CVE-2025-31631: Fish House Object Injection Vulnerability

CVE-2025-31631 Overview

CVE-2025-31631 is a critical Insecure Deserialization vulnerability affecting the AncoraThemes Fish House WordPress theme. The vulnerability allows attackers to perform PHP Object Injection attacks by exploiting improper handling of serialized data. This issue affects Fish House theme versions from the initial release through 1.2.7.

Critical Impact

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

Affected Products

• AncoraThemes Fish House WordPress Theme versions up to and including 1.2.7
• WordPress installations using vulnerable Fish House theme versions
• Websites with Fish House theme installed regardless of activation status

Discovery Timeline

• 2025-05-23 - CVE-2025-31631 published to NVD
• 2025-05-23 - Last updated in NVD database

Technical Details for CVE-2025-31631

Vulnerability Analysis

This vulnerability falls under CWE-502 (Deserialization of Untrusted Data), which occurs when an application deserializes data from an untrusted source without proper validation. In the context of the Fish House WordPress theme, the application processes serialized PHP objects from user-controlled input without adequate security controls.

PHP Object Injection vulnerabilities are particularly dangerous in WordPress environments due to the extensive use of magic methods (__wakeup(), __destruct(), __toString()) across the WordPress core, themes, and plugins. When a malicious serialized object is unserialized, these magic methods can be chained together in a "POP chain" (Property Oriented Programming) to achieve arbitrary code execution or other malicious outcomes.

The network-accessible nature of this vulnerability means attackers can exploit it remotely without requiring any authentication or user interaction, significantly increasing the risk to affected installations.

Root Cause

The root cause of this vulnerability is the improper handling of serialized data within the Fish House theme. The theme processes user-supplied serialized input using PHP's unserialize() function without implementing proper validation, sanitization, or type restrictions. This allows attackers to craft malicious serialized objects that, when deserialized, can trigger dangerous operations through PHP's magic methods.

WordPress themes and plugins that use unserialize() on user-controllable data create a significant attack surface, especially when combined with gadget chains available in the WordPress ecosystem.

Attack Vector

The attack is network-based and can be executed by unauthenticated remote attackers. An attacker would craft a malicious serialized PHP object containing carefully constructed property values designed to exploit existing class methods (gadgets) within the WordPress environment.

The exploitation process typically involves:

1. Identifying an entry point where serialized data is accepted by the Fish House theme
2. Analyzing available classes for exploitable magic methods that can be chained
3. Constructing a malicious serialized payload targeting these gadget chains
4. Submitting the payload to the vulnerable endpoint
5. Upon deserialization, the malicious object triggers the chain of methods leading to code execution or other malicious outcomes

For detailed technical information about this vulnerability, refer to the Patchstack WordPress Vulnerability Report.

Detection Methods for CVE-2025-31631

Indicators of Compromise

• Unusual serialized data patterns in web server access logs, particularly containing PHP class names or magic method references
• Unexpected file modifications within the WordPress installation directory
• Suspicious outbound network connections originating from the web server
• Creation of unauthorized administrator accounts or user privilege changes
• Presence of webshells or backdoor files in theme directories

Detection Strategies

• Implement Web Application Firewall (WAF) rules to detect and block serialized PHP object patterns in HTTP requests
• Monitor PHP error logs for deserialization-related warnings or exceptions
• Deploy file integrity monitoring to detect unauthorized changes to WordPress core, theme, and plugin files
• Analyze HTTP request payloads for common PHP serialization signatures such as O:, a:, s: patterns

Monitoring Recommendations

• Enable detailed logging for all HTTP POST requests to WordPress installations
• Configure alerts for unusual process spawning from PHP-FPM or Apache/Nginx worker processes
• Implement real-time monitoring of WordPress theme directory for file changes
• Review authentication logs for any unexpected administrative access attempts

How to Mitigate CVE-2025-31631

Immediate Actions Required

• Update the Fish House WordPress theme to a patched version immediately if available from AncoraThemes
• If no patch is available, consider temporarily deactivating and removing the vulnerable theme
• Implement WAF rules to block requests containing serialized PHP object patterns
• Conduct a security audit of your WordPress installation for signs of compromise
• Review and restrict file system permissions for the WordPress installation

Patch Information

Organizations should check with AncoraThemes for an updated version of the Fish House theme that addresses this PHP Object Injection vulnerability. Monitor the Patchstack WordPress Vulnerability Report for updates on patch availability and additional remediation guidance.

Workarounds

• Deploy a Web Application Firewall with rules specifically designed to detect PHP serialization attacks
• Implement server-side input validation to reject any requests containing serialized PHP data
• Use security plugins that provide object injection protection for WordPress installations
• Consider switching to an alternative theme until a security patch is released

# Example WAF rule pattern for ModSecurity to detect PHP serialization
SecRule REQUEST_BODY "@rx (O|a|s):\d+:" \
    "id:9001,\
    phase:2,\
    deny,\
    status:403,\
    msg:'Potential PHP Object Injection detected',\
    severity:'CRITICAL'"