Zero-Day in Your ZIP: Inside CVE-2025-33028: How a WinZip Flaw Exposes Users to Silent Malware Execution

Introduction: The Silent Power of ZIP Files

In the vast landscape of cybersecurity, it’s often not the zero-click iPhone exploits or flashy ransomware variants that expose the most users — sometimes it’s the tools we’ve trusted for decades. One such example is CVE-2025-33028, a vulnerability in WinZip, a program that’s been a staple in personal and corporate environments for over 30 years.

This blog post explores CVE-2025-33028 — a vulnerability that allows attackers to silently remove Windows security flags (Mark-of-the-Web or MotW) from files during ZIP extraction. We’ll walk through the technical behavior, demonstrate the exploit using real screenshots, and analyze its implications for targeted attacks, including military and espionage operations.

What is CVE-2025-33028?

CVE-2025-33028 is a flaw that impacts how WinZip processes files stamped with Mark-of-the-Web (MotW) — a Windows security feature that stamps files downloaded from the web. When a MotW-stamped file is opened, Windows (or utilities such as Microsoft Office) notifies the user or opens it in Protected View to avoid automatic code execution.

The vulnerability: Extracting a ZIP file containing MotW using exploitable versions of WinZip (such as v21) will not preserve the MotW flag for files within the archive. This enables attackers to insert evil files such as .docm (macro-containing Word documents) into ZIPs that evade Microsoft Office's Protected View.

Affected Software:

Technical Breakdown: How the Exploit Works

Let's do a step-by-step walkthrough in a lab testing environment. Our test used the following:

Step 1: MotW Tagging

When a ZIP file is remotely downloaded from the internet (i.e., downloaded through a web browser), MotW is appended automatically by Windows. This is seen in the file's Properties under Security.

Screenshot 1: test_archive.zip showing “properties showing MotW tag.”

Step 2: Extraction using WinZip

Using vulnerable WinZip version 21.0, we extract the file to a local directory:

C:\Users\vboxuser\Desktop\CVE-2025-33028\extracted_via_winzip

Step 3: Examining Extracted Payload

We now examine the extracted file malicious.docm → Properties.

Screenshot 2: malicious.docm — the “Unblock” checkbox is missing

This demonstrates the crux of the vulnerability: WinZip has removed the MotW. In regular behavior, this file ought to have preserved the MotW flag and cautioned the user when opening it.

Contrastingly, programs such as WinRAR and the Windows native extractor properly preserve the MotW flag on extraction, blocking this type of bypass. This vulnerability makes legitimate-looking ZIP attachments zero-click phishing vectors.

What Makes This Dangerous?

This flaw converts legitimate-looking ZIP attachments into zero-click phishing attacks. After extraction, malicious payloads (such as DOCM, HTA, or JS files) can run without warning — allowing macro execution, script injection, or malware installation.

Threat Actor Usage

If packaged in phishing emails:

Military or Espionage Use Cases

This CVE has nation-state-level potential, particularly in:

Since the user opens the ZIP and clicks the DOCM, security solutions often log it as a legitimate action — making forensic detection harder.

Detection & Mitigation

Detection:

Mitigation:

Conclusion

CVE-2025-33028 isn't a matter of code exploitation — it's a matter of exploiting trust and undernoticed behavior in aged software. When every phishing technique is under observation, this CVE enables attackers to fly under the radar.

By learning and illustrating this weakness, we emphasize the way even old, well-established tools such as WinZip can become avenues for today's attacks — and why technical analysis, as demonstrated above, is vital to blue teams, red teams, and all those in between.

Resources & References

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