This post was authored byNick Biasini,Matt Olney, &Craig Williams

 

Introduction

Talos has been monitoring a persistent threat for quite some time, a group we refer to as SSHPsychos or Group 93. This group is well known for creating significant amounts of scanning traffic across the Internet. Although our research efforts help inform and protect Cisco customers globally, sometimes it is our relationships that can multiply this impact. Today Cisco and Level 3 Communications took action to help ensure a significantly larger portion of the Internet is also protected.

Graphic Showing SSH Psychos SSH Traffic vs Rest of Internet (Green)

Behavior

The primary focus of SSHPsychos has been SSH brute force attacks.  Based on passive DNS data the first activity was seen in June 2014.  Since then two class C networks have been generating unequalled amounts of SSH login attempts to every host that is listening.  The graphic above demonstrates the volume of login attempts these networks are attempting.  The traffic from SSHPsychos dwarfs the combined SSH login attempt traffic from the rest of the Internet. It is important to note that these netblocks appear to only be used for malicious activity.

High Level Overview of Attack

The behavior consists of large amounts of SSH brute force login attempts from103.41.124.0/23, only attempting to guess the password for the root user, with over 300,000 unique passwords.  Once a successful login is achieved the brute forcing stops. The next step involves a login from a completely different IP ranges owned by shared hosting companies based out of the United States.  After login is achieved a wget request is sent outbound for a single file which has been identified as a DDoS rootkit.  The file has been observed being downloaded from hardcoded IP addresses as well as from specific domains which resolve to the same address (23.234.60.140).  This address is associated with a hosting company based out of the United States.

Domain Information for Server Hosting DDoS Kit

Once the rootkit is installed additional instructions are downloaded via an XOR encoded file from one of the C2 servers.  Level 3 decoded one of the configuration files a sample of which can be found below.  The config file is largely constructed of a list of IP addresses that are being denied and filenames, and files to be deleted.

Sample Decoded config file (Click Image for actual config file)

Time for Action

Using the information Talos has gathered over the last several months, we began collaborating with Level 3 to determine what steps can be taken to address this threat and protect users. Level 3 analyzed the behavior of the suspect networks and confirmed that no legitimate traffic is originating or destined for 103.41.124.0/23. At this point Talos and Level 3 started the process to take down this particular netblock.

A Shift Occurs

As part of the process, Level 3 worked to notify the appropriate providers regarding the change. On March 30th SSHPsychos suddenly pivoted. The original /23 network went from a huge volume of SSH brute force attempts to almost no activity and a new /23 network began large amounts of SSH brute forcing following the exact same behavior associated with SSHPsychos. The new network is43.255.190.0/23 and its traffic was more than 99% SSH immediately after starting communication. The host serving the malware also changed and a new host (23.234.19.202) was seen providing the same file as discussed before a DDoS Rootkit.

SSHPsychos SSH Traffic (103.41.124.0/23 -Red & Pink, 43.255.190.0/23 -Orange, All Other SSH Traffic -Green)

Based on this sudden shift, immediate action was taken. Talos and Level 3 decided to remove the routing capabilities for 103.41.124.0/23, but also add the new netblock 43.255.190.0/23. The removal of these two netblocks introduced another hurdle for SSHPsychos, and hopefully slows their activity, if only for a short period.

An operation of this size would only be possible with the collaboration of Level 3 and Cisco to make the Internet safer. In the future, we only see this type of operation being undertaken when we can prevent systems from being compromised without any impact to legitimate Internet activity.

IOC

Domains:
ftp.rxxiaoao.com
ndns.dsaj2a.org
ndns.dsaj2a1.org
ndns.hcxiaoao.com
ndns.dsaj2a.com
ns1.hostasa.org
ns2.hostasa.org
ns3.hostasa.org
ns4.hostasa.org
aa.hostasa.org
info.3000uc.org

IP Addresses:
Scanning:
103.41.124.0/23
43.255.190.0/23 

Command & Control:
103.240.140.152
103.240.141.54
103.240.141.50
104.143.5.25
162.218.112.7

Malware Hosting:
23.234.60.140
23.234.60.143
23.234.19.202

SSH Password List
Rootkit Config File Sample

Conclusion

Gone are the days when detectors and protectors can sit on the Internet's sidelines when a group is brazenly attacking a wide range of systems around the world. This specific threat was known to the security community, but Cisco and Level 3 Communications agreed that it was time to step in and make it stop. Together we severely limited SSHPsychos ability to communicate within Level 3 Communications backbone, and hindered their ability to compromise systems and proliferate their malware.

While these changes protect the portions of the Internet overseen by Level 3, we believe there is still more to be done. We ask that others join us to stop malicious traffic from spreading on the internet. We encourage ISPs and network administrators to join our efforts to curb this specific group, by removing the routes for these networks in a controlled and responsible manner. If we work together, we have the opportunity to eliminate a group that is making no effort to hide their malicious activity.

If you support the idea of taking action against this group and others that openly attack the Internet, add your voice by tweeting#DownWithSSHPsychos.