EUVD-2026-5649: Critical Vulnerability Analysis

WP Duplicate Plugin - Authentication Bypass to Remote Code Execution

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1. VULNERABILITY ASSESSMENT AND SEVERITY EVALUATION

Severity Classification

CVSS 3.1 Base Score: 9.8 (CRITICAL)

The vulnerability receives the maximum severity rating across multiple dimensions:

• Attack Vector (AV:N): Network-exploitable, requiring no physical or local access
• Attack Complexity (AC:L): Low complexity, easily reproducible
• Privileges Required (PR:N): No authentication required for final exploitation
• User Interaction (UI:N): No user interaction needed
• Scope (S:U): Unchanged scope
• Impact Triad (C:H/I:H/A:H): Complete compromise of confidentiality, integrity, and availability

Technical Assessment

This is a two-stage vulnerability chain that escalates from an authenticated low-privilege attack to complete unauthenticated remote code execution:

1. Stage 1: Missing authorization check (CWE-862) on process_add_site() AJAX action
2. Stage 2: Path traversal combined with arbitrary file upload leading to RCE

The vulnerability is particularly severe because:

• Initial exploitation requires only subscriber-level access (lowest authenticated privilege)
• Once the prod_key_random_id option is set, unauthenticated attackers can exploit the system
• Direct path to remote code execution through arbitrary file upload
• No user interaction required for exploitation

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2. POTENTIAL ATTACK VECTORS AND EXPLOITATION METHODS

Attack Chain Analysis

Phase 1: Initial Foothold (Authenticated - Subscriber Level)

Attacker Action: Exploit process_add_site() AJAX endpoint
Target: /wp-admin/admin-ajax.php
Method: POST
Required Privilege: Subscriber (authenticated)
Objective: Set prod_key_random_id option value

Exploitation Steps:

1. Attacker creates a subscriber-level account (often possible through public registration)
2. Sends crafted AJAX request to process_add_site() without capability checks
3. Sets internal prod_key_random_id option to attacker-controlled value
4. This value acts as an authentication bypass token

Phase 2: Unauthenticated Remote Code Execution

Attacker Action: Upload malicious file via handle_upload_single_big_file()
Target: File upload endpoint
Method: POST with prod_key_random_id
Required Privilege: None (unauthenticated)
Objective: Write PHP webshell to server

Exploitation Steps:

1. Attacker uses previously set prod_key_random_id to bypass authentication
2. Exploits path traversal vulnerability in file upload functionality
3. Uploads malicious PHP file (webshell) to web-accessible directory
4. Executes arbitrary code by accessing uploaded file via HTTP request

Proof of Concept Attack Flow

1. POST /wp-admin/admin-ajax.php
   action=process_add_site
   [Set prod_key_random_id to known value]
   [Authenticated as subscriber]

2. POST /wp-admin/admin-ajax.php (or similar endpoint)
   action=handle_upload_single_big_file
   prod_key_random_id=[known value from step 1]
   file=../../wp-content/uploads/shell.php
   [Unauthenticated request]

3. GET /wp-content/uploads/shell.php?cmd=whoami
   [Remote code execution achieved]

Attack Vectors

• Direct exploitation: Attackers with subscriber accounts
• Credential stuffing: Using compromised credentials from data breaches
• Social engineering: Tricking site administrators into creating accounts
• Automated scanning: Mass exploitation via vulnerability scanners
• Supply chain attacks: Compromising sites to pivot to connected systems

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3. AFFECTED SYSTEMS AND SOFTWARE VERSIONS

Affected Product

• Plugin Name: WP Duplicate (also referenced as "Local Sync" in code repositories)
• Vendor: Revmakx
• Affected Versions: All versions up to and including 1.1.8
• Platform: WordPress CMS

Vulnerable Code Locations

Based on the provided references:

1. Authorization Bypass:

   • admin/class-local-sync-admin.php (Line 422)
   • Function: process_add_site()

2. File Upload Handler:

   • includes/class-local-sync-handle-server-requests.php (Line 389)
   • Function: Authentication check bypass

3. Path Traversal:

   • admin/class-local-sync-files-op.php (Line 843)
   • Function: handle_upload_single_big_file()

Deployment Scope

• WordPress installations with WP Duplicate plugin versions ≤ 1.1.8
• Estimated exposure: Potentially thousands of WordPress sites
• Geographic distribution: Global, with significant European presence

System Requirements for Exploitation

• Target must have WP Duplicate plugin installed and activated
• WordPress site must allow user registration (for initial foothold) OR attacker has existing subscriber-level credentials
• Web server must have write permissions to exploitable directories

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4. RECOMMENDED MITIGATION STRATEGIES

Immediate Actions (Priority 1 - Within 24 Hours)

For Site Administrators:

1. Disable or Remove Plugin

   # Via WP-CLI
   wp plugin deactivate local-sync
   wp plugin delete local-sync
   

   • Immediately deactivate WP Duplicate plugin
   • Remove plugin entirely if not critical to operations

2. Emergency Patching

   • Update to version 1.1.9 or later (if available)
   • Monitor vendor security advisories for patch release

3. Access Control Hardening

   // Temporary .htaccess rule to block AJAX actions
   <Files "admin-ajax.php">
       Order Allow,Deny
       Deny from all
       Allow from [trusted IP ranges]
   </Files>
   

4. Audit User Accounts

   • Review all subscriber-level accounts created in past 90 days
   • Disable user registration if not required
   • Implement CAPTCHA on registration forms

For Security Teams:

5. Incident Response Procedures

   • Search web server logs for suspicious AJAX requests:

   grep "process_add_site" /var/log/apache2/access.log
   grep "handle_upload_single_big_file" /var/log/apache2/access.log
   

6. File Integrity Monitoring

   • Scan for unauthorized PHP files:

   find /var/www/html/wp-content/uploads -name "*.php" -type f -mtime -30
   

7. Database Inspection

   SELECT * FROM wp_options WHERE option_name = 'prod_key_random_id';
   

   • Check if prod_key_random_id has been set
   • Remove suspicious option values

Short-Term Mitigations (Priority 2 - Within 1 Week)

8. Web Application Firewall (WAF) Rules

   # ModSecurity rule example
   SecRule ARGS:action "@streq process_add_site" \
       "id:1000001,phase:2,deny,status:403,\
       msg:'WP Duplicate vulnerability block'"
   
   SecRule ARGS:action "@streq handle_upload_single_big_file" \
       "id:1000002,phase:2,deny,status:403,\
       msg:'WP Duplicate file upload block'"
   

9. Network Segmentation

   • Isolate WordPress installations from critical infrastructure
   • Implement egress filtering to prevent reverse shells

10. Enhanced Monitoring

    • Deploy SIEM rules for detecting exploitation attempts
    • Monitor for unusual file uploads and modifications
    • Alert on new PHP files in upload directories

Long-Term Security Measures (Priority 3 - Ongoing)

11. Security Hardening