Executive Summary

A new Python-based information stealer, VVS Stealer, is being actively marketed on Telegram and deployed against users of the popular communication platform Discord. The malware's primary innovation is its use of PyArmor, a legitimate commercial-grade Python code obfuscator, to encrypt its payload. This technique makes the malware extremely difficult to analyze using static methods and allows it to evade many signature-based antivirus products. VVS Stealer is a comprehensive credential thief, designed to extract Discord authentication tokens, browser data (cookies, passwords, history), and inject malicious JavaScript into the Discord client to capture credentials in real-time. The stolen data is then exfiltrated via Discord webhooks, leveraging a trusted service to bypass network security controls.

Threat Overview

VVS Stealer is part of the growing Malware-as-a-Service (MaaS) ecosystem, offered on Telegram with subscriptions starting as low as €10. This low barrier to entry allows even unsophisticated actors to deploy capable stealer malware. The primary targets are Discord users, often gamers or members of cryptocurrency communities, who are tricked into downloading and running the malicious executable.

The malware's use of PyArmor is a significant technical feature. PyArmor is designed to protect Python scripts from reverse engineering, but here it is abused to conceal the stealer's malicious functions from security software. This forces defenders to rely on behavioral analysis and runtime detection rather than static signatures.

Once executed, VVS Stealer performs several malicious actions:

• Establishes persistence in the Windows Startup folder.
• Scans for and decrypts Discord tokens using the Windows Data Protection API (DPAPI).
• Injects malicious JavaScript into the Discord client to intercept password changes.
• Steals cookies, passwords, and other data from Chromium- and Firefox-based browsers.
• Exfiltrates all collected data to an attacker-controlled Discord webhook.

Technical Analysis

The attack chain for VVS Stealer is typical for an info-stealer, but with an emphasis on evasion.

1. Initial Access (T1566.001 - Spearphishing Attachment): The malware is typically distributed as a malicious file disguised as a game cheat, mod, or other desirable software, often sent via a Discord message.
2. Defense Evasion (T1027 - Obfuscated Files or Information): This is the key step. The core Python script is packed and obfuscated using PyArmor. The final executable is a loader that decrypts and runs the malicious Python code in memory.
3. Persistence (T1547.001 - Registry Run Keys / Startup Folder): The malware copies itself to the %APPDATA%\Microsoft\Windows\Start Menu\Programs\Startup folder to ensure it runs every time the user logs in.
4. Credential Access (T1555.003 - Credentials from Web Browsers): The stealer queries the local SQLite databases used by browsers like Chrome and Edge to steal cookies and saved logins.
5. Credential Access (T1528 - Steal Application Access Token): The malware specifically searches for Discord token files. It uses the user's DPAPI key to decrypt the tokens, giving the attacker full access to the victim's Discord account.
6. Defense Evasion (T1056.004 - Credential API Hooking): By injecting JavaScript into Discord's process, it hooks network requests to capture password changes before they are sent to Discord's servers.
7. Exfiltration (T1567.002 - Exfiltration to Web Service): All stolen data is bundled and sent via an HTTP POST request to a Discord webhook URL hardcoded in the malware.

Impact Assessment

• Account Takeover: Victims lose control of their Discord accounts, which can be used to defraud friends, spread the malware further, or sell valuable accounts (e.g., those with rare badges).
• Financial Loss: Stolen browser cookies can be used to bypass MFA and access online banking, cryptocurrency exchanges, and other financial accounts.
• Identity Theft: The combination of stolen credentials and personal information from various sources can lead to comprehensive identity theft.
• Further Compromise: Stolen credentials for one service are often reused elsewhere, allowing attackers to compromise a victim's entire digital life.

Cyber Observables for Detection

• Execution of Python interpreters (python.exe) from unusual locations or by unexpected parent processes.
• Network connections to discord.com/api/webhooks/ from processes other than the official Discord client.
• Modifications to the files within Discord's application data folders (%APPDATA%\discord\).

Detection & Response

• Behavioral Analysis: Since static analysis is defeated by PyArmor, detection must focus on behavior. An EDR solution that monitors process behavior is key. It should alert on a new executable dropping a file in the Startup folder, accessing browser credential stores, and making outbound connections to a Discord webhook. This is an application of D3-PA: Process Analysis.
• Network Traffic Analysis: Monitor all outbound HTTP/S traffic. Even if the payload is encrypted, the destination URL for the Discord webhook is often in plaintext. Block all connections to discord.com/api/webhooks/ from endpoints that are not explicitly authorized to use them. This aligns with D3-OTF: Outbound Traffic Filtering.
• Memory Scanning: Advanced EDR or antivirus tools can perform in-memory scanning to detect the malicious Python code after it has been decrypted by the PyArmor loader.

Mitigation

• User Education: The primary defense is to not run executables from untrusted sources. Users should be warned about the dangers of downloading game cheats, cracks, or other suspicious files, especially those sent by strangers on Discord.
• Principle of Least Privilege (User Accounts): Running as a standard user without administrative privileges can limit the malware's ability to establish persistence or inject into certain system processes.
• Password Manager: Encourage the use of a password manager. While this doesn't stop cookie theft, it prevents the theft of a master list of passwords stored in the browser's built-in manager.
• Application Whitelisting: In a corporate environment, use application whitelisting (D3-EAL: Executable Allowlisting) to prevent any unauthorized executables from running, regardless of whether they are detected as malicious.