CVE-2026-39467: MetaSlider Object Injection Vulnerability

CVE-2026-39467 Overview

CVE-2026-39467 is an Insecure Deserialization vulnerability affecting the Responsive Slider by MetaSlider WordPress plugin. The vulnerability allows attackers to perform PHP Object Injection attacks by exploiting improper handling of serialized data within the plugin. This issue affects Responsive Slider by MetaSlider versions through 3.106.0.

Critical Impact

Authenticated attackers with high-level privileges can inject malicious PHP objects, potentially leading to remote code execution, data exfiltration, or complete site compromise depending on available gadget chains in the WordPress environment.

Affected Products

• Responsive Slider by MetaSlider plugin versions through 3.106.0
• WordPress installations using the vulnerable MetaSlider plugin
• Sites with additional plugins that may provide exploitable gadget chains

Discovery Timeline

• 2026-04-21 - CVE CVE-2026-39467 published to NVD
• 2026-04-22 - Last updated in NVD database

Technical Details for CVE-2026-39467

Vulnerability Analysis

This vulnerability stems from CWE-502: Deserialization of Untrusted Data. The MetaSlider Responsive Slider plugin fails to properly validate or sanitize serialized data before processing it through PHP's unserialize() function. When user-controllable data is passed to the deserialization function without adequate security checks, attackers can craft malicious serialized objects that execute arbitrary code upon deserialization.

The attack requires network access and high-level privileges (such as administrator or editor roles) within the WordPress installation. However, once exploited, the impact is severe—affecting confidentiality, integrity, and availability of the compromised system.

Root Cause

The root cause lies in the plugin's improper handling of serialized PHP data. The vulnerable code path accepts user-supplied serialized strings and passes them directly to PHP's native unserialize() function without implementing proper validation, allowlisting of permitted classes, or using safer alternatives like JSON encoding. This design flaw enables PHP Object Injection attacks when combined with available "gadget chains" in the WordPress ecosystem.

Attack Vector

The attack is network-based and requires authenticated access with high privileges. An attacker with administrative or equivalent access to the WordPress dashboard can:

1. Identify input fields or API endpoints that process serialized data in the MetaSlider plugin
2. Craft a malicious serialized PHP object containing dangerous magic methods (__wakeup(), __destruct(), __toString())
3. Submit the payload through the vulnerable functionality
4. Trigger code execution when the plugin deserializes the malicious object

The specific exploitation depends on the presence of "POP chains" (Property-Oriented Programming chains) available in the WordPress core, the MetaSlider plugin itself, or other installed plugins and themes. For detailed technical analysis, refer to the Patchstack WordPress Vulnerability Report.

Detection Methods for CVE-2026-39467

Indicators of Compromise

• Unexpected serialized data patterns containing suspicious class names in POST requests to MetaSlider endpoints
• Web server logs showing unusual unserialize() error messages or PHP object-related warnings
• Presence of unexpected files created in plugin directories or WordPress uploads folder
• Anomalous database entries containing serialized PHP objects with unfamiliar class references

Detection Strategies

• Monitor web application firewall (WAF) logs for serialized PHP object patterns (strings beginning with O:, a:, s: followed by numeric values)
• Implement file integrity monitoring on WordPress plugin directories to detect unauthorized modifications
• Review WordPress admin activity logs for suspicious actions by privileged users
• Deploy endpoint detection solutions to identify post-exploitation activities such as web shells or reverse shell connections

Monitoring Recommendations

• Enable verbose logging for the MetaSlider plugin and monitor for deserialization-related errors
• Configure alerts for unusual HTTP POST request sizes or patterns targeting /wp-admin/ and MetaSlider AJAX endpoints
• Implement real-time monitoring of PHP error logs for object injection indicators
• Use SentinelOne Singularity platform to detect anomalous process execution originating from PHP interpreter processes

How to Mitigate CVE-2026-39467

Immediate Actions Required

• Update the Responsive Slider by MetaSlider plugin to the latest patched version immediately
• Audit all WordPress administrator and editor accounts for suspicious activity or unauthorized access
• Review WordPress user roles and remove unnecessary high-privilege accounts
• Implement Web Application Firewall (WAF) rules to block serialized PHP object patterns in requests

Patch Information

Users should update to a version of the Responsive Slider by MetaSlider plugin newer than 3.106.0 as soon as a patched version becomes available. Monitor the official WordPress plugin repository and the Patchstack security advisory for update notifications. Ensure automatic updates are enabled for WordPress plugins where possible, and always test updates in a staging environment before deploying to production.

Workarounds

• Temporarily deactivate the MetaSlider plugin until a patched version is available if the slider functionality is not business-critical
• Restrict access to the WordPress admin panel using IP allowlisting or VPN requirements
• Implement additional authentication layers (MFA) for all privileged WordPress accounts
• Deploy a WAF rule to block requests containing suspicious serialized PHP patterns targeting MetaSlider endpoints

# WordPress CLI commands for plugin management
# Check current MetaSlider plugin version
wp plugin list --name=ml-slider --fields=name,version,status

# Update MetaSlider plugin to latest version (when patch is available)
wp plugin update ml-slider

# Temporarily deactivate if no patch is available
wp plugin deactivate ml-slider

# Verify plugin status after changes
wp plugin status ml-slider