CVE-2025-39503: GoodLayers Hotel Object Injection Flaw

CVE-2025-39503 Overview

CVE-2025-39503 is a critical insecure deserialization vulnerability affecting the GoodLayers Hotel plugin for WordPress. The vulnerability allows attackers to exploit PHP object injection through deserialization of untrusted data, potentially leading to remote code execution, unauthorized data access, or complete site compromise. This issue affects all versions of the Goodlayers Hotel plugin from the initial release through version 3.1.4.

Critical Impact

Unauthenticated attackers can exploit this PHP Object Injection vulnerability to potentially achieve remote code execution, manipulate application data, or escalate privileges on affected WordPress installations.

Affected Products

• GoodLayers Hotel WordPress Plugin versions through 3.1.4
• WordPress installations running vulnerable versions of the gdlr-hotel plugin

Discovery Timeline

• 2025-05-23 - CVE-2025-39503 published to NVD
• 2025-05-23 - Last updated in NVD database

Technical Details for CVE-2025-39503

Vulnerability Analysis

This vulnerability stems from improper handling of serialized data within the GoodLayers Hotel plugin. When the application deserializes user-controlled input without adequate validation, attackers can inject malicious PHP objects into the application's execution flow. The deserialization process can be exploited to instantiate arbitrary objects, invoke magic methods such as __wakeup() or __destruct(), and chain existing classes (commonly known as POP chains) to achieve code execution or other malicious outcomes.

The network-accessible nature of this vulnerability, combined with no authentication requirements, makes it particularly dangerous for public-facing WordPress sites using this plugin.

Root Cause

The root cause is classified under CWE-502 (Deserialization of Untrusted Data). The plugin fails to properly validate or sanitize serialized data before passing it to PHP's unserialize() function. This allows attackers to craft malicious serialized payloads that, when deserialized, can trigger unintended application behavior through PHP's object instantiation and magic method invocation mechanisms.

Attack Vector

The attack is network-based and requires no authentication or user interaction. An attacker can craft a malicious serialized PHP object and submit it to a vulnerable endpoint in the GoodLayers Hotel plugin. When the application deserializes this payload, the attacker-controlled object is instantiated, potentially triggering a chain of method calls that can lead to remote code execution, file manipulation, or database access depending on available gadget chains in the WordPress environment.

The exploitation typically involves:

1. Identifying an entry point that accepts serialized data
2. Crafting a malicious serialized payload using available PHP classes
3. Submitting the payload to the vulnerable endpoint
4. The application deserializes the payload, triggering the attack chain

For detailed technical information, refer to the Patchstack security advisory.

Detection Methods for CVE-2025-39503

Indicators of Compromise

• Unusual PHP error logs referencing unexpected object instantiation or magic method calls
• Web server logs showing requests with base64-encoded or serialized data payloads to plugin endpoints
• New or modified files in WordPress directories, particularly in uploads or plugin folders
• Unexpected database modifications or new administrator accounts
• Outbound network connections from the web server to unknown destinations

Detection Strategies

• Monitor web application logs for requests containing serialized PHP data patterns (strings starting with O:, a:, or s:)
• Implement Web Application Firewall (WAF) rules to detect and block PHP serialization patterns in request parameters
• Deploy file integrity monitoring on WordPress core files, plugins, and themes directories
• Review PHP error logs for deserialization-related warnings or exceptions

Monitoring Recommendations

• Enable verbose logging for the GoodLayers Hotel plugin and WordPress core
• Configure alerts for new user account creation, especially administrator-level accounts
• Monitor for suspicious process execution from web server contexts
• Implement network egress monitoring to detect potential command and control communications

How to Mitigate CVE-2025-39503

Immediate Actions Required

• Update the GoodLayers Hotel plugin to the latest patched version immediately
• If no patch is available, deactivate and remove the gdlr-hotel plugin until a fix is released
• Conduct a security audit of your WordPress installation to identify any signs of compromise
• Review and remove any suspicious administrator accounts or unauthorized file modifications
• Implement a Web Application Firewall with rules to block serialized data injection attempts

Patch Information

Organizations should monitor the official GoodLayers vendor channels and the Patchstack vulnerability database for security updates. Apply patches as soon as they become available from the vendor.

Workarounds

• Temporarily disable the GoodLayers Hotel plugin if business operations permit
• Implement WAF rules to filter and block requests containing PHP serialized object patterns
• Restrict access to WordPress admin and plugin functionality using IP allowlists
• Enable WordPress security plugins that provide runtime application protection against object injection attacks

# Example WAF rule pattern for blocking PHP serialized objects (ModSecurity)
SecRule REQUEST_BODY "@rx O:\d+:\"[a-zA-Z_]" "id:1001,phase:2,deny,status:403,msg:'PHP Object Injection Attempt Blocked'"