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The Wizard of Deception: Jupyter Infostealer

One can make a modest tweak to the attacker's PowerShell script to save the assembly to disk instead of loading it into memory.

 

Researchers recently discovered a new variant of SolarMarker, a malware family which is mostly transmitted using SEO manipulation to persuade people into downloading malicious documents. SolarMarker uses defense evasion to extract auto-fill data, saved passwords, and stored credit card information from victims' web browsers. It offers extra features which are unusual to be seen in info stealers, such as file transfer and command execution from a C2 server.

Jupyter packaged itself with legal executables when it was first detected towards the end of 2020. When it was run, it revealed a PowerShell script that had been obfuscated. The threat group is improving layers of stealth and obfuscation, such as loading the Jupyter Dynamic-Link Library (.DLL) into memory rather than writing the file to disk. Now, it is frequently packaged in massive Windows® installer packages (.MSI) which can reach 100 MB in size. 

To further conceal its motives, these packages are still integrated with legitimate software and signed with valid digital certificates. The installer will load and seek to install the bundled genuine application after installation. However, buried deep within the Trojan installer's code is a small, extensively obfuscated, and encrypted PowerShell script which runs in the background. 

Jupyter has masked itself as a variety of programs and installers. The malware's main file extension has been changed to.MSI, and it executes its obfuscated PowerShell script via several techniques. Jupyter is usually hosted on phony downloading websites which pose as real hosts. These websites typically offer a free PDF book. These can be accessed accidently by a victim or via a link in a spam email. 

It is often packaged with freeware software and certified with unrevoked digital certificates, making the installation appear more authentic. When the Windows installer package is loaded, it will present an installer pop-up for the targeted legitimate application, while loading data and running in the background. 

Jupyter has deployed itself in a variety of ways in the past campaign. The malware usually has two primary files: 
  • An executable and a Windows PowerShell script that contains the harmful code.
  • Some Jupyter variants have also dumped a temporary file (.TMP) into the victim’s %AppData%\Roaming\Temp\ directory, to construct the normal content of Jupyter's main malicious PowerShell script. 

PowerShell is used by the virus to conceal and execute its harmful code without ever publishing itself to disk on the victim's PC. It avoids writing to disk by loading Jupyter's DLL into memory reflectively. DLLs are usually injected into a process from a file written to a disk. 

Reflective DLL injection is a technique for injecting code into a victim process directly from memory rather than from disk. Because the fully un-obfuscated malware does not live on disk, it necessitates the creation of a persistence mechanism, such as registry keys that reload the malware when the victim machine boots up. As a result, Jupyter DLL is difficult to both identify and use. 

Jupyter's basic PowerShell may be split down into six different phases or components. Each phase aids in the achievement of a given objective, function, or capability. Though many Jupyter samples follow the same procedures, differences in Jupyter's PowerShell code exist, and certain samples have been observed to work in slightly different methods to achieve the same goals. 

One can make a modest tweak to the attacker's PowerShell script to save the assembly to disk instead of loading it into memory. This will also assist us in comprehending the operation of this version of SolarMarker. One can see the decompiled code, as well as the names of the classes and functions, are incorrect. Instead, they appear to be obfuscated. 

The SolarMarker backdoor is a.NET C2 client which uses an encrypted channel to interact with the C2 server. HTTP is used for communication, with POST requests being the most common. The data is secured with RSA encryption and symmetric encryption using the Advanced Encryption Standard (AES). Internal reconnaissance is carried out by the client, who gathers basic information about the victim's system and exfiltrates it through an existing C2 channel. The infostealer module has a structure that is quite identical to the backdoor module we discussed earlier, but it has more features.

By reading files relevant to the target browser, the SolarMarker infostealer module obtains login data, cookies, and web data (auto-fill) from web browsers. To decrypt the credentials, SolarMarker uses the API method CryptUnprotectData (DPAPI). 

The usefulness of behavior-based detectors in reducing the stay time of threats inside a network has been recognized by the security industry in recent years. 
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