Tag: Threat Analysis

Arechclient2 Malware Analysis (sectopRAT)

Anurag Gawande8 Comments

Overview

Arechclient2, also known as sectopRAT, is a Remote Access Trojan (RAT) written in .NET. This malware is highly obfuscated using the calli obfuscator, making its analysis challenging. Despite attempting deobfuscation using calliFixer, the code remained obfuscated but was still somewhat readable using dnSpy.

The sample analyzed has the following characteristics:

File Hash: EED3542190002FFB5AE2764B3BA7393B
File Size: 768KB
Original File Name: Bluefin.exe
File Type: .Net
Obfuscation Technique: calli obfuscator
Mutex Name: 49c5e6d7577e447ba2f4d6747f56c473
VT Detection: 61/72
File Download: any.run

Static Analysis

Obfuscation Technique

The malware is obfuscated using the calli obfuscator, as identified using Detect It Easy (DIE).

Attempts to deobfuscate the code using CalliFixer were unsuccessful, as shown below:

Extracted Strings

Extracting strings from the executable revealed significant indicators of the malware’s capabilities. Some of the key strings found include:

  • Browser Data Extraction: URL, User, Password0, AccountT, BrowserExtension, AutofillT, Logins, Cookies7, os_crypt, LocalState, encrypted_key
  • System and Hardware Information: HardwareType, OSVersion, Machine, ReleaseID, Language, ScreenSize, TimeZone, IPv4, Monitor
  • Installed Software and Processes: AvailableLanguages, Softwares, Processes, SystemHardwares
  • Targeted Applications and Services: Nord, Open, Proton (VPNs), Steam, Discord, Telegram, FTP, ScanBrowsers, ScanFiles, ScanFTP, ScanWallets, ScanScreen
  • Data Exfiltration and Storage: FileLocation, SeenBefore3, FileScannerArgT, OfApplication, Directory, Pattern, Recoursive7

Observed Functionalities

Upon analyzing the decompiled code, several key functionalities were observed:

  • Scanning and gathering information about installed web browsers, including browser extensions and stored credentials.
  • Extracting cookies, usernames, passwords, and autofill data.
  • Scanning the system for installed VPN services such as NordVPN and ProtonVPN.
  • Collecting system information, including hardware details and OS specifications.
  • Looking for installed game launchers, Telegram, and Discord configurations.
  • Scanning for FTP connections and stored credentials.
  • Searching for wallet configurations, indicating potential interest in cryptocurrency theft.

Dynamic Analysis

Upon execution in a controlled environment, the malware exhibited network-based behaviors, connecting to a remote Command and Control (C2) server:

  • C2 Server IP: 91.202.233.18
  • Port: 9000
  • Port:15647

  • Downloaded Files:
    • manifest.json (Defines the extension’s name, permissions, and scripts)
    • content.js (Core malicious script for keylogging and data theft)
    • background.js (Bypasses security restrictions and transmits stolen data)

Malicious Chrome Extension Disguised as “Google Docs”

The downloaded files are part of a Google Chrome extension masquerading as “Google Docs.” This extension is a stealthy data-stealing tool designed to exfiltrate user input across all websites. The files were retrieved from the following URL:

  • Download URL: http://91.202.233[.]18:9000/wbinjget?q=9A7A4DFA51C1DFA51C1DFC689A43860F0BECA70

Its functionality is split across three key files:

  • manifest.json
    • Declares the extension’s name and description (misleading claim of Google Docs offline editing)
    • Grants broad permissions, including , allowing script injection across all web pages
  • content.js
    • Injects event listeners into every webpage
    • Monitors and captures all user input fields (textboxes, checkboxes, dropdowns, buttons, text areas)
    • Sends recorded data, including usernames, passwords, credit card details, and form data, along with the URL to the attacker’s server
  • background.js
    • Acts as a middleman to bypass browser security policies
    • Uses browser permissions to make unauthorized HTTP requests to an external attacker-controlled server
    • Relays stolen data from content.js to the remote server
Installed Google Chrome Extension
Dropped JavaScript code and Json file.

Additionally, during debugging, it was observed that the malware connects to an external URL:

  • URL: https://pastebin.com/raw/wikwTRQc
  • Sandbox Analysis: The webpage at this URL contains the same IP (91.202.233.18)

Further Payload Analysis

During analysis, no additional payloads were observed being dropped or executed. However, given the RAT’s capabilities and network behavior, it is possible that further payloads may be delivered dynamically by the C2 server depending on the victim’s environment.

Indicators of Compromise (IoCs)

File Hashes

  • EED3542190002FFB5AE2764B3BA7393B

C2 Servers

  • 91.202.233.18:9000
  • 91.202.233.18:15647

Malicious URLs

Mutex

  • 49c5e6d7577e447ba2f4d6747f56c473

Security Implications

This malicious extension operates as a coordinated data-harvesting tool, capturing nearly all user input and exfiltrating it to a remote C2 server. The misleading name, broad web access, and ability to evade browser security make it a severe threat.

Recommendations:

  • Block network traffic to 91.202.233.18:9000 and 91.202.233.18:15647.
  • Monitor %AppData%/Local/llg for suspicious file creations.
  • Remove any unknown Chrome extensions, particularly those masquerading as Google Docs.
  • Use behavioral-based threat detection to identify suspicious activities.
  • Restrict execution of untrusted .NET applications.

This analysis highlights the evolving threats posed by obfuscated RATs and malicious browser extensions, emphasizing the need for enhanced security monitoring and strict browser extension controls.

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NanoCore RAT Malware Analysis

Anurag Gawande1 Comment

NanoCore is a well-known Remote Access Trojan (RAT) used by threat actors for espionage, data theft, and system control. In this post, I will analyze a NanoCore RAT sample with the hash 18B476D37244CB0B435D7B06912E9193 and explore its behavior, obfuscation techniques, and deobfuscation process.

File Hash MD5: 18B476D37244CB0B435D7B06912E9193
Filename: Sigmanly_0bbff62a45fc9776575ed143af2d7db332e2781d7e3de56eb3ff48c25d0c7b46
File size: 203.00 KB
NanoCore Client Version: 1.2.2.0
VirusTotal Detection Score: 64/72
File download: any.run

Static Analysis

Initial Inspection

Using Detect It Easy (DIE), I identified that the sample is a .NET executable and employs Eazfuscator obfuscation to hinder analysis.

Deobfuscation

To analyze the code effectively, I used de4dot to deobfuscate the executable. de4dot successfully restored readable class and method names, making it easier to understand the malware’s logic.

Below is how the deobfuscated code appears now.

Strings Analysis

Using SysInternals Strings, I extracted various strings from the binary and found the following indicators:

  • “Connecting to {0}:{1}..”
  • “/create /f /tn “{0}” /xml “{1}””
  • “schtasks.exe”
  • “CreateScheduledTask”
  • “/run /tn “{0}””
  • “RunScheduledTask”
  • “Host: {0}”

These strings indicate that the malware uses Windows Task Scheduler for persistence and C2 communication.

Dynamic Analysis

To gain deeper insights, I used dnSpy to debug the code and analyze its behavior in a controlled environment.

Execution Flow Analysis

Startup Routine: NanoCore attempts to achieve persistence by copying itself to a hidden directory and creating a registry entry.

  • During dynamic analysis, I found that it adds saasmon.exe under the HKCU\Software\Microsoft\Windows\CurrentVersion\Run registry key.
  • It also creates a folder at C:\Program Files (x86)\SAAS Monitor to store its components.
  • Another folder is created at C:\Users\User\AppData\Roaming\81E42A3A-6BA0-4784-B7EC-E653E9E1A8ED, where the SAAS Monitor folder is placed, and saasmon.exe is dropped.

C2 Communication: The RAT connects to a remote Command-and-Control (C2) server, enabling an attacker to issue commands.

  • Wireshark Analysis: The malware attempts to establish connections to:
    • simpletest.ddns.net (Potential C2 domain)
    • 8.8.8.8 (Google DNS, likely used for connectivity checks)
    • Uses port 9632 to communicate with the given IP.
  • Plugin System: NanoCore features a modular plugin system, allowing attackers to load additional capabilities dynamically.
  • Installed Plugins: During dynamic analysis, I found that NanoCore installed the SurveillanceEx plugin, which enhances its spying capabilities.

  • Data Exfiltration: Captures keystrokes, screenshots, and clipboard data, sending them to the attacker.
  • It stores keylogs and clipboard data in C:\Users\User\AppData\Roaming\81E42A3A-6BA0-4784-B7EC-E653E9E1A8ED\logs\users\kbxxxxx.dat.

In the image above, you can see that it is storing clipboard data along with the commands and text I was entering in applications.

Task Scheduler Analysis: The code contains functions to create a scheduled task using schtasks.exe, but during dynamic analysis, no scheduled task was actually created. Below is an image of the relevant code snippet that shows its intent to use Task Scheduler for persistence.

Indicators of Compromise (IOCs)

  • File Hash: 18B476D37244CB0B435D7B06912E9193
  • Network Indicators: (Extracted from dynamic analysis)
    • C2 Domain: simpletest.ddns.net
    • IP Contacted: 8.8.8.8 (Google DNS, may be used for connectivity checks)
    • Port: 9632
  • Registry Changes:
    • HKCU\Software\Microsoft\Windows\CurrentVersion\Run\saasmon.exe
  • File System Changes:
    • C:\Program Files (x86)\SAAS Monitor\saasmon.exe
    • C:\Users\User\AppData\Roaming\81E42A3A-6BA0-4784-B7EC-E653E9E1A8ED\SAAS Monitor\saasmon.exe
    • C:\Users\User\AppData\Roaming\81E42A3A-6BA0-4784-B7EC-E653E9E1A8ED\logs\users\kbxxxxx.dat (Stores keylogs and clipboard data)

Conclusion

NanoCore RAT remains a persistent threat due to its modularity and extensive feature set. Through deobfuscation with de4dot and debugging with dnSpy, I was able to uncover its core functionalities. Defenders should stay vigilant by leveraging threat intelligence, monitoring network traffic, and applying proactive security controls.

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