FortiGuard Labs Breaking Threat Research
FortiGuard Labs has been monitoring a Linux coin mining campaign from “Rocke” – a malware threat group specializing in cryptomining. Over the past month we have seen new features constantly being added to the malware. For instance, in their latest major update, they have added a function that exploits systems running the software development automation server Jenkins to increase their chance of infecting more systems, thereby generating more profits. In addition, they have also evolved their malware by adding new attack stages, as well as new redundancies in its multi-component execution to make it more dynamic and flexible.
This post will go through the general behaviour of the malware as well as the new features we have documented having been added during our monitoring.
Figure 1: Basic Execution Flow
Stage1 and Stage2
The malicious bash script components of the malware are hosted in Pastebin, with the profile name “SYSTEMTEN”, which is very similar to previous names used by the “Rocke” threat group. It’s worth noting that most of the time there can be several paste links that point to the same script. Presumably, the redundancy is for operational continuity in case, for some reason, other links are removed. The paste links for the scripts seem to change every few days so that manually monitoring the threat can be tedious. Similar redundancies can also be found in other parts of this malware’s behavior.
Figure 2: Pastebin Profile Hosting the Scripts
In a nutshell, the infection begins after the execution of the Stage1 script, which may be installed to a system through various means, including manual intrusions, lateral movement from previous infections inside the network, from classic automated internet vulnerability scanning, service login brute-forcing, and exploitations.
The sole purpose of the Stage1 script is simply to download the Stage2 script via either wget or curl command and then execute it.
Figure 3: Stage1 Script
The Stage2 portion of the attack then performs the following:
- Adds a CRON job that downloads and executes the Stage1 script periodically. In this case, * * * * * means the script will execute every minute.
Figure 4: Adding CRON Job for Stage1
- Maximizes usage of the system’s processing power by terminating processes related to other miners.
Figure 5: Terminating Existing Miners
- Downloads the main payload binary appropriate to the system’s architecture (x32/x64). Two different download URLs are assigned to each architecture just in case either of them is inaccessible. It is also interesting to note that there is often a link that contains a timestamp suggesting its upload or compile time.
Figure 6: Downloading Main Payload
In older variants, the download links would all lead straight to the binary payload—until just a few days ago, when they decided to add a new loader stage before the actual execution of the payload. In the case of this recent version, some of the links are now serving large python scripts embedded with the base64-encoded ELF binary, which then decompresses and executes the main binary payload.
Figure 7: New Loader Binary for the Main Payload
- The malware is spread laterally by executing the Stage1 script and accessing the SSH known_hosts file, which contains SSH hosts that the victim’s system had previously connected to. A second test is performed to verify that public key authentication is possible.
Figure 8: Propagating Through SSH known_hosts
The main binary acts as a manager to the malware’s operation in the system. It ensures that the components are regularly updated, persistent, and hidden from the user. And ultimately, it executes the cryptominer.
The main payload is coded in Go Language (GoLang), and at first had been packed with a simple UPX. However, in March of this year, they switched to a “custom” UPX compression simply by changing the packed binaries’ section names to “LSD!”. It is a simple trick, but it can be very effective in evading file-based detection due to the fact that in most cases, engines can only decompress UPX-compressed files with proper headers.
Figure 9: Malware Switches to Custom UPX
Persistence and Stealth Mechanisms
This malware employs multiple persistence and stealth mechanisms to ensure its mining operation in an infected system.
It adds the service netdns to ensure that the payload binary, /usr/sbin/kerberods, executes on boot up.
Figure 10: Init Scripts for the Malware Service
Several CRON jobs have also been added that regularly download and execute the Stage1 script. This keeps the components updated to new developments from the threat developers. In older versions, these Pastebin URLs were all straightforward and hardcoded in the binary. In more recent variants, however, the Pastebin IDs have become more dynamic. Another stage was also added in the form of a new Pastebin URL where the IDs can be obtained. In case this URL is inaccessible, however, a hardcoded ID is still available for the malware to use.
Figure 11: Added CRON Jobs Pointing to the Stage1 Script
To hide its mining operation, a hooking library (usr/local/lib/<filename>.so) is installed for dynamic library preloading. It does this by adding the library’s path to ld.preload.so. In effect, the library is loaded to all new processes.
The library’s filename is obtained by randomly choosing from a list of hardcoded strings in the binary, contrary to the older variants that simply used one hardcoded filename. The image below shows just a few of the filenames that it can use.
Figure 12: Snippet of filename List
In a nutshell, the malware’s library component hooks functions so that any application trying to access information related to the malware will be presented with a fake result. These functions are related to the listing of files, network activities, processes, and CPU usage information.
Figure 13: Library with Hooked Functions Highlighted
For instance, if an application is trying to list a directory where a component of the malware resides, the library ensures that the malicious file will not be included in the result. To achieve this, the malware hooks the fopen API. The same principle applies to the other artifacts related to it, adding difficulty for victims to discover and remove the malware.
Figure 14: Hook Function For fopen
Figure 15: Hidden Library Function
In the case of concealing actual CPU statistics, if an application attempts to read the /proc/stat file, the function force_proc_cpu is called to return a hardcoded statistic showing a 0% CPU usage.
Figure 16: Function that Returns the Fake proc/stat
Figure 17: top Tool Display Before and After the Malicious Library is Preloaded
In earlier versions deployed in this campaign, this malware spread through a classic credential brute-force method targeting SSH (port 22) and Redis (port 6379) services. Basically, it scanned every IP address in the network and attempted to establish a session to these services using a long hardcoded list of credentials.
Figure 18: Propagate via CVE-2019-1003000
Figure 19: Propagate via CVE-2018-1000861
This campaign uses the open-source XMRig CPU miner. In older versions, a separate configuration file was dropped to the system with all the information included, including the wallet address of the threat actors and the mining pool that they use.
Figure 20: Miner Config from Older Versions
In these latest versions, the configuration is now embedded in the binary. The malware now uses a proxy server systemten.org:51640, (most probably running an xmrig-proxy service) for the mining traffic, where the wallet address and mining pool are configured. This means the infected host miners are not required to have the parameters, thereby effectively hiding the details for further investigation. Note that the port may change depending on the variant.
Figure 21: Embedded Miner Configuration with the Mining Pool Proxy
Through constant monitoring, we have observed that this is a very active campaign, often pushing multiple updates in a single day to add more features to their cryptomining scheme.
By utilizing a hook library, it is more complicated for users to manually detect and remove the infection from their systems, giving the threat actors more time to generate profit. We have also observed that they have started to add features to expand their infection by targeting system vulnerabilities, and given the recent rate of development, it’s likely that they will be adding more of these in the near future.
As always, FortiGuard Labs will be on the lookout for this campaign.
-= FortiGuard Lion Team =-
Fortinet customers are protected by the following solutions:
- The Jenkins exploits are detected by our IPS signature Jenkins.Script.Plugin.Authenticated.Remote.Command.Execution
- The traffic to the xmrig-proxy can be blocked using the application control signature Bitcoin.Cryptocurrency.Miner
- All malicious samples are detected as Linux/Agent.BQ!tr
- The miner’s proxy server is blocked by FortiGuard Web Filtering Service.
Read about the FortiGuard Security Rating Service, which provides security audits and best practices.
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