CVE-2026-1107: EyouCMS Unrestricted Upload RCE Vulnerability

CVE-2026-1107 Overview

A vulnerability has been identified in EyouCMS up to version 1.7.1/5.0 affecting the Member Avatar Handler component. The weakness exists in the check_userinfo function within the Diyajax.php file, where improper access control allows manipulation of the viewfile argument, leading to unrestricted file upload capabilities. This vulnerability can be exploited remotely by authenticated attackers, potentially resulting in arbitrary code execution through file inclusion.

Critical Impact

Remote attackers with low privileges can exploit improper access control in the Member Avatar Handler to upload arbitrary files, potentially leading to code execution on affected EyouCMS installations.

Affected Products

• EyouCMS versions up to 1.7.1
• EyouCMS versions up to 5.0
• Systems running the vulnerable Diyajax.php Member Avatar Handler component

Discovery Timeline

• 2026-01-18 - CVE-2026-1107 published to NVD
• 2026-01-18 - Last updated in NVD database

Technical Details for CVE-2026-1107

Vulnerability Analysis

This vulnerability stems from improper access control (CWE-284) in EyouCMS's Member Avatar Handler functionality. The check_userinfo function in Diyajax.php fails to properly validate and restrict file operations when processing the viewfile parameter. This improper access control weakness enables attackers to bypass intended restrictions on file uploads, creating a pathway to execute arbitrary code on the server.

The vulnerability is accessible over the network and requires only low-level authentication privileges to exploit. Once exploited, an attacker can achieve limited impacts on confidentiality, integrity, and availability of the affected system. The exploit code has been publicly disclosed, increasing the risk of active exploitation in the wild. Notably, the vendor was contacted about this disclosure but did not respond.

Root Cause

The root cause of this vulnerability is improper access control in the check_userinfo function. The function fails to adequately validate the viewfile argument before processing file operations, allowing attackers to manipulate this parameter to upload files without proper authorization checks. This represents a fundamental failure in input validation and access control mechanisms within the Member Avatar Handler component.

Attack Vector

The attack vector is network-based, allowing remote exploitation. An authenticated attacker with minimal privileges can send crafted requests to the Diyajax.php endpoint, manipulating the viewfile parameter to upload malicious files. The attack flow typically involves:

1. Authenticating to the EyouCMS application with a low-privileged account
2. Sending a crafted request to the Member Avatar Handler endpoint
3. Manipulating the viewfile parameter to bypass upload restrictions
4. Uploading a malicious file (such as a PHP webshell)
5. Accessing the uploaded file to achieve code execution

For technical details and proof-of-concept code, refer to the GitHub PoC Repository and VulDB #341699.

Detection Methods for CVE-2026-1107

Indicators of Compromise

• Unexpected file uploads in avatar or media directories, particularly PHP files or other executable content
• Anomalous HTTP requests to Diyajax.php containing suspicious viewfile parameter values
• Web server access logs showing unusual patterns targeting the Member Avatar Handler endpoint
• New or modified files with suspicious extensions in upload directories

Detection Strategies

• Monitor HTTP traffic for requests to Diyajax.php with manipulated viewfile parameters
• Implement file integrity monitoring on upload directories to detect unauthorized file additions
• Configure web application firewalls (WAF) to detect and block file inclusion attack patterns
• Review web server access logs for repeated requests to the vulnerable endpoint from suspicious sources

Monitoring Recommendations

• Enable detailed logging for the EyouCMS application, particularly for file upload operations
• Set up alerts for file creation events in upload directories, especially for executable file types
• Monitor for outbound connections from web servers that may indicate successful compromise
• Implement runtime application self-protection (RASP) to detect exploitation attempts

How to Mitigate CVE-2026-1107

Immediate Actions Required

• Restrict access to the Diyajax.php endpoint through web server configuration until a patch is available
• Implement strict file type validation for all upload functionality
• Review and remove any suspicious files from upload directories
• Consider temporarily disabling the Member Avatar Handler functionality if not critical

Patch Information

At the time of publication, no official patch has been released by the vendor. The vendor was contacted about this disclosure but did not respond. Organizations should monitor the official EyouCMS channels for security updates. In the absence of an official patch, implementing the workarounds below is strongly recommended. Additional information is available at VulDB #341699 Details.

Workarounds

• Implement web server rules to block requests containing suspicious viewfile parameter patterns
• Add server-side file type validation to restrict uploads to safe file formats (images only)
• Configure upload directories with non-executable permissions to prevent code execution
• Deploy a web application firewall (WAF) with rules to detect file inclusion attacks

# Apache configuration to restrict access to vulnerable endpoint
# Add to .htaccess or Apache configuration file

<Files "Diyajax.php">
    # Restrict access to trusted IP addresses only
    Require ip 192.168.1.0/24
    # Alternatively, deny all external access
    # Require all denied
</Files>

# Disable PHP execution in upload directories
<Directory "/path/to/eyoucms/uploads">
    php_admin_flag engine off
    AddHandler default-handler .php .phtml .php3 .php4 .php5
</Directory>