Russian Hackers Exploit WinRAR Zero-Day to Plant Backdoors in Global Systems

A newly discovered zero-day vulnerability in WinRAR, the popular file compression software with over 500 million users worldwide, is being actively exploited by the Russian state-sponsored hacking group known as RomCom. The critical flaw allows attackers to plant persistent backdoors that give them complete control over compromised systems when users open specially crafted RAR archives.

The vulnerability (CVE-2025-XXXX) exists in WinRAR's processing of recovery volumes, where improper validation of archive headers enables arbitrary code execution. RomCom operators have weaponized this flaw to deploy custom backdoors that establish command-and-control (C2) communications with attacker-controlled servers. Once installed, these backdoors allow full system access, data exfiltration, and lateral movement within networks.

Security researchers tracking RomCom's activities note the group has historically targeted:

• Government agencies
• Defense contractors
• Critical infrastructure operators
• Large corporations

The attack chain begins with spear-phishing emails containing malicious RAR attachments disguised as legitimate documents. When opened in vulnerable WinRAR versions (prior to 6.23), the archive executes embedded malware without user interaction. The backdoor then establishes persistence through registry modifications and scheduled tasks.

Mitigation Recommendations:

1. Immediately update to WinRAR 6.23 or later
2. Block RAR attachments at email gateways
3. Monitor for suspicious child processes from WinRAR.exe
4. Implement application allowlisting
5. Conduct threat hunting for known RomCom IOCs

This incident highlights the continued risk posed by widespread software vulnerabilities being exploited by advanced persistent threat groups. Organizations should prioritize patching and assume breach postures when dealing with such critical flaws.