WinRAR, the trusted file compression tool used by millions globally, has once again become the target of a critical remote code execution (RCE) vulnerability, and this one could be devastating for businesses and individuals alike.

If your organization regularly deals with compressed files, contracts, invoices, or client documents, you could unknowingly be exposing your systems to hackers. Here's what you need to know to stay safe.

What Happened?

Think of WinRAR as your digital filing cabinet. For years, it's helped users easily compress and extract files. But recent cybersecurity reports flag a high-severity flaw that could flip this useful tool into a hacker’s gateway.

Discovered by researcher whs3-detonator and reported via the Zero Day Initiative on June 5, 2025, the flaw is a directory traversal vulnerability. In simple terms, hackers can use it to sneak malicious files into critical Windows folders, such as the Startup directory, just by tricking someone into opening a specially crafted .rar archive.

Once the infected file is extracted, code execution can occur on the next reboot.

Real-World Damage: How Bad Can It Get?

• July 2025: A small business in New York lost $15,000 in downtime after a phishing email led an employee to extract a malicious archive. The payload? Ransomware that stole sensitive client data.

• 2024: A Chicago-based company took a $200,000 hit when an outdated WinRAR version was exploited to deliver Remcos RAT (Remote Access Trojan), giving hackers remote access to the firm’s network.

• 2023: Hackers used a separate WinRAR flaw to embed malware in fake PDF files, targeting crypto traders and causing $500,000 in losses, according to Uptycs.

Clearly, this isn't WinRAR’s first rodeo, and unless users take action, it won’t be the last.

Why Do These Attacks Keep Happening?

The issue lies in WinRAR’s complex file parsing mechanisms, especially for .rar and recovery volumes. Here's where it fails:

• Weak validation of file paths

• Inadequate input sanitization

• Overlooked edge cases in how archives are handled

These gaps allow attackers to craft seemingly normal archive files that execute malicious code, install malware, or create persistent backdoors into a system.

And in many cases, it all starts with a simple phishing email. In June 2025, attackers targeted law firms with fake invoice attachments, infecting several with malware via this exact exploit.

Three Key Takeaways & Action Steps

At CyberStreams, we’re passionate about keeping your digital environment secure. Here’s what we recommend:

1. Update WinRAR Immediately

Upgrade to WinRAR 7.12 beta 1 or later, which patches the latest vulnerability. Not sure how? Our managed services can automate patching for you.

2. Scan Archives Before Opening

Always scan .rar files from unknown sources using a reliable antivirus. Our EDR & SOC services offer real-time threat detection to help stop threats before they spread.

3. Use Alternative Archivers

Consider switching to 7-Zip. It’s free, open source, and has a better track record for security vulnerabilities.

Conclusion: Don’t Wait; Patch or Pay

Cybercriminals are banking on the fact that most users don’t update their software. With over 500 million WinRAR users worldwide (per RARLAB), even a small percentage using outdated versions creates a massive attack surface.

This latest vulnerability is a wake-up call. Whether you're a solo freelancer or a growing enterprise, keeping software updated is non-negotiable in today's threat landscape.

Don't let a simple .rar file become your organization's worst nightmare. Patch now, scan often, and stay vigilant.