CVE-2025-31396: FLAP WordPress Theme Object Injection Flaw

CVE-2025-31396 Overview

A critical Deserialization of Untrusted Data vulnerability has been identified in the FLAP - Business WordPress Theme developed by themeton. This vulnerability allows attackers to perform PHP Object Injection attacks against affected WordPress installations. The flaw stems from improper handling of serialized data, enabling unauthenticated attackers to inject malicious PHP objects that could lead to complete site compromise.

Critical Impact

Unauthenticated attackers can exploit this PHP Object Injection vulnerability to potentially achieve remote code execution, manipulate data, or gain unauthorized access to the WordPress installation without any user interaction required.

Affected Products

• FLAP - Business WordPress Theme versions up to and including 1.5
• WordPress installations using the vulnerable FLAP theme
• Websites with themeton FLAP theme activated

Discovery Timeline

• 2025-06-09 - CVE CVE-2025-31396 published to NVD
• 2025-06-12 - Last updated in NVD database

Technical Details for CVE-2025-31396

Vulnerability Analysis

This vulnerability is classified under CWE-502 (Deserialization of Untrusted Data), a well-documented weakness category that occurs when applications deserialize data from untrusted sources without adequate validation. In the context of the FLAP WordPress theme, the vulnerability allows for PHP Object Injection, which is particularly dangerous in WordPress environments due to the rich ecosystem of classes available for exploitation through gadget chains.

The attack can be executed remotely over the network without requiring any authentication or user interaction. When successfully exploited, attackers can achieve high-impact outcomes affecting the confidentiality, integrity, and availability of the target system. This could include reading sensitive configuration data, modifying database contents, or disrupting site operations entirely.

Root Cause

The root cause of CVE-2025-31396 lies in the FLAP theme's failure to properly validate and sanitize serialized data before passing it to PHP's unserialize() function. WordPress themes that accept user-controlled serialized input without verification create opportunities for attackers to craft malicious payloads containing specially constructed PHP objects. When these objects are instantiated during deserialization, their magic methods (such as __wakeup(), __destruct(), or __toString()) can be exploited to execute arbitrary code or perform other malicious operations.

Attack Vector

The attack is network-based, requiring no privileges or user interaction. Attackers can craft malicious serialized PHP objects and submit them through theme-related input vectors such as theme options, shortcode attributes, or AJAX handlers. The exploitability depends on the presence of "gadget" classes within the WordPress installation that contain exploitable magic methods.

When the vulnerable theme deserializes the attacker-controlled input, the injected objects are instantiated. If suitable POP (Property-Oriented Programming) chains exist within WordPress core, installed plugins, or the theme itself, attackers can chain multiple gadget classes together to achieve arbitrary file operations, SQL injection, or remote code execution.

Detection Methods for CVE-2025-31396

Indicators of Compromise

• Unusual serialized data patterns in web server access logs containing base64-encoded or URL-encoded serialized PHP objects
• Unexpected outbound network connections from the web server indicating potential reverse shell activity
• Modified WordPress theme files, particularly within the /wp-content/themes/flap/ directory
• Suspicious database entries containing serialized object data with unexpected class references
• Web application firewall logs showing attempts to inject PHP serialized payloads

Detection Strategies

• Implement Web Application Firewall (WAF) rules to detect and block PHP serialized object patterns in incoming requests
• Monitor WordPress file integrity using security plugins to detect unauthorized modifications
• Review web server access logs for requests containing suspicious serialized data patterns such as O: or a: prefixes
• Deploy endpoint detection solutions to identify post-exploitation behavior on web servers

Monitoring Recommendations

• Enable verbose logging on WordPress installations and review logs for deserialization-related errors
• Configure real-time alerting for new file creation or modification within theme directories
• Monitor for unusual PHP process behavior including unexpected child processes or network connections
• Implement database query monitoring to detect anomalous INSERT or UPDATE operations targeting options tables

How to Mitigate CVE-2025-31396

Immediate Actions Required

• Deactivate and remove the FLAP - Business WordPress Theme immediately if no patch is available
• Implement Web Application Firewall rules to block serialized PHP object injection attempts
• Review WordPress installation for signs of compromise and restore from clean backups if necessary
• Audit all installed themes and plugins for similar deserialization vulnerabilities
• Consider temporarily switching to a default WordPress theme until a patched version of FLAP is released

Patch Information

As of the last NVD update on 2025-06-12, users should consult the Patchstack vulnerability database for the latest patch information and remediation guidance from themeton. Monitor the theme developer's official channels for security updates addressing this vulnerability.

Workarounds

• Replace any usage of unserialize() with json_decode() for handling user input if custom code modifications are feasible
• Implement input validation filters at the server level to reject requests containing serialized PHP object patterns
• Use WordPress security plugins that provide virtual patching capabilities for known vulnerabilities
• Restrict theme file permissions to prevent unauthorized modifications using appropriate file system permissions

# Configuration example - File permission hardening for WordPress themes
# Navigate to your WordPress installation directory
cd /var/www/html/wp-content/themes

# Set restrictive permissions on theme files
find . -type f -exec chmod 644 {} \;
find . -type d -exec chmod 755 {} \;

# Ensure proper ownership
chown -R www-data:www-data flap/

# Optional: Make theme files immutable (requires root)
# chattr +i flap/functions.php