CVE-2026-6561: EyouCMS Unrestricted Upload RCE Vulnerability

CVE-2026-6561 Overview

A vulnerability has been identified in EyouCMS versions up to 1.7.1 that allows for unrestricted file upload. This issue affects the edit_adminlogo function within the file application/admin/controller/Index.php. By manipulating the filename argument, an attacker can upload arbitrary files to the server. The attack can be executed remotely, and a public exploit is available. The vendor was contacted regarding this disclosure but did not respond.

Critical Impact

Authenticated attackers with high privileges can exploit this unrestricted file upload vulnerability to potentially upload malicious files, leading to sensitive information disclosure or further system compromise.

Affected Products

• EyouCMS versions up to and including 1.7.1
• application/admin/controller/Index.php - edit_adminlogo function

Discovery Timeline

• 2026-04-19 - CVE-2026-6561 published to NVD
• 2026-04-22 - Last updated in NVD database

Technical Details for CVE-2026-6561

Vulnerability Analysis

This vulnerability resides in the edit_adminlogo() function within EyouCMS's administrative controller. The function fails to properly validate or restrict file uploads when processing the filename argument, creating an Unrestricted File Upload condition classified under CWE-284 (Improper Access Control).

The vulnerability requires network access and high privileges (administrative authentication) to exploit, but once those prerequisites are met, no user interaction is required. The impact includes potential confidentiality, integrity, and availability breaches at a limited scope, as attackers could upload malicious files that may lead to sensitive information disclosure or enable further exploitation of the system.

Root Cause

The root cause stems from improper access control and insufficient input validation in the file upload handling mechanism. The edit_adminlogo() function does not adequately verify the type, extension, or content of files being uploaded through the filename parameter, allowing attackers to bypass expected restrictions and upload arbitrary file types.

Attack Vector

The attack is conducted remotely over the network by an authenticated user with administrative privileges. The attacker manipulates the filename argument in requests to the edit_adminlogo function to upload arbitrary files. Since the exploit is publicly available, organizations running vulnerable versions of EyouCMS face increased risk of exploitation.

The vulnerability mechanism involves sending a crafted request to the admin controller's edit_adminlogo endpoint with a manipulated filename parameter. Due to the lack of proper validation, the server accepts and stores arbitrary file content. For detailed technical analysis, refer to the GitHub Vulnerability Notes.

Detection Methods for CVE-2026-6561

Indicators of Compromise

• Unexpected files appearing in administrative upload directories with unusual extensions or names
• HTTP POST requests to /admin/Index/edit_adminlogo containing suspicious filename parameters
• Administrative user accounts performing unusual file upload activities
• Log entries showing requests to the edit_adminlogo endpoint with non-standard file types

Detection Strategies

• Monitor web server access logs for requests targeting the edit_adminlogo endpoint with abnormal filename parameters
• Implement file integrity monitoring on directories where admin logos are stored to detect unauthorized file additions
• Deploy web application firewall (WAF) rules to inspect and block requests with suspicious file upload patterns
• Review audit logs for administrative actions related to logo modification that don't match expected operational patterns

Monitoring Recommendations

• Enable verbose logging on the EyouCMS application to capture detailed request parameters
• Configure alerts for file creation events in the administrative upload directories
• Monitor for execution of unexpected file types within the web application's directory structure
• Implement SentinelOne endpoint protection to detect and alert on suspicious file uploads and potential webshell activity

How to Mitigate CVE-2026-6561

Immediate Actions Required

• Restrict network access to the EyouCMS administrative interface to trusted IP addresses only
• Review and audit all administrative user accounts, removing unnecessary high-privilege access
• Implement additional authentication controls (MFA) for administrative access
• Consider temporarily disabling the edit_adminlogo functionality until a patch is available

Patch Information

As of the last modified date (2026-04-22), no official vendor patch has been released. The vendor was contacted regarding this vulnerability but did not respond. Organizations should monitor the official EyouCMS channels for security updates and consider the workarounds below to reduce exposure.

For additional technical details and tracking information, see VulDB #358198.

Workarounds

• Implement a web application firewall (WAF) rule to filter requests to the edit_adminlogo endpoint with strict filename validation
• Add server-side file type verification at the web server level to restrict uploadable file types
• Disable or remove the edit_adminlogo function if logo customization is not required
• Implement file extension whitelisting at the application or server configuration level

# Example: Restrict access to admin controller in Apache
<Location "/admin/Index/edit_adminlogo">
    Require ip 192.168.1.0/24
    # Deny access from all other IPs
    Require all denied
</Location>