Posts Tagged ‘testuser’

Maximal protection against SSH attacks. If your server has to stay with open SSH (Secure Shell) port open to the world

Thursday, April 7th, 2011

Reading Time: 5minutes
Brute Force Attack SSH screen, Script kiddie attacking
If you’re a a remote Linux many other Unix based OSes, you have defitenily faced the security threat of many failed ssh logins or as it’s better known a brute force attack

During such attacks your /var/log/messages or /var/log/auth gets filled in with various failed password logs like for example:

Feb 3 20:25:50 linux sshd[32098]: Failed password for invalid user oracle from port 51490 ssh2
Feb 3 20:28:30 linux sshd[32135]: Failed password for invalid user oracle1 from port 42778 ssh2
Feb 3 20:28:55 linux sshd[32141]: Failed password for invalid user test1 from port 51072 ssh2
Feb 3 20:30:15 linux sshd[32163]: Failed password for invalid user test from port 47481 ssh2
Feb 3 20:33:20 linux sshd[32211]: Failed password for invalid user testuser from port 51731 ssh2
Feb 3 20:35:32 linux sshd[32249]: Failed password for invalid user user from port 38966 ssh2
Feb 3 20:35:59 linux sshd[32256]: Failed password for invalid user user1 from port 55850 ssh2
Feb 3 20:36:25 linux sshd[32268]: Failed password for invalid user user3 from port 36610 ssh2
Feb 3 20:36:52 linux sshd[32274]: Failed password for invalid user user4 from port 45514 ssh2
Feb 3 20:37:19 linux sshd[32279]: Failed password for invalid user user5 from port 54262 ssh2
Feb 3 20:37:45 linux sshd[32285]: Failed password for invalid user user2 from port 34755 ssh2
Feb 3 20:38:11 linux sshd[32292]: Failed password for invalid user info from port 43146 ssh2
Feb 3 20:40:50 linux sshd[32340]: Failed password for invalid user peter from port 46411 ssh2
Feb 3 20:43:02 linux sshd[32372]: Failed password for invalid user amanda from port 59414 ssh2
Feb 3 20:43:28 linux sshd[32378]: Failed password for invalid user postgres from port 39228 ssh2
Feb 3 20:43:55 linux sshd[32384]: Failed password for invalid user ftpuser from port 47118 ssh2
Feb 3 20:44:22 linux sshd[32391]: Failed password for invalid user fax from port 54939 ssh2
Feb 3 20:44:48 linux sshd[32397]: Failed password for invalid user cyrus from port 34567 ssh2
Feb 3 20:45:14 linux sshd[32405]: Failed password for invalid user toto from port 42350 ssh2
Feb 3 20:45:42 linux sshd[32410]: Failed password for invalid user sophie from port 50063 ssh2
Feb 3 20:46:08 linux sshd[32415]: Failed password for invalid user yves from port 59818 ssh2
Feb 3 20:46:34 linux sshd[32424]: Failed password for invalid user trac from port 39509 ssh2
Feb 3 20:47:00 linux sshd[32432]: Failed password for invalid user webmaster from port 47424 ssh2
Feb 3 20:47:27 linux sshd[32437]: Failed password for invalid user postfix from port 55615 ssh2
Feb 3 20:47:54 linux sshd[32442]: Failed password for www-data from port 35554 ssh2
Feb 3 20:48:19 linux sshd[32448]: Failed password for invalid user temp from port 43896 ssh2
Feb 3 20:48:46 linux sshd[32453]: Failed password for invalid user service from port 52092 ssh2
Feb 3 20:49:13 linux sshd[32458]: Failed password for invalid user tomcat from port 60261 ssh2
Feb 3 20:49:40 linux sshd[32464]: Failed password for invalid user upload from port 40236 ssh2
Feb 3 20:50:06 linux sshd[32469]: Failed password for invalid user debian from port 48295 ssh2
Feb 3 20:50:32 linux sshd[32479]: Failed password for invalid user apache from port 56437 ssh2
Feb 3 20:51:00 linux sshd[32492]: Failed password for invalid user rds from port 45540 ssh2
Feb 3 20:51:26 linux sshd[32501]: Failed password for invalid user exploit from port 53751 ssh2
Feb 3 20:51:51 linux sshd[32506]: Failed password for invalid user exploit from port 33543 ssh2
Feb 3 20:52:18 linux sshd[32512]: Failed password for invalid user postgres from port 41350 ssh2
Feb 3 21:02:04 linux sshd[32652]: Failed password for invalid user shell from port 54454 ssh2
Feb 3 21:02:30 linux sshd[32657]: Failed password for invalid user radio from port 35462 ssh2
Feb 3 21:02:57 linux sshd[32663]: Failed password for invalid user anonymous from port 44290 ssh2
Feb 3 21:03:23 linux sshd[32668]: Failed password for invalid user mark from port 53285 ssh2
Feb 3 21:03:50 linux sshd[32673]: Failed password for invalid user majordomo from port 34082 ssh2
Feb 3 21:04:43 linux sshd[32684]: Failed password for irc from port 50918 ssh2
Feb 3 21:05:36 linux sshd[32695]: Failed password for root from port 38577 ssh2
Feb 3 21:06:30 linux sshd[32705]: Failed password for bin from port 53564 ssh2
Feb 3 21:06:56 linux sshd[32714]: Failed password for invalid user dev from port 34568 ssh2
Feb 3 21:07:23 linux sshd[32720]: Failed password for root from port 43799 ssh2
Feb 3 21:09:10 linux sshd[32755]: Failed password for invalid user bob from port 50026 ssh2
Feb 3 21:09:36 linux sshd[32761]: Failed password for invalid user r00t from port 58129 ssh2
Feb 3 21:11:50 linux sshd[537]: Failed password for root from port 58358 ssh2

This brute force dictionary attacks often succeed where there is a user with a weak a password, or some old forgotten test user account.
Just recently on one of the servers I administrate I have catched a malicious attacker originating from Romania, who was able to break with my system test account with the weak password tset .

Thanksfully the script kiddie was unable to get root access to my system, so what he did is he just started another ssh brute force scanner to crawl the net and look for some other vulnerable hosts.

As you read in my recent example being immune against SSH brute force attacks is a very essential security step, the administrator needs to take on a newly installed server.

The easiest way to get read of the brute force attacks without using some external brute force filtering software like fail2ban can be done by:

1. By using an iptables filtering rule to filter every IP which has failed in logging in more than 5 times

To use this brute force prevention method you need to use the following iptables rules:
linux-host:~# /sbin/iptables -I INPUT -p tcp --dport 22 -i eth0 -m state -state NEW -m recent -set
linux-host:~# /sbin/iptables -I INPUT -p tcp --dport 22 -i eth0 -m state -state NEW
-m recent -update -seconds 60 -hitcount 5 -j DROP

This iptables rules will filter out the SSH port to an every IP address with more than 5 invalid attempts to login to port 22

2. Getting rid of brute force attacks through use of hosts.deny blacklists

sshbl – The SSH blacklist, updated every few minutes, contains IP addresses of hosts which tried to bruteforce into any of currently 19 hosts (all running OpenBSD, FreeBSD or some Linux) using the SSH protocol. The hosts are located in Germany, the United States, United Kingdom, France, England, Ukraine, China, Australia, Czech Republic and setup to report and log those attempts to a central database. Very similar to all the spam blacklists out there.

To use sshbl you will have to set up in your root crontab the following line:

*/60 * * * * /usr/bin/wget -qO /etc/hosts.deny

To set it up from console issue:

linux-host:~# echo '*/60 * * * * /usr/bin/wget -qO /etc/hosts.deny' | crontab -u root -

These crontab will download and substitute your system default hosts with the one regularly updated on , thus next time a brute force attacker which has been a reported attacker will be filtered out as your Linux or Unix system finds out the IP matches an ip in /etc/hosts.deny

The /etc/hosts.deny filtering rules are written in a way that only publicly known brute forcer IPs will only be filtered for the SSH service, therefore other system services like Apache or a radio, tv streaming server will be still accessible for the brute forcer IP.

It’s a good practice actually to use both of the methods 😉
Thanks to Static (Multics) a close friend of mine for inspiring this article.

Enabling talkd (Console Chat) between logged in users on FreeBSD and other BSDs

Sunday, June 10th, 2012

Reading Time: 2minutes

Talk between two useres on FreeBSD 7.2 screenshot, console peer to peer interactive talk program UNIX, Linux, BSD

Those who are in familiar with older UNIXes, UNIX BSD derivatives and GNU Linux should certainly remember the times, when we hackers used to talk to each other using talk service.

Those who don't know what talk command is it is a simple console / ssh utility to talk to another logged in users.

Talk is very similar to write and mesg one liner messasing utilities available for *nixes, the difference is it is intendted to provide interactive chat between the two logged in users. People who came to know UNIX or free software in older times most likely don't know talk, however I still remember how precious this tool was for communication back in the day.

I believe still it can be useful so I dediced to install ot on one FreeBSD host.

In order to have the talk service running on BSD it is necessery to have /usr/libexec/ntalkd installed on the system this however is installed by default with standard BSD OS installs, so no need for any external ports install to run it.

talk doesn't have it's own init script to start is not written to run as it own service but in order to run it is is necessery to enable it via inetd

Enabling it is done by;;;

1 — Editting /etc/inetd.conf

Inside the conf the line::

#ntalk dgram udp wait tty:tty /usr/libexec/ntalkd ntalkd

should be uncommented e.g, become ;;;

ntalk dgram udp wait tty:tty /usr/libexec/ntalkd ntalkd

2 — Restart inetd

freebsd# /etc/rc.d/inetd restart
Stopping inetd.
Starting inetd.

talk is planned to be used for peer to peer conversations over SSH so in a way it is the GRANDFATHER 🙂 of IRC, ICQ and Skype;;;

Here is an example on how talk is used ,, Let's say there are three logged in users

pcfreak# w
12:39PM up 3 days, 16:25, 3 users, load averages: 1.12, 0.91, 0.71
testuser p0 10:50AM - bash
hipo p3 12:23PM - w
root p4 :ttyp2:S.0 12:24PM - vim /usr/local/www/dat

I'm logged in with my username hipo and I would like to talk to testuser ;;;;

pcfreak% tty

You see I'm logged in on /dev/ttyp3 (this is the specific naming on BSDs) on Linux equivalent is /dev/tty3So to talk the other user testuser;;;;;-

$ talk testuser ttyp0
[No connection yet]
[Waiting for your party to respond]

The testuser logged in via SSH will then get a message ||;

Message from Talk_Daemon@pcfreak at 12:44 on 2012/06/10 ...
talk: connection requested by hipo@localhost
talk: respond with: talk hipo@localhost

To enter a talk session then the logged in testuser has to type:

$ talk hipo@localhost


Error from park wrapper: is already configured. Sorry, that domain is already setup (remove it from httpd.conf) – How to solve

Monday, July 4th, 2011

Reading Time: < 1minute
If you’re administrating a Cpanel server and you come across an error message while trying to use cpanel’s domain addon menu and you want to fix that you will need to do the following logged in as root over an ssh connection:

1. Remove dns related stuff in /var/named and /var/named/cache cpanel:~# rm -f /var/named/ rm -f /var/named/cache/

2. Edit the current used httpd.conf on the server and remove all virtualhost domain definitions

cpanel:~# vim /etc/httpd/conf/httpd.conf
# find the Virtualhost definitions and completely remove them

3. Remove any domain occurance in /var/cpanel/users

cpanel:~# cd /var/cpanel/users/
cpanel:/var/cpanel/users# grep -rli '' *
cpanel:~# vim /var/cpanel/users/hipo
# remove in above file any domain related entries

3. Remove anything related to in /etc/userdomains and /etc/localdomains

cpanel:~# vim /etc/userdomains
cpanel:~# vim /etc/localdomains
# again look inside the two files and remove the occuring entries

4. Edit /etc/named.conf and remove any definitions of

cpanel:~# vim /etc/named.conf
# in above file remove DNS configuration for

5. Run /scripts/updateuserdomains

cpanel:~# /scripts/updateuserdomains

6. Delete any valias configurations

cpanel:~# rm -f /etc/valiases/
cpanel:~# rm -f /etc/vdomainaliases/
cpanel:~# rm -f/etc/vfilters/

7. Remove any occurance of in the user directory which experiences the Error from park wrapper: error

Let’s say the user testuser is experiencing the error, in that case you will have to remove:

cpanel:~# rm -rf /home/testuser/public_html/

8. Restart Cpanel

This step is optional though I think it’s also a good practice as it will at least restart the Cpanel webserver (Apache or Litespeed depending on your conf)

cpanel:~# /etc/init.d/cpanel restart

Now try to add up the domain via the Cpanel domain addon interface, hopefully the issue should be fixed by now. If not you might also check if there is no some record about in the mysql server.
Cheers 😉

How to fix “delivery 1: deferral: Sorry,_message_has_wrong_owner._(#4.3.5)/” qmail mail delivery failure message

Friday, May 20th, 2011

Reading Time: 2minutes
After a failed attempt to enable some wrapper scripts to enable domain keys support in a qmail powered mail server my qmail server suddenly stopped being able to normally send mail.

The exact error message which was logged in /var/log/qmail/current was:

@400000004dd66fcc16a088ac delivery 1: deferral: Sorry,_message_has_wrong_owner._(#4.3.5)/

This qmail messed happened after I substituted /var/qmail/bin/qmail-queue and /var/qmail/bin/qmail-remote with two respective wrapper shell scripts which were calling for the original qmail-queue and qmail-remote binaries under the names qmail-queue.orig and qmail-queue.orig

Restoring back qmail-queue.orig to /var/qmail/bin/qmail-queue and qmail-remote.orig to /var/qmain/bin/qmail-remote and restarting the mail server broke my qmail install.

After a bunch of nerves trying to isolate what is causing the error I found out that by mistake I forgot to copy the qmail-queue and qmail-remote permissions and ownership.

Thus I had to check another qmail working installation’s permissions for both binaries and fix the permissions to be equivalent to the permissions:

debian:~# ls -al /var/qmail/bin/qmail-remote
-rwx–x–x 1 root qmail 50464 2011-05-20 12:56 /var/qmail/bin/qmail-remote*
debian:~# ls -al /var/qmail/bin/qmail-queue
-rws–x–x 1 qmailq qmail 20392 2011-05-20 12:56 /var/qmail/bin/qmail-queue*

The exact chmod and chmod commands I issued to solve the shitty issues were as follows:

First I fixed the qmail-queue and qmail-remote ownership:

debian:~# chown qmailq:qmail /var/qmail/bin/qmail-queue
debian:~# chown root:qmail /var/qmail/bin/qmail-remote

Second I set the proper file permissions:

# make the qmail-queue binary suid
debian:~# chmod u+s /var/qmail/bin/qmail-queue
debian:~# chmod 611 /var/qmail/bin/qmail-queue
debian:~# chmod 611 /var/qmail/bin/qmail-remote

Third and last I did a restart of the qmail server and tested it sends properly

debian:~# /usr/bin/qmailctl stop
Stopping qmail...
debian:~# /usr/bin/qmailctl start
Starting qmail

Finally to test that the qmail server qmail-queue was queing and sending with qmail-remote I used the system mail command like so:

debian:~# mail -s "test email"

Afterwards the mail was properly received on my mail account immediately.

In my /var/log/qmail/current log file all seemed fine:

@400000004dd6702a2eb2b064 starting delivery 1: msg 85281596 to remote
@400000004dd6702a2eb2b834 status: local 0/20 remote 1/20
@400000004dd6702b34cc809c delivery 1: success:
@400000004dd6702b34cc886c status: local 0/20 remote 0/20
@400000004dd6702b34cc8c54 end msg 85281596

The test mail was properly received on my mail account immediately.

It took me like half an hour to figure out what exactly is wrong with the permissions in situations like this I really wanted to change all my qmail installs with postfix and forget forever I ever used qmail …