

On your sshd_config file:
PubkeyAuthentication yes

TRY to set it up locally first before you try to do it remotly other wise you might lock yourself out!







Fri Mar 6 03:20:29 2009: 5616   TonyLawrence


Yes, of course. See (link) here for instructions.



Fri Mar 6 04:13:15 2009: 5617   PrestonKutzner


Well, glad I could help with denyhosts. I've been using it on several servers I administer. It's also handy in that it can be configured to email you when it blocks an IP address. It can add a bit of noise to the SNR, but can be handy to keep an eye on what's going on with regards to SSH on your systems. You can be fairly granular with the configuration too, which I personally like. In general, it's been a good tool in my experience.

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