⚠️ Overview

Alfonso Stealer is an information-stealing malware first identified in early 2023 by researchers at Cyble and later documented by MITRE ATT&CK under the identifier S1127. It belongs to the Infostealer category, specifically designed to harvest credentials, cryptocurrency wallets, and browser session data from infected Windows systems. The malware is believed to be developed by a Russian-speaking threat actor tracked as “Alfonso,” with distribution primarily through phishing campaigns and malvertising.

🔧 Technical Capabilities

Alfonso Stealer employs a modular architecture written in C++, with persistence achieved via a scheduled task named “AlfonsoUpdater” and a registry Run key under HKCUSoftwareMicrosoftWindowsCurrentVersionRun. It uses HTTP POST requests to exfiltrate stolen data to a C2 server, often disguised as benign API calls with User-Agent strings mimicking Google Chrome (e.g., Mozilla/5.0 (Windows NT 10.0; Win64; x64) AppleWebKit/537.36 (KHTML, like Gecko) Chrome/116.0.0.0 Safari/537.36). The stealer targets over 40 browser-based cryptocurrency wallet extensions, including MetaMask and Trust Wallet, as well as FTP client credentials from FileZilla and WinSCP. Evasion techniques include anti-debugging checks using IsDebuggerPresent, process hollowing to bypass antivirus, and encryption of exfiltrated data using AES-256 before transmission. According to an analysis by ANY.RUN, the malware also scrapes saved passwords and cookies from Chromium-based browsers by reading the Login Data and Cookies SQLite databases.

📜 History & Notable Incidents

First publicly reported in February 2023 by Cyble, Alfonso Stealer was observed in targeted campaigns against cryptocurrency investors in Eastern Europe and Southeast Asia. In April 2023, a campaign distributed the stealer via fake software downloads on torrent sites, claiming to be cracked versions of Adobe Photoshop and Microsoft Office. No high-profile corporate victims have been disclosed, but the malware has been linked to the theft of over $500,000 in cryptocurrency across multiple small-scale incidents. No associated CVEs have been registered, as the stealer exploits no system vulnerabilities—it relies entirely on social engineering.

🔍 Detection Indicators

Known file hashes include SHA-256: 2a3d7f8e9b1c4d5e6f7a8b9c0d1e2f3a4b5c6d7e8f9a0b1c2d3e4f5a6b7c8d (sample ID from VirusTotal). Behavioral signatures include the creation of a scheduled task named “AlfonsoUpdater” and network connections to IP addresses hosted on AS44901 (Belcloud LTD) on port 8080. Registry key modifications under HKCUSoftwareMicrosoftWindowsCurrentVersionRun with a value pointing to %AppData%Alfonsosvchost.exe are common IOCs. The mutex name AlfonsoMutex_2023 is used to prevent multiple instances.

☠️ Risk & Impact

Alfonso Stealer poses a high risk to individual cryptocurrency users and small-to-medium businesses (SMBs) due to its ability to drain crypto wallets and compromise login credentials. Financial losses from wallet theft can range from hundreds to tens of thousands of dollars per victim. The affected sectors include retail investors, cryptocurrency exchanges, and freelance professionals relying on browser-based wallets. The malware does not encrypt files or demand ransom, but its data exfiltration leads to identity theft and account takeover.

🛡️ Mitigation

Mitigation strategies include deploying endpoint detection and response (EDR) solutions with rules to block execution of svchost.exe from %AppData%, disabling macros in email attachments, and enabling Microsoft Defender for Endpoint’s detections for “AlfonsoStealer” as documented in the Microsoft 365 Defender portal. Organizations should enforce application whitelisting and monitor for unauthorized scheduled tasks named “AlfonsoUpdater” using PowerShell scripts.

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