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In a world where cyber threats evolve faster than defenses, a new malware variant called PupkinStealer has surfaced, showcasing how modern information stealers are becoming more efficient, covert, and harder to detect. Developed in C and running on the .NET framework, this malware has been uncovered by researchers at CYFIRMA. It leverages popular platforms like Telegram not just for command and control (C2) but also for quietly exfiltrating stolen data without raising red flags.
PupkinStealer marks a disturbing trend in cybercrime—favoring stealth and speed over complex evasion techniques. Its modular structure and swift execution pipeline make it a formidable threat, especially for users and organizations lacking advanced endpoint protection. Here’s a detailed breakdown of how it works, who it targets, and what defenders can do about it.
Understanding PupkinStealer: A 30-Line Digest
What It Is: PupkinStealer is a new malware designed for stealing sensitive user data—credentials, documents, session tokens, and screenshots—while maintaining a low operational footprint.
Built Using: Developed in C on the .NET framework, a popular choice for flexibility and rapid deployment.
Primary Goal: Instead of persistence or self-protection, PupkinStealer is engineered for fast, focused data theft and covert exfiltration.
Entry Point: Once executed, it launches asynchronous processes that work in parallel to steal a wide variety of user data.
Browser Credential Theft: Targets Chromium-based browsers (e.g., Chrome, Edge, Opera) by extracting and decrypting stored login credentials.
How It Steals: Uses Windows Data Protection API to decrypt sensitive fields, enabling access to stored passwords.
File Targeting: Actively searches for files with sensitive extensions like .pdf, .txt, .sql, .jpg, and .png on the desktop.
Silent Operation: Avoids crashes or alerts by quietly bypassing errors—helping it run smoothly without drawing attention.
Telegram Hijacking: Copies session data from Telegram’s “tdata” folder, enabling attackers to hijack accounts without credentials.
Discord Tokens: Scrapes local leveldb databases using regular expressions to find Discord authentication tokens.
Screenshot Capability: Captures high-resolution screenshots (1920×1080), providing visual context about the victim’s environment.
Data Packaging: All stolen data is zipped into a single archive, which includes the user’s public IP, Windows SID, and other metadata in the ZIP comment field.
Exfiltration Route: Uses Telegram’s Bot API to send the stolen ZIP file directly to the attacker’s chat ID, bypassing traditional detection methods.
Attribution: Research suggests a Russian-speaking developer named “Ardent” is behind this malware, based on embedded code and Telegram bio strings.
Bot Token Observed: Includes a hardcoded bot token and chat ID in its exfiltration URL—making detection and blocking possible with the right tools.
Malware-as-a-Service (MaaS): Reflects the growing trend of commoditized malware offerings where attackers use pre-built tools.
No Persistence: Doesn’t install itself permanently or resist analysis—once it finishes its job, it disappears.
Low Complexity, High Efficiency: It’s not sophisticated in a traditional sense, but it’s highly optimized for its task.
Avoiding Detection: By using Telegram, it masks traffic under normal messaging behavior, reducing the risk of being flagged by firewalls or intrusion systems.
Preventative Advice: Organizations are urged to deploy strong Endpoint Detection and Response (EDR), monitor outbound Telegram traffic, and train employees on phishing awareness.
File Path Patterns: Uses consistent paths for storing stolen data temporarily before exfiltration—useful for identifying infections.
Key Indicators: Includes file hashes, Telegram bot tokens, and data collection paths that can help threat hunters detect infections.
Recommendations: Whitelisting, behavioral monitoring, and software updates are crucial for minimizing risk.
Rising Threat: PupkinStealer is part of a broader wave of lightweight infostealers emphasizing modularity and simplicity over complexity.
Human Risk Factor: User education remains vital—most infections begin with someone clicking or opening something they shouldn’t.
What Undercode Say:
PupkinStealer is not just another malware in the wild—it’s a manifestation of how cybercriminal tactics are evolving to become more streamlined and effective. It leverages every shortcut available: Telegram for command and control, C for rapid development, and familiar targets like browsers and chat apps for quick wins. The malware is particularly clever in its ability to avoid traditional detection, relying on legitimate-looking outbound traffic that’s less likely to trigger alarms.
One of the more sophisticated components of this stealer is its approach to credential extraction. Instead of blindly grabbing encrypted blobs, it goes the extra mile to decrypt them using native Windows APIs, ensuring the stolen data is immediately useful to the attacker. This makes it highly dangerous in corporate environments where saved browser credentials might include access to sensitive internal portals or cloud services.
The file targeting strategy is another key concern. By scraping common document and image filetypes, PupkinStealer maximizes its chances of harvesting valuable information—intellectual property, contracts, blueprints, or personal photos—without needing deep system access.
The Telegram and Discord session hijacking adds another layer of severity. These platforms are increasingly used in business communications and even for developer collaboration, meaning stolen sessions can result in unauthorized access to both personal and organizational conversations and assets.
The malware’s use of ZIP archiving and detailed metadata tagging makes it highly scalable. From an attacker’s perspective, sorting through stolen data becomes easier, enabling faster monetization or targeted extortion campaigns. The ZIP file’s embedded details—usernames, IPs, and system IDs—essentially create a fingerprint of the victim, ready for exploitation.
Yet perhaps most alarming is the minimalistic nature of the malware. It doesn’t try to install itself deeply into the system, doesn’t persist across reboots, and doesn’t waste resources on evasion. It’s a hit-and-run tool, optimized for one job: data theft.
This “get in, get out” philosophy is emblematic of the modern threat landscape. Malware authors are increasingly favoring disposable, modular tools that can be easily repackaged or sold on the dark web. PupkinStealer’s structure suggests it could be part of a malware-as-a-service (MaaS) ecosystem, where cybercriminals rent or purchase access to tools like these for quick campaigns.
For defenders, the takeaway is clear: traditional antivirus is no longer enough. Behavioral monitoring, traffic analysis (especially around Telegram), and comprehensive user training must become baseline security practices. The fact that this stealer doesn’t even try to maintain persistence suggests that many users might already be compromised without ever realizing it.
It’s also
References:
Reported By: cyberpress.org
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