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We provide sophisticated cybersecurity solutions for Managed Security Service Providers (MSSPs), Managed Service Providers (MSPs), and Value-Added Resellers (VARs). Find out why you should partner with eSentire, the Authority in Managed Detection and Response, today.
Adversaries don’t work 9-5 and neither do we. At eSentire, our 24/7 SOCs are staffed with Elite Threat Hunters and Cyber Analysts who hunt, investigate, contain and respond to threats within minutes.
We have discovered some of the most dangerous threats and nation state attacks in our space – including the Kaseya MSP breach and the more_eggs malware.
Our Security Operations Centers are supported with Threat Intelligence, Tactical Threat Response and Advanced Threat Analytics driven by our Threat Response Unit – the TRU team.
In TRU Positives, eSentire’s Threat Response Unit (TRU) provides a summary of a recent threat investigation. We outline how we responded to the confirmed threat and what recommendations we have going forward.
Here’s the latest from our TRU Team…
What did we find?
Sorillus Remote Access Tool was identified within a healthcare customer’s environment in August 2022.
Sorillus is a Java-based cross-platform Remote Access Tool (RAT) compatible with Windows, Linux and macOS.
Like other RATs, Sorillus has the ability to collect system information, execute commands, browse files, and remotely control target machines among other features.
Figure 1 Image of Sorillus website
The RAT is sold via the Sorillus website for around €20 for lifetime access and according to the YouTube channel of the tool’s creator, a German-speaker known as Tapt, the tool was last updated in July 2022.
For the price, it’s generally received positively, although some question the long-term support considering the availability of supposed cracked versions.
Interest for Sorillus on hacking forums has increased in 2022 (Figure 2).
It was first mentioned on the “Deutschland im Deep Web” darknet forum in May 2020 and saw its most mentions in 2022 on forums such as HackForums and Cracked[.]io.
Figure 2 Unique mentions of Sorillus RAT
In the aforementioned case, the victim received a zip archive file containing “IMG-2022.jar” (fc748b0a2dca368f37a69740f0022fd468a4ef3634b286f86c9f65dc496af66a) via email.
The .JAR (Java Archive) packages contain code which executes when clicked by the victim. Decompiling the .JAR file reveals obfuscated/encrypted code, possibly using the Allatori Java Obfuscator.
Unlike previously observed samples, the string “sorillus” was not visible in the decompiled code.
Figure 3 Snippet of decompiled .JAR file showing code obfuscation.
Tracing the executed arguments reveals diagnostic strings in line with Sorillus RAT. In additional, captured C2 traffic matches known patterns for this RAT (Figure 5).
Figure 4 Decrypted strings with diagnostic information. Translation: "INSTANCE WAS NOT REMOVED (POSSIBLE FORGOTTEN?) (INSTANCE ID:)"
The RAT’s behavior is straightforward:
It copies itself to the user’s roaming profile.
Then, it uses Reg.exe to create an autostart registry key in HKEY_CURRENT_USER\Software\Microsoft\Windows\CurrentVersion\Run
Next, it uses icacls.exe to modify file permissions.
Lastly, it contacts severdops[.]ddns[.]net (208.67.106.143) over TCP port 1122, sends system information then awaits instructions via regular beacons/check-ins.
Figure 5 Packet capture of Sorillus C2 traffic. System information is sent followed by reoccurring check-ins.
How did we find it?
MDR for Endpoint identified suspicious behaviors and blocked network traffic to the C2 address.
What did we do?
Our team of 24/7 Cyber SOC Analysts alerted and isolated the hosts in accordance with the customer policy.
We also provided ongoing threat investigation updates to the customer.
What can you learn from this TRU positive?
Remote Access Tools (RATs) are a common part of threat actor toolkits and provide a flexible means to remotely control and exploit systems for fraud or furthering of intrusion objectives.
These tools can be deployed alongside other malware such as cryptominers or infostealers to maximize monetization opportunities.
Sorillus is a moderately capable RAT but is unlikely to see success long-term due to availability of cracked versions and one-time purchase model.
In contrast, the malware-as-a-service model used by the top infostealers such as as Redline or Raccoon Stealer generates generates reoccurring income. Plus, competition between the stealers motivates cybercrime operators to continuously tune their malware to evade defenses.
Recommendations from our Threat Response Unit (TRU) Team:
Rotate passwords and check for unusual connections / logons through the corporate VPN or Remote Desktop. Use of Multi-Factor Authentication (MFA) services can reduce impact of stolen credentials.
Ask Yourself...
What controls are in place to prevent or detect user execution of Java files?
Are you monitoring your endpoints 24/7 and what degree of control do you have to initiate a kill switch when required?
eSentire’s Threat Response Unit (TRU) is a world-class team of threat researchers who develop new detections enriched by original threat intelligence and leverage new machine learning models that correlate multi-signal data and automate rapid response to advanced threats.
If you are not currently engaged with an MDR provider, eSentire MDR can help you reclaim the advantage and put your business ahead of disruption.
Learn what it means to have an elite team of Threat Hunters and Researchers that works for you. Connect with an eSentire Cybersecurity Specialist.
eSentire Threat Response Unit (TRU)
The eSentire Threat Response Unit (TRU) is an industry-leading threat research team committed to helping your organization become more resilient. TRU is an elite team of threat hunters and researchers that supports our 24/7 Security Operations Centers (SOCs), builds threat detection models across the eSentire XDR Cloud Platform, and works as an extension of your security team to continuously improve our Managed Detection and Response service. By providing complete visibility across your attack surface and performing global threat sweeps and proactive hypothesis-driven threat hunts augmented by original threat research, we are laser-focused on defending your organization against known and unknown threats.
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