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Research by:Jiri Vinopal, Dennis Yarizadeh and Gil Gekker

Key Findings

While responding to a ransomware case against a US-based company, the CPIRT recently came across a unique ransomware strain deployed using a signed component of a commercial security product. Unlike other ransomware cases, the threat actor did not hide behind any alias and appears to have no affiliation to any of the known ransomware groups. Those two facts, rarities in the ransomware ecosystem, piqued CPR interest and prompted us to thoroughly analyze the newly discovered malware.

Throughout its analysis, the new ransomware exhibited unique features. A behavioral analysis of the new ransomware suggests it is partly autonomous, spreading itself automatically when executed on a Domain Controller (DC), while it clears the event logs of the affected machines. In addition, its extremely flexible, operating not only based on a built-in configuration but also on numerous optional arguments which allow it to change its behavior according to the operators needs. While it seems to have taken inspiration from some of the most infamous ransomware families, it also contains unique functionalities, rarely seen among ransomware, such as the use of direct syscalls.

The ransomware note sent out to the victim was formatted similarly to Yanluowang ransomware notes, although other variants dropped a note that more closely resembled DarkSide ransomware notes (causing some to mistakenly refer to it as DarkSide). Each person who examined the ransomware saw something a little bit different, prompting us to name it after the famous psychological test Rorschach Ransomware.

Execution Flow

As observed in the wild, Rorschach execution uses these three files:

Upon execution of cy.exe, due to DLL side-loading, the loader/injector winutils.dll is loaded into memory and runs in the context of cy.exe. The main Rorschach payload config.ini is subsequently loaded into memory as well, decrypted and injected into notepad.exe, where the ransomware logic begins.

Figure 1 Rorschachs High Level Execution Flow on both endpoints and on Domain Controllers.

Rorschach spawns processes in an uncommon way, running them in SUSPEND mode and giving out falsified arguments to harden analysis and remediation efforts. The falsified argument, which consists of a repeating string of the digit 1 based on the length of the real argument, rewritten in memory and replaced with the real argument, resulting in a unique execution:

Figure 2 Rorschachs process tree spawns processes with falsified arguments.

The ransomware uses this technique to run the following operations:

When executed on a Windows Domain Controller (DC), the ransomware automatically creates a Group Policy, spreading itself to other machines within the domain. Similar functionality was linked in the past to LockBit 2.0, although the Rorschach Ransomware GPO deployment is carried out differently, as described below:

Our colleagues in AhnLab published a more thorough behavioral analysis of another Rorschach variant which provides further details into the operations.

In addition to the ransomwares uncommon behavior described above, the Rorschach binary itself contains additional interesting features, differentiating it further from other ransomware.

The actual sample is protected carefully, and requires quite a lot of work to access. First, the initial loader/injector winutils.dll is protected with UPX-style packing. However, this is changed in such a way that it isnt readily unpacked using standard solutions and requires manual unpacking. After unpacking, the sample loads and decrypts config.ini, which contains the ransomware logic.

After Rorschach is injected into notepad.exe, its still protected by VMProtect. This results in a crucial portion of the code being virtualized in addition to lacking an IAT table. Only after defeating both of these safeguards is it possible to properly analyze the ransomware logic.

Although Rorschach is used solely for encrypting an environment, it incorporates an unusual technique to evade defense mechanisms. It makes direct system calls using the syscall instruction. While previously observed in other strains of malware, its quite startling to see this in ransomware.

The procedure involves utilizing the instruction itself, and it goes as follows:

In other words, the malware first creates a syscall table for NT APIs used for file encryption:

Figure 3 Creation of syscall table for certain NT APIs.

The end of the table is a section with the relevant syscall numbers:

Figure 4 Section containing the syscall table.

The example below shows how the syscall numbers are used:

Figure 5 Example use of direct syscall.

This obfuscated process is not required for the ransomware encryption logic, which suggests it was developed to bypass security solutions monitoring direct API calls.

In addition to the hardcoded configuration, the ransomware comes with multiple built-in options, probably for the operators comfort. All of them are hidden, obfuscated, and not accessible without reverse-engineering the ransomware. This table contains some of the arguments that we discovered:

This is only a partial list, with additional arguments suggesting networking capabilities, such as listen, srv and hostfile.

Example of how some of these arguments are used:

Before encrypting the target system, the sample runs two system checks that can halt its execution:

The Rorschach ransomware employs a highly effective and fast hybrid-cryptography scheme, which blends the curve25519 and eSTREAM cipher hc-128 algorithms for encryption purposes. This process only encrypts a specific portion of the original file content instead of the entire file. The WinAPI CryptGenRandom is utilized to generate cryptographically random bytes used as a per-victim private key. The shared secret is calculated through curve25519, using both the generated private key and a hardcoded public key. Finally, the computed SHA512 hash of the shared secret is used to construct the KEY and IV for the eSTREAM cipher hc-128.

Figure 6 The Rorschach hybrid-cryptography scheme.

Analysis of Rorschachs encryption routine suggests not only the fast encryption scheme mentioned previously but also a highly effective implementation of thread scheduling via I/O completion ports. In addition, it appears that compiler optimization is prioritized for speed, with much of the code being inlined. All of these factors make us believe that we may be dealing with one of the fastest ransomware out there.

To verify our hypothesis, we conducted five separate encryption speed tests in a controlled environment (with 6 CPUs, 8192MB RAM, SSD, and 220000 files to be encrypted), limited to local drive encryption only. To provide a meaningful comparison with other known fast ransomware, we compared Rorschach with the notorious LockBit v.3.

The result of the speed tests:

It turned out that we have a new speed demon in town. Whats even more noteworthy is that the Rorschach ransomware is highly customizable. By adjusting the number of encryption threads via the command line argument -thread, it can achieve even faster times.

When we compared Rorschach to other well-known ransomware families, we noticed that Rorschach uses a variety of time-honored methods together with some novel ideas in the ransomware industry. The name itself, Rorschach, is quite self-explanatory; with deep reverse engineering of the code and its logic, we found certain similarities with some of the more technically advanced and established ransomware groups.

We discussed Rorschachs hybrid-cryptography scheme in detail above, but we suspect that this routine was borrowed from the leaked source code of Babuk ransomware. See the following code snippets as examples:

Figure 7 Hybrid-cryptography scheme of Rorschach vs.Babuk.

Rorschachs inspiration from Babuk is evident in various routines, including those responsible for stopping processes and services. In fact, the code used to stop services through the service control manager appears to have been directly copied from Babuks source code:

Figure 8 Stopping predefined list of services Rorschach vs.Babuk.

It is also worth noting that the list of services to be stopped in Rorschachs configuration is identical to that in the leaked Babuk source code. However, the list of processes to be stopped differs slightly, as Rorschach omits notepad.exe, which is used as a target for code injection.

Rorahsach takes inspiration from another ransomware strain: LockBit. First, the list of languages used to halt the malware is exactly the same list that was used in LockBit v2.0 (although the list is commonly used by many Russian speaking groups, and not just LockBit). However, the I/O Completion Ports method of thread scheduling ****is another component where Rorschach took some inspiration from LockBit. The final renaming of the encrypted machine files in Rorschach is implemented via NtSetInformationFile using FileInformationClass FileRenameInformation, just like in LockBit v2.0.

Figure 9 Renaming of encrypted file using NtSetInformationFile.

As noted before, Rorschachs code is protected and obfuscated in a way that is unusual for ransomware, and is compiled with compiler optimization to favor speed and code inlining as much as possible. This makes finding similarities with other well-known ransomware families a real brain-buster. But we can still say that Rorschach took the best from the ransomware families with the highest reputation, and then added some unique features of its own.

As we noted, Rorschach does not exhibit any clear-cut overlaps with any of the known ransomware groups but does appear to draw inspiration from some of them.

We mentioned previously that Ahnlab reported a similar attack earlier this year. While it was carried out through different means, the ransomware described in the report triggers an almost identical execution flow. However, the resulting ransom note was completely different. The note was actually very similar to those issued by DarkSide, which probably led to this new ransomware being named DarkSide, despite the group being inactive since May 2021.

The Rorschach variant we analyzed leaves a different ransom note based on the structure used by Yanlowang, another ransomware group:

Figure 10 Ransom note from Rorschach.

Our analysis of Rorschach reveals the emergence of a new ransomware strain in the crimeware landscape. Its developers implemented new anti-analysis and defense evasion techniques to avoid detection and make it more difficult for security software and researchers to analyze and mitigate its effects. Additionally, Rorschach appears to have taken some of the best features from some of the leading ransomwares leaked online, and integrated them all together. In addition to Rorschachs self-propagating capabilities, this raises the bar for ransom attacks. The operators and developers of the Rorschach ransomware remain unknown. They do not use branding, which is relatively rare in ransomware operations.

Our findings underscore the importance of maintaining strong cybersecurity measures to prevent ransomware attacks, as well as the need for continuous monitoring and analysis of new ransomware samples to stay ahead of evolving threats. As these attacks continue to grow in frequency and sophistication, it is essential for organizations to remain vigilant and proactive in their efforts to safeguard against these threats.

Harmony Endpoint provides runtime protection against ransomware with instant automated remediation, even in offline mode.

When running on a machine infected with the Rorschach ransomware, Harmony Endpoint Anti-ransomware detected the encryption process in different folders, including modifications made to Harmony Endpoint honeypot files. It ran a ranking algorithm that provided a verdict identifying the process as a ransomware.

The following services are stopped through a GPO issued by Rorschach, probably to prevent conflicting write orders to Database files (and thus preventing encryption):

SQLPBDMSSQLPBENGINEMSSQLFDLauncherSQLSERVERAGENTMSSQLServerOLAPServiceSSASTELEMETRYSQLBrowserSQL Server Distributed Replay ClientSQL Server Distributed Replay ControllerMsDtsServer150SSISTELEMETRY150SSISScaleOutMaster150SSISScaleOutWorker150MSSQLLaunchpadSQLWriterSQLTELEMETRYMSSQLSERVER

The following processes are killed using a group policy (scheduled task) issued by Rorschach executing C:windowssystem32taskkill.exe. Some are likely terminated to prevent write conflicts, and some are security solutions:

wxServer.exewxServerView.exesqlmangr.exeRAgui.exesupervise.exeCulture.exeDefwatch.exehttpd.exesync-taskbarsync-workerwsa_service.exesynctime.exevxmon.exesqlbrowser.exetomcat6.exeSqlservr.exe

The following is a list of services, hardcoded in its configuration, to be stopped via the service control manager:

The following is a hardcoded list of directories and files to be omitted from encryption:

The following is a list of process names that during Rorschachs execution these names are compared to those running on the machine and killed if matched. This is done through a combination of CreateToolhelp32Snapshot, Process32FirstW, Process32NextW, OpenProcess, and TerminateProcess. There is some overlap and redundancy to the list of services killed via the service control manager.

Transferring its own files to each workstation:

Executing a scheduled task to run the attack:

**REDACTED**Administrador %LogonDomain%%LogonUser% InteractiveToken HighestAvailable PT10M PT1H false false IgnoreNew false false true true true false P3D 7 true true %Public%cy.exe run=**REDACTED**

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Rorschach A New Sophisticated and Fast Ransomware - Check Point Research