Uncovering the “Serpent” – K7 Labs

Information Stealers are a pervasive threat and are capable of providing threat actors with a rich source of sensitive data. 

Recently, we came across this tweet that the Serpent Stealer is on sale on the dark web. A .NET based malware, this has the ability to not only acquire sensitive information from the most popular online browsers and applications but also has the capability to exfiltrate  passwords.  

To stay stealth, the stealer bypasses Windows User Access Control (UAC), debuggers, and virtual machines. It exfiltrates the browser data and passwords via Web hooks and Discord abuse. 

Binary Analysis

Serpent is a .Net based stealer that utilises the .NET runtime. It is a 64-bit portable executable binary.

The procedures within the Main() function of the malware binary, employed for data theft, has been systematically presented below based on their execution sequence.

Environment checks

The stealer determines whether it is being run in a controlled environment on its first execution. It does that by checking whether the victim’s username-obtained exists in its “Black List Users” file.

The usernames that are blocked are shown in the table below. The stealer will instantly utilise the Sleep and Exit function to end its execution if any of the below usernames are obtained.

Data collection

Once the malware verifies that it is not running under a controlled environment, it starts collecting data for exfiltration.

It begins with obtaining autofill information. The directory “%Localappdata%GoogleChromeUser Data ” is first obtained. After that it establishes connection with the SQLite database and collects data using the “SELECT * FROM autofill” query.

Next it collects history data from “%Localappdata%GoogleChromeUser data” path. After that it establishes connection with the SQLite database and collects data using the “SELECT url FROM urls” query.

After this, it verifies the machine’s remote IP address. Then, it uses a webhook to exfiltrate the data it has collected to the C2 server.

After communicating with C2 it tries to collect password data from any existing browser like Chrome, Brave or Edge browsers.

Next it targets crypto wallets by collecting some well-known crypto wallet software data.

After collecting wallet data, it tries to collect bookmark data from Chrome browser,

Afterward, the malware extracts login credentials from the installation path by identifying the registry path associated with Steam, a video game digital distribution service.

It also tries to steal SSH credentials from ‘.ssh’ directory and FTP credentials from the windows registry.

At last it runs a file stealer, which targets some specific extensions from some specific folders in the file system.

The file stealer program target following directories,

• Desktop
• Documents
•  Pictures
• Videos
• Downloads

UAC Bypass

Before exiting, stealer calls one of the UAC bypass methods listed below

• GUI based Bypass
• Bypass using Fodhelper
•  Bypass using windows defender

Here, in the sample analysed,  they are using Fodhelper method,

Fodhelper.exe is a known UAC bypass method, and when it runs, it looks for certain registry keys that do not exist. As a result, a hacker can insert malicious commands into these registry keys to be executed by the fodhelper.exe with the highest privilege(Admin privilege). 

1. “New-Item “HKCU:SoftwareClassesms-settingsShellOpencommand” -Force” – This command creates a new registry key at the mentioned path in the registry.
2. “New-ItemProperty -Path “HKCU:SoftwareClassesms-settingsShellOpencommand” -Name “Delegate Execute” -Value “” -Force” – This command adds a new registry entry named Delegate Execute with an empty string value to the key.
3. “New-ItemProperty -Path “HKCU:SoftwareClassesms-settingsShellOpencommand” -Name “(default)” -Value ”{0}” -Force” – This command sets the default value of the registry key in the mentioned path to the value specified in the {0} placeholder.

As we can see, threat actors use advanced stealth techniques in info stealers to become more evasive. As the information stolen by the malware is sensitive, protecting yourself by investing in a reputable security product is therefore necessary in today’s world. We at K7 Labs provide detection for such kinds of stealers and all the latest threats. Users are advised to use a reliable security product such as “K7 Total Security” and keep it up-to-date to safeguard their devices.

IOCs