| Title | Author | Created | Published | Tags | | ---------------------- | ---------- | ------------------ | ------------------ | ---------------------------- | | StealC - Detailed Info | Jon Marien | September 24, 2025 | September 24, 2025 | [[#issessions\|#issessions]] | --- # StealC - Detailed Info --- From my perspective, StealC is a classic example of how malware-as-a-service has lowered the barrier to entry for cybercrime. It's a copycat, borrowing heavily from other successful info-stealers like Vidar and Raccoon, but its rapid development and the addition of features like RC4 encryption show that its developers are actively trying to stay ahead of security researchers. The BlockBlasters incident is a textbook case of a supply chain attack, and it's a stark reminder that even seemingly legitimate software from trusted platforms can be a vector for malware. Key Points: - What is StealC? A popular information stealer sold as a Malware-as-a-Service (MaaS) on Russian-speaking underground forums. - How does it work? It infects systems and steals sensitive information like browser data, cryptocurrency wallets, and application credentials. - The BlockBlasters Incident: A recent example of StealC being distributed through a compromised game on Steam. - StealC V2: An updated version with enhanced features like RC4 encryption, expanded payload delivery, and a redesigned control panel. ## In-depth Analysis: ### The StealC Malware Family Bottom Line Up Front (BLUF): StealC is a dangerous and evolving information stealer that poses a significant threat due to its accessibility and sophisticated features. StealC is a relatively new but already popular information stealer that emerged in early 2023. It's sold as a MaaS, which means that aspiring cybercriminals can purchase access to the malware and its supporting infrastructure without needing to have advanced technical skills. This has led to its widespread use in various campaigns. The malware is written in C++ and is designed to be highly effective at stealing a wide range of sensitive information. It targets data from popular web browsers, cryptocurrency wallets (both browser-based and desktop applications), and various other applications like FTP clients and email clients. #### **The BlockBlasters Incident: A Case Study** BLUF: The BlockBlasters incident demonstrates how StealC can be effectively distributed through a Trojan horse strategy, using a legitimate-looking application to deliver the malicious payload. The incident involving the Steam game "BlockBlasters" is a perfect illustration of how StealC is being used in the wild. The attackers first published a clean version of the game to build trust and garner positive reviews. Then, they pushed an update that contained the StealC malware. This is a classic supply chain attack, and it's a very effective way to bypass security measures. The forensic report from vx-underground provides a wealth of technical details about the malware used in this attack. It shows that the malware was designed to steal cryptocurrency, and it even included a list of specific individuals to target. The report also details how the attackers' C2 server was taken down by security researchers. ### StealC V2: What's New? BLUF: StealC V2 is a significant upgrade over the original version, with new features that make it more stealthy and effective. The developers of StealC are constantly working to improve their malware. StealC V2, which was released in March 2025, includes several key enhancements: - RC4 Encryption: The malware now uses RC4 encryption to protect its network communications, making it harder for security tools to detect and analyze. - Expanded Payload Delivery: StealC V2 can now deliver a wider range of payloads, including MSI packages and PowerShell scripts. - Redesigned Control Panel: The new control panel gives attackers more control over their operations, with features like the ability to customize payload delivery rules based on the victim's location or the software they have installed. - Enhanced Data Theft: StealC V2 has a new "unified file grabber" that can steal data from a wider range of applications. --- While StealC is a formidable threat, it's not operating in a vacuum. It's part of a larger ecosystem of information stealers, each with its own strengths and weaknesses. Understanding these differences is key to developing effective defense strategies. The recommendations I've provided are not just about avoiding malware; they're about building a security-conscious mindset that can help protect against a wide range of threats. | **Feature** | **StealC** | **Vidar** | **Raccoon** | **RedLine** | | ---------------------- | -------------------------------------------------------------------- | ------------------------------------------------------ | ------------------------------------------------------ | -------------------------------------------------------------------------- | | **Origin** | Malware-as-a-Service (MaaS) on Russian-speaking forums | MaaS, first seen in 2018 | MaaS, first seen in 2019 | MaaS, first seen in 2020 | | **Distribution** | Social engineering, malvertising, compromised software (e.g., games) | Malvertising, phishing emails, exploit kits | Phishing emails, exploit kits, Telegram | Phishing campaigns, YouTube, Discord | | **Data Stolen** | Browser data, crypto wallets, FTP clients, email clients | Browser data, crypto wallets, FTP clients, screenshots | Browser data, crypto wallets, system information | Browser data, crypto wallets, FTP clients, VPN clients, system information | | **C2 Communication** | JSON over HTTP, RC4 encryption (in V2) | HTTP, may use Telegram for C2 | HTTP, string encryption | SOAP-based protocol over HTTP/HTTPS | | **Evasion Techniques** | Anti-VM checks (in V1), string obfuscation, Themida packing | Anti-VM/sandbox checks, string encryption | Anti-analysis techniques, dynamic loading of libraries | String encryption, anti-debugging techniques | ## For Gamers: - Be Wary of Game Updates: As seen with the BlockBlasters incident, even legitimate games can be compromised. Be cautious of unexpected updates, especially if they are not from the official platform (e.g., Steam, Epic Games Store). - Avoid Pirated Games: Pirated games are a common vector for malware. Only download games from official and reputable sources. - Use a Standard User Account: Avoid using an administrator account for gaming. This can limit the damage a malware infection can cause. - Keep Your System and Software Updated: Regularly update your operating system, web browser, and other software to patch security vulnerabilities. - Use a Reputable Antivirus: A good antivirus can detect and block many types of malware, including cryptostealers. ## For Cryptocurrency Users: - Use a Hardware Wallet: A hardware wallet is the most secure way to store your cryptocurrency. It keeps your private keys offline, making them inaccessible to malware. - Be Wary of Phishing Attacks: Phishing attacks are a common way for cybercriminals to steal cryptocurrency. Be suspicious of unsolicited emails, messages, and links, especially if they ask for your private keys or other sensitive information. - Use a Separate Device for Crypto Transactions: If possible, use a dedicated device for managing your cryptocurrency. This can help to isolate your crypto assets from potential malware infections on your primary device. - Enable Two-Factor Authentication (2FA): Enable 2FA on all of your cryptocurrency accounts. This adds an extra layer of security, making it more difficult for attackers to gain access to your accounts. - Do Your Own Research (DYOR): Before investing in any cryptocurrency project, do your own research to ensure it is legitimate. Be wary of projects that promise unrealistic returns or use high-pressure sales tactics. ---