Critical Zero-Day Vulnerability in WinRAR Sparks Active Exploitation

A significant security flaw has been discovered in WinRAR, the popular file compression tool used worldwide. This high-severity zero-day vulnerability has been actively exploited by two Russian cybercrime groups over the past few weeks. The attackers utilize malicious archives attached to phishing emails—some of which are highly personalized—to compromise targeted systems.

How the Attacks Are Carried Out

Security company ESET first identified suspicious activity on July 18, when their telemetry detected a file located in an unusual directory path. By July 24, analysts confirmed that this behavior was linked to the exploitation of an unknown vulnerability within WinRAR. Given that WinRAR is installed on approximately 500 million devices globally, the potential impact of this flaw is considerable.

Upon discovery, ESET promptly notified the WinRAR development team. The company responded swiftly, releasing a security patch within six days to address the vulnerability and prevent further exploitation.

Technical Details of the Exploit

The exploit demonstrated a sophisticated use of Windows features, notably the manipulation of alternate data streams—a Windows capability that allows multiple data streams to be associated with a single file. Attackers leveraged this feature to trigger a previously unknown path traversal vulnerability.

This flaw enabled the malicious code to be planted in critical system directories such as %TEMP% and %LOCALAPPDATA%. These directories are typically protected from such activity because they are designated for temporary and user-specific data, respectively, and are usually restricted from executing code directly.

The exploitation of this flaw allowed the attackers to execute malicious executables remotely, effectively turning WinRAR into a vector for malware deployment.

Implications and Recommendations

The discovery of this zero-day highlights the importance of timely security updates and vigilance when handling unsolicited or suspicious email attachments. Users of WinRAR are strongly advised to update their software to the latest version to mitigate the risk of infection from these ongoing attacks.

Organizations should also monitor for signs of compromise and reinforce email security protocols to prevent phishing campaigns from infiltrating their networks.

Ethan Cole

I'm Ethan Cole, a tech journalist with a passion for uncovering the stories behind innovation. I write about emerging technologies, startups, and the digital trends shaping our future. Read me on x.com