CVE-2026-24378: EventPrime Object Injection Vulnerability

CVE-2026-24378 Overview

A critical deserialization of untrusted data vulnerability has been identified in the Metagauss EventPrime plugin for WordPress (eventprime-event-calendar-management). This vulnerability allows attackers to perform PHP Object Injection attacks against vulnerable WordPress installations. Successful exploitation can lead to complete site compromise, including remote code execution, data theft, and total system takeover.

Critical Impact

This PHP Object Injection vulnerability allows unauthenticated attackers to inject arbitrary PHP objects, potentially leading to remote code execution, complete site compromise, and data exfiltration on WordPress sites running vulnerable versions of EventPrime.

Affected Products

• EventPrime (eventprime-event-calendar-management) versions through 4.2.8.0
• WordPress installations using vulnerable EventPrime plugin versions
• All sites with EventPrime plugin versions from n/a through <= 4.2.8.0

Discovery Timeline

• 2026-03-25 - CVE-2026-24378 published to NVD
• 2026-03-26 - Last updated in NVD database

Technical Details for CVE-2026-24378

Vulnerability Analysis

This vulnerability is classified as CWE-502 (Deserialization of Untrusted Data), which occurs when an application deserializes data from an untrusted source without properly validating its contents. In the context of the EventPrime WordPress plugin, the application processes serialized PHP data that can be manipulated by attackers to inject malicious objects.

PHP Object Injection vulnerabilities are particularly dangerous in WordPress environments due to the extensive class inheritance and magic methods available across WordPress core, themes, and plugins. When a vulnerable unserialize() function processes attacker-controlled data, it can instantiate arbitrary classes and trigger their magic methods such as __destruct(), __wakeup(), or __toString(), leading to a variety of malicious outcomes.

The network-accessible nature of this vulnerability combined with no required authentication makes it especially concerning for internet-facing WordPress installations. Attackers can exploit this vulnerability remotely without any prior access to the target system.

Root Cause

The root cause of this vulnerability lies in the improper handling of serialized data within the EventPrime plugin. The application accepts serialized PHP data from user-controllable input sources and passes it to the unserialize() function without adequate validation or sanitization. This allows attackers to craft malicious serialized payloads that, when deserialized, instantiate arbitrary PHP objects with attacker-controlled properties.

Attack Vector

The attack vector for this vulnerability is network-based, requiring no authentication or user interaction. An attacker can exploit this vulnerability by sending specially crafted HTTP requests containing malicious serialized PHP payloads to vulnerable WordPress sites. The exploitation chain typically involves:

1. Identifying a vulnerable EventPrime installation
2. Crafting a malicious serialized PHP object payload
3. Identifying available "gadget chains" within WordPress core, plugins, or themes that can be abused during deserialization
4. Sending the payload to the vulnerable endpoint
5. Triggering remote code execution or other malicious actions through the gadget chain

The vulnerability can be exploited to achieve remote code execution if suitable gadget chains exist in the WordPress environment. Additional information is available in the Patchstack security advisory.

Detection Methods for CVE-2026-24378

Indicators of Compromise

• Unusual HTTP POST requests to EventPrime plugin endpoints containing serialized PHP data patterns (e.g., O:, a:, s: prefixes)
• Web server logs showing requests with base64-encoded or URL-encoded serialized PHP objects
• Unexpected file modifications in WordPress directories, particularly in wp-content/uploads/ or plugin folders
• Creation of new administrator accounts or modification of existing user privileges
• Suspicious outbound network connections from the web server

Detection Strategies

• Deploy web application firewall (WAF) rules to detect and block serialized PHP object patterns in HTTP requests
• Implement file integrity monitoring on WordPress core files, plugins, and themes directories
• Monitor web server access logs for requests containing PHP serialization markers targeting EventPrime endpoints
• Use WordPress security plugins to scan for known indicators of object injection exploitation
• Enable PHP error logging and monitor for deserialization-related warnings or errors

Monitoring Recommendations

• Configure real-time alerting for requests matching PHP serialization patterns in WAF or SIEM systems
• Implement automated vulnerability scanning to identify unpatched EventPrime installations across your environment
• Monitor WordPress user tables for unauthorized account creation or privilege escalation
• Set up network traffic analysis to detect command and control communications from compromised servers
• Regularly audit installed plugin versions against known vulnerability databases

How to Mitigate CVE-2026-24378

Immediate Actions Required

• Update the EventPrime plugin to a patched version immediately (versions above 4.2.8.0)
• If immediate patching is not possible, temporarily deactivate the EventPrime plugin until a fix can be applied
• Review web server logs for evidence of exploitation attempts targeting the EventPrime plugin
• Conduct a security audit of WordPress installations to identify any indicators of compromise
• Consider implementing a Web Application Firewall with rules to block PHP object injection attempts

Patch Information

Site administrators should update the EventPrime Event Calendar Management plugin to the latest available version that addresses this vulnerability. The patch should be available through the WordPress plugin repository. For detailed patch information and verification, consult the Patchstack vulnerability database entry.

Workarounds

• Temporarily disable the EventPrime plugin if updates cannot be immediately applied
• Implement WAF rules to filter requests containing serialized PHP object patterns targeting EventPrime endpoints
• Restrict access to WordPress admin and plugin endpoints through IP whitelisting where feasible
• Enable PHP's disable_functions directive to block dangerous functions that could be leveraged in gadget chains
• Consider using a virtual patching solution to protect against exploitation while awaiting the official patch

# Example WAF rule concept for blocking PHP object injection patterns
# Add to .htaccess or web server configuration as appropriate
# This is a conceptual example - adapt to your specific WAF/server

# Block requests with common PHP serialization patterns
# ModSecurity rule example:
# SecRule REQUEST_BODY "@rx O:\d+:\"[^\"]+\":\d+:{" "id:100001,phase:2,deny,status:403,msg:'PHP Object Injection Attempt'"