CVE-2025-12673: Flex QR Code Generator RCE Vulnerability

CVE-2025-12673 Overview

The Flex QR Code Generator plugin for WordPress contains a critical arbitrary file upload vulnerability due to missing file type validation in the update_qr_code() function. This flaw affects all versions up to and including 1.2.6, allowing unauthenticated attackers to upload arbitrary files to the affected site's server, potentially enabling remote code execution.

Critical Impact

Unauthenticated attackers can upload malicious files including PHP web shells to achieve remote code execution on vulnerable WordPress installations.

Affected Products

• Flex QR Code Generator WordPress Plugin versions ≤ 1.2.6
• WordPress installations running vulnerable plugin versions

Discovery Timeline

• December 6, 2025 - CVE-2025-12673 published to NVD
• December 8, 2025 - Last updated in NVD database

Technical Details for CVE-2025-12673

Vulnerability Analysis

This vulnerability is classified as CWE-434 (Unrestricted Upload of File with Dangerous Type). The update_qr_code() function in the Flex QR Code Generator plugin fails to properly validate file types before allowing uploads to the server. This fundamental security control oversight enables attackers to bypass intended restrictions and upload executable files, including PHP scripts that can serve as web shells or backdoors.

The vulnerability is particularly dangerous because it does not require authentication. Any remote attacker with network access to the WordPress installation can exploit this flaw without needing valid credentials, significantly lowering the barrier to compromise.

Root Cause

The root cause of this vulnerability lies in the absence of file type validation within the update_qr_code() function located in qr-code-generator.php. The function accepts file uploads without verifying that the uploaded content matches allowed file types such as image formats. Without this validation, the application cannot distinguish between legitimate QR code image uploads and malicious executable files.

Attack Vector

The attack vector is network-based and requires no user interaction or authentication. An attacker can craft a malicious HTTP request to the vulnerable endpoint, submitting a file with a dangerous extension (such as .php) that contains executable code. Once uploaded, the attacker can access the uploaded file directly through the web server, triggering execution of the malicious payload.

The exploitation process involves identifying a vulnerable WordPress installation with the Flex QR Code Generator plugin, crafting a specially formatted request to the update_qr_code() endpoint with a malicious PHP file, and then accessing the uploaded file to execute arbitrary commands on the server.

For technical details on the vulnerable code path, refer to the WordPress Plugin Code Review and the Ryan Kozak Security Post.

Detection Methods for CVE-2025-12673

Indicators of Compromise

• Unexpected PHP files in WordPress upload directories, particularly in plugin-related folders
• Web server access logs showing POST requests to QR code generator endpoints with unusual file extensions
• Presence of web shell files or backdoors in the WordPress installation
• Unauthorized outbound connections from the web server to suspicious IP addresses

Detection Strategies

• Monitor file system changes in WordPress plugin directories for newly created executable files
• Implement web application firewall (WAF) rules to detect file upload attempts with dangerous extensions
• Review web server logs for suspicious POST requests targeting the Flex QR Code Generator plugin endpoints
• Use file integrity monitoring tools to alert on unexpected files in the WordPress installation

Monitoring Recommendations

• Enable detailed logging on the WordPress installation to capture all file upload activities
• Configure intrusion detection systems to alert on PHP file creation in upload directories
• Implement real-time monitoring of web server access logs for exploitation attempts
• Periodically scan WordPress installations for known web shell signatures

How to Mitigate CVE-2025-12673

Immediate Actions Required

• Update the Flex QR Code Generator plugin to a patched version immediately if available
• Disable or remove the Flex QR Code Generator plugin until a patch is applied
• Audit the WordPress installation for any unauthorized files that may have been uploaded
• Review server access logs for signs of exploitation attempts

Patch Information

Users should monitor the Wordfence Vulnerability Report for the latest patch availability information. The plugin should be updated to a version newer than 1.2.6 once a security fix is released by the developer.

Workarounds

• Temporarily disable the Flex QR Code Generator plugin until a patched version is available
• Implement server-side file upload restrictions to block dangerous file extensions at the web server level
• Use a web application firewall (WAF) to filter malicious file upload attempts
• Restrict access to the WordPress admin and plugin functionality to trusted IP addresses only

# Apache .htaccess configuration to block PHP execution in uploads directory
<Directory "/var/www/html/wp-content/uploads">
    <FilesMatch "\.php$">
        Require all denied
    </FilesMatch>
</Directory>