Could Your Browser Be Vulnerable to Chihuahua Stealer?

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In 2025, cybersecurity experts are alarmed by a newly detected strain of info stealer called the Chihuahua Stealer. This malware uses advanced techniques that put browser data and cryptocurrency wallet extensions at risk. First flagged by a Reddit user in April of this year, it has since been subjected to detailed analysis, revealing a multitude of sophisticated methods aimed at bypassing conventional security measures. Despite its name, the Chihuahua Stealer employs an unexpectedly advanced arsenal like stealthy loading, scheduled task persistence, and multi-staged payloads designed to make detection exceptionally difficult. Its emergence highlights an escalating challenge in cybersecurity—how to effectively shield consumers and organizations from increasingly complex malware threats. For individuals and companies alike, understanding how this malware operates and what defenses can be implemented is crucial.

Multi-Stage PowerShell Script Infection

The initial form of attack used by the Chihuahua Stealer involves an intricately designed multi-stage PowerShell script, showcasing its complexity and ability to maintain persistence quietly. A major insight from the investigation conducted by G Data CyberDefense found that the malware begins its attack with an obfuscated PowerShell script that users may unknowingly execute, believing it’s a legitimate document. Once activated, the loader triggers a complex multi-staged execution chain employing Base64 encoding and hex-string obfuscation while utilizing scheduled jobs to ensure continued presence. The initial steps involve a lightweight launcher that stealthily executes a Base64-encoded PowerShell string using “iex,” effectively circumventing execution policies. This approach conceals the payload from static analysis and signature-based detection. Then, it progresses to decode and reconstruct a hex payload, dynamically assembling to avoid detection by static and sandbox analyses. The persistence mechanism involves scheduling tasks that scan for infection markers, signaled by “*.normaldaki” files. When markers are detected, subsequent steps involve retrieving additional payloads from command-and-control servers, directed by specific commands. This process culminates in the introduction of a .NET assembly obtained from a remote domain, loading a Base64-obfuscated payload from platforms like OneDrive directly into memory via reflection. This method enables execution while meticulously erasing traces, such as console outputs and clipboard data, minimizing observable indicators of the malware’s presence. Through these intricate mechanisms, the Chihuahua Stealer sets a precedent for modular, adaptive malware capable of persistent data gathering despite efforts to counteract its effects. The complexity and concealment of these operations enable the Chihuahua Stealer to traverse systems quietly, posing a formidable security threat.

Execution, Encryption, and Data Exfiltration

Upon completion of its initial entry, the Chihuahua Stealer initiates its main functions, engaging in a process designed for efficient data extraction and secure exfiltration. A signature step involves executing the DedMaxim() function, during which it displays transliterated Russian rap lyrics on-screen—a signature likely used for identification purposes rather than functionality. However, the subsequent PopilLina() function holds the key operational elements, where the malware interacts with Windows Management Instrumentation (WMI) processes to gather identifying details such as the machine name and disk serial number, which are then obfuscated and hashed to create a unique identifier for the compromised system. This identifier becomes instrumental for naming archives and directories intended to store exfiltrated data. The malware meticulously scans user directories for browser-related files and crypto wallet extension data, employing dynamic path analysis for browsers installed on the user’s system.

Methods for extracting valuable credentials extend to cookies, autofill data, browsing history, sessions, and payment information across detected browsers, as well as targeting crypto wallet extensions by copying pertinent data from folders associated with known wallet extension IDs. After gathering these sensitive data points, the malware processes them for encryption and eventual exfiltration, creating a plaintext file named Brutan.txt for visibility within the working directory. These data are then compressed into a “.chihuahua” archive before encrypting the compiled archive using AES-GCM protocols. The resulting encrypted data file, termed “.VZ”, is subjected to exfiltration attempts toward external servers in a retry-loop format, exploiting headers to mimic a binary file upload. This activity transforms the malware’s presence from local to network-based, posing threats beyond immediate infection scope. Ultimately, data exfiltration operations culminate in the VseLegalno() function, harnessing a WebClient instance to upload the encrypted file to specified external servers, thereby targeting an extended range of vulnerabilities.

Mitigation Recommendations

The Chihuahua Stealer kicks off its attack using a cleverly crafted multi-stage PowerShell script, designed for stealth and persistence. Insights from G Data CyberDefense reveal the malware initiates with an obfuscated PowerShell script that tricks users into executing it, mistaking it for a genuine document. Once running, it triggers a complex execution chain using Base64 encoding and hex-string obfuscation while leveraging scheduled jobs for endurance. The attack starts with a lightweight launcher stealthily running a Base64-encoded PowerShell command through “iex,” sidestepping execution policies. This tactic hides the payload from static analysis and signature detection, decoding a hex payload dynamically to thwart static and sandbox analysis. Persistence involves scheduled tasks that detect infection markers, identified by “*.normaldaki” files. Upon spotting these, further payloads are fetched from command-and-control servers following specific instructions. The climax involves a .NET assembly from a remote domain, loading a Base64-obfuscated payload directly into memory, erasing traces and minimizing the malware’s visible presence. Despite countermeasures, the Chihuahua Stealer remains an adaptable, persistent threat.

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