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Introduction
In 2025, a significant security issue was discovered in Microsoft Windows' Mark of the Web (MOTW) system: CVE-2025-24061. With this protection mechanism failure, attackers can bypass a critical Windows security feature meant to warn users about files downloaded from the internet or other potentially unsafe origins.
Understanding how this works, what the risks are, and how to protect yourself is vital. Below, we break down the issue, show how the exploit works, and give advice for keeping your system safe.
What is Mark of the Web (MOTW)?
Mark of the Web is a special metadata flag Windows automatically adds to files downloaded from the internet. This flag, stored as an "Alternate Data Stream" (ADS) called Zone.Identifier, tells Windows, Office, and browsers to treat the file cautiously. For example:
What Went Wrong? (CVE-2025-24061)
According to Microsoft’s advisory, a protection mechanism failure lets attackers locally bypass MOTW. This means a specially crafted file can *appear innocuous to Windows*, even if it should be flagged by MOTW. Instead of showing warnings or running in restricted modes, Windows runs the file as if it’s trusted.
Remote exploitation is limited unless social engineering is involved.
- This bypass undermines protections in Windows, Microsoft Office, and browsers relying on MOTW to warn or restrict dangerous files.
How Can CVE-2025-24061 be Exploited?
The bug is related to the way Windows applies and reads the Zone.Identifier alternate data stream.
Here’s a step-by-step of how an attacker might use this vulnerability
1. Obtain a Malicious File: The attacker creates a file designed to exploit the target (malicious executable, macro-laced Office file, etc.).
2. Craft the Delivery: Using a flaw in Windows’ handling of the Mark of the Web, attackers either avoid adding the MOTW flag or create a file container (.zip, .iso, etc.) that strips or disables the flag when unpacked.
3. Deliver and Execute: The attacker convinces the victim to extract and run the file. Because the MOTW flag is missing or bypassed, no warning is displayed.
Example Exploit: Bypassing MOTW via Zip Containers
A common exploitation method abuses ZIP files. Windows has a history of not preserving alternate data streams when extracting from archives using certain programs. Some extraction tools and container formats, like .iso or .img, can also strip the MOTW flag during extraction.
You can check if a file has MOTW using PowerShell
Get-Item -Path "malicious.exe" -Stream *
If you don’t see Zone.Identifier in the list, the file doesn’t have MOTW.
You can also read the MOTW contents
Get-Content -Path "malicious.exe:Zone.Identifier"
Typical content for internet-downloaded files
[ZoneTransfer]
ZoneId=3
Here’s a minimalist PoC for demonstration purposes only
# Create a simple file and assign the MOTW
echo "Hello World" > safe.txt
Set-Content -Path "safe.txt:Zone.Identifier" -Value "[ZoneTransfer]`nZoneId=3"
# Verify MOTW exists
Get-Content -Path "safe.txt:Zone.Identifier"
# Pack into a .zip, then extract (simulate user experience)
Compress-Archive -Path safe.txt -DestinationPath test.zip
Expand-Archive -Path test.zip -DestinationPath Extracted
# Check MOTW on extracted file
Get-Item -Path "Extracted\safe.txt" -Stream *
You’ll see that, after extraction, the file often lacks the Zone.Identifier stream—demonstrating the protection loss.
References
- Microsoft CVE-2025-24061 Advisory
- Microsoft: Understanding MOTW
- Alternate Data Streams Explained (Microsoft Docs)
- Security Research: Mark of the Web Bypass with ISOs (.iso)
Use Up-to-date Extraction Tools: Some archive utilities now try to preserve the MOTW.
- Don’t Trust Downloaded Files: Be cautious with ZIP, ISO, and other containers. Even if there are no warnings, the file may be dangerous.
- IT/Admins: Use policies to block or warn about running executables from user-writable directories, like Downloads.
Conclusion
The CVE-2025-24061 vulnerability in Windows’ Mark of the Web shows how attackers can manipulate protections Windows users depend on. While underlying systems like MOTW are crucial for security, flaws and workarounds put users at risk, especially as social engineering becomes more sophisticated.
Stay aware of the risks associated with files and archives, and always keep your system and tools updated for the latest protections.
*This article is for educational purposes only. Do not use this information maliciously. Always practice responsible disclosure and follow local laws and ethical guidelines.*
Timeline
Published on: 03/11/2025 17:16:28 UTC
Last modified on: 04/29/2025 22:06:40 UTC