CVE-2025-69906: Monstra CMS File Upload RCE Vulnerability

CVE-2025-69906 Overview

CVE-2025-69906 is an arbitrary file upload vulnerability affecting Monstra CMS version 3.0.4. The vulnerability exists in the Files Manager plugin, which relies on a blacklist-based file extension validation mechanism to filter uploaded files. This insecure approach allows attackers to bypass the validation and upload files with extensions that can be interpreted as executable code by the web server, ultimately leading to remote code execution (RCE).

The application stores uploaded files directly in a web-accessible directory, making it trivial for an attacker to access and execute malicious payloads after successful upload. Under typical server configurations running PHP, an attacker can upload a malicious PHP file that executes arbitrary commands on the underlying system.

Critical Impact
Successful exploitation allows unauthenticated or low-privileged attackers to achieve remote code execution on the web server, potentially leading to full system compromise, data theft, and lateral movement within the network.

Affected Products

Monstra CMS v3.0.4
Monstra CMS Files Manager Plugin

Discovery Timeline

2026-02-05 - CVE-2025-69906 published to NVD
2026-02-05 - Last updated in NVD database

Technical Details for CVE-2025-69906

Vulnerability Analysis

This arbitrary file upload vulnerability stems from an insecure file validation approach in the Monstra CMS Files Manager plugin. The application uses blacklist-based validation to determine which file extensions are prohibited from upload, rather than implementing a secure whitelist approach that only permits known-safe file types.

Blacklist-based validation is inherently flawed because it requires anticipating every possible malicious file extension, including variations and alternative extensions that web servers may interpret as executable. Attackers can often bypass such restrictions using techniques like double extensions (e.g., file.php.png), alternative PHP extensions (e.g., .phtml, .php5, .phar), or case manipulation depending on server configuration.

Once a malicious file is uploaded, it is stored in a web-accessible directory without additional security controls. This means the attacker can directly request the uploaded file via HTTP, causing the web server to execute the embedded malicious code with the privileges of the web server process.

Root Cause

The root cause of CVE-2025-69906 is the reliance on blacklist-based file extension validation in the Files Manager plugin. This approach fails to account for all potentially dangerous file types and alternative extensions that may be interpreted as executable by the web server. Additionally, the lack of content-type verification, file content inspection, and storage isolation contributes to the exploitability of this vulnerability.

Secure file upload implementations should use whitelist validation that only permits explicitly approved file types, verify file content matches declared type, rename uploaded files to remove executable extensions, and store files outside the web root or in a location where execution is disabled.

Attack Vector

The attack vector for this vulnerability involves an authenticated user with access to the Files Manager plugin uploading a malicious file that bypasses the blacklist validation. The attack flow typically follows these steps:

The attacker authenticates to the Monstra CMS administrative panel or gains access to the Files Manager functionality
The attacker crafts a malicious file with an extension that bypasses the blacklist (e.g., using alternative PHP extensions or double extensions)
The file is uploaded through the Files Manager interface
The application stores the file in a web-accessible directory
The attacker navigates to the uploaded file's URL, triggering execution of the malicious payload
The web server executes the payload, granting the attacker remote code execution capabilities

For detailed technical information and proof-of-concept details, refer to the GitHub PoC repository for CVE-2025-69906.

Detection Methods for CVE-2025-69906

Indicators of Compromise

Unusual files with PHP-executable extensions appearing in the Monstra CMS upload directories (e.g., files ending in .phtml, .php5, .phar, or double extensions like .php.jpg)
Web server logs showing HTTP requests to unexpected PHP files in upload directories
Newly created files in web-accessible directories with recent timestamps that don't correspond to legitimate administrative activity
Web shell signatures or known malicious PHP patterns in uploaded files

Detection Strategies

Implement file integrity monitoring on Monstra CMS upload directories to detect unauthorized file creation
Configure web application firewall (WAF) rules to inspect file upload requests and block suspicious file types
Deploy endpoint detection and response (EDR) solutions capable of detecting web shell activity and anomalous process spawning from web server processes
Enable detailed logging for file upload operations and monitor for failed validation bypass attempts

Monitoring Recommendations

Monitor web server access logs for requests to executable files in upload directories that should only contain static content
Set up alerts for PHP process spawning unusual child processes such as cmd.exe, sh, bash, or powershell
Implement real-time file system monitoring on web server upload directories with alerts for newly created executable files
Review authentication logs for the Monstra CMS admin panel to identify unauthorized access attempts

How to Mitigate CVE-2025-69906

Immediate Actions Required

Restrict access to the Monstra CMS administrative panel and Files Manager to trusted IP addresses only
Audit existing uploaded files in web-accessible directories for suspicious or unexpected file types
Configure the web server to disable PHP execution in upload directories using .htaccess or server configuration directives
Consider temporarily disabling the Files Manager plugin until a patch is available or the application is upgraded

Patch Information

At the time of publication, no official patch information is available from the Monstra CMS maintainers. Organizations using Monstra CMS v3.0.4 should monitor the official Monstra CMS GitHub repository for security updates and consider migrating to an actively maintained CMS platform.

Workarounds

Configure Apache or Nginx to disable script execution in upload directories by adding appropriate directives (e.g., php_flag engine off in .htaccess for Apache)
Implement a web application firewall (WAF) with rules to block file uploads containing executable content or suspicious extensions
Store uploaded files outside the web root and serve them through a dedicated script that enforces content-type headers and prevents execution
Restrict Files Manager access to only trusted administrative users and implement additional authentication factors

bash

# Apache .htaccess configuration to disable PHP execution in uploads directory
# Place this file in the Monstra CMS uploads directory
# /public/uploads/.htaccess

php_flag engine off
RemoveHandler .php .phtml .php3 .php4 .php5 .phar
AddType text/plain .php .phtml .php3 .php4 .php5 .phar