CVE-2025-0767: WP Activity Log Insecure Deserialization

CVE-2025-0767 Overview

A critical insecure deserialization vulnerability has been identified in WP Activity Log version 5.3.2, a popular WordPress plugin used for security auditing and activity monitoring. The vulnerability exists in the class-csv-writer.php file where unvalidated user input is passed directly to PHP's unserialize() function, potentially allowing attackers to execute arbitrary code or manipulate application behavior.

Critical Impact

Attackers can exploit this insecure deserialization flaw to potentially inject malicious objects, leading to remote code execution, data manipulation, or denial of service on affected WordPress installations.

Affected Products

• Melapress WP Activity Log version 5.3.2
• WordPress sites running vulnerable WP Activity Log plugin installations

Discovery Timeline

• 2025-02-27 - CVE-2025-0767 published to NVD
• 2025-05-21 - Last updated in NVD database

Technical Details for CVE-2025-0767

Vulnerability Analysis

This vulnerability falls under CWE-502 (Deserialization of Untrusted Data), a severe class of vulnerabilities that occurs when applications deserialize data from untrusted sources without proper validation. In PHP applications, the unserialize() function can instantiate arbitrary objects and trigger magic methods like __wakeup() or __destruct(), which attackers can chain together to achieve code execution through Property Oriented Programming (POP) chains.

The vulnerability requires network access to exploit but has high attack complexity due to the need for a suitable gadget chain to be present in the application's codebase or loaded plugins. Successful exploitation could result in integrity and availability impacts on the affected WordPress installation.

Root Cause

The root cause of this vulnerability lies in the improper handling of user-supplied data within the myapp/classes/Writers/class-csv-writer.php file. The application passes user-controlled input directly to the unserialize() function without implementing proper input validation, sanitization, or using safer alternatives like json_decode(). This architectural flaw violates secure coding principles that dictate untrusted data should never be deserialized without strict type checking and allowlisting.

Attack Vector

The attack vector is network-based, requiring an attacker to craft malicious serialized PHP objects and submit them to the vulnerable endpoint. The exploitation process involves:

1. Identifying the vulnerable parameter that accepts serialized data
2. Analyzing the WordPress installation and loaded plugins for exploitable PHP classes (gadget chains)
3. Crafting a malicious serialized payload that chains together methods to achieve the desired outcome
4. Submitting the payload to trigger the unserialize() call and execute the attack chain

The vulnerability resides in the CSV export functionality of the WP Activity Log plugin. Attackers can craft malicious serialized objects targeting available PHP classes in the WordPress ecosystem. When the unserialize() function processes this malicious input in the class-csv-writer.php file, it can instantiate attacker-controlled objects and trigger dangerous magic methods. For detailed technical analysis, refer to the Fluid Attacks Security Advisory.

Detection Methods for CVE-2025-0767

Indicators of Compromise

• Unusual HTTP requests containing serialized PHP objects (look for patterns like O: followed by class names) targeting WP Activity Log endpoints
• Unexpected PHP errors or exceptions related to object instantiation in server logs
• Anomalous file system activity or process spawning following requests to CSV export functionality
• Web application firewall logs showing blocked serialization-related payloads

Detection Strategies

• Deploy web application firewall (WAF) rules to detect and block serialized PHP object patterns in request parameters
• Monitor WordPress error logs for deserialization-related exceptions or warnings from the WP Activity Log plugin
• Implement application-level logging to track all calls to the CSV writer functionality
• Use file integrity monitoring to detect unauthorized changes to WordPress core files or plugins

Monitoring Recommendations

• Enable verbose logging for the WP Activity Log plugin and review logs for suspicious activity patterns
• Configure alerting for HTTP requests containing serialized data patterns targeting /wp-admin/ and plugin-specific endpoints
• Monitor for unusual outbound network connections from the web server that could indicate successful exploitation
• Regularly audit installed WordPress plugins for known vulnerabilities using security scanning tools

How to Mitigate CVE-2025-0767

Immediate Actions Required

• Update WP Activity Log to the latest patched version immediately
• Review server logs for any indicators of exploitation attempts
• Temporarily disable the WP Activity Log plugin if an update is not immediately available
• Implement WAF rules to block serialized PHP object payloads targeting WordPress endpoints

Patch Information

Organizations should update to the latest version of WP Activity Log that addresses this insecure deserialization vulnerability. Check the WordPress Plugin Directory for the latest available version and update instructions. Review the Fluid Attacks Security Advisory for additional remediation guidance.

Workarounds

• Restrict access to WordPress admin functionality to trusted IP addresses using .htaccess or server-level firewall rules
• Deploy a web application firewall configured to block common PHP deserialization attack patterns
• Disable or remove the WP Activity Log plugin temporarily until a patched version can be applied
• Implement application-level input validation to sanitize or reject serialized data in request parameters

# Apache .htaccess rule to restrict wp-admin access
<IfModule mod_rewrite.c>
RewriteEngine On
RewriteCond %{REQUEST_URI} ^/wp-admin [NC]
RewriteCond %{REMOTE_ADDR} !^192\.168\.1\.100$
RewriteRule .* - [F,L]
</IfModule>