CVE-2025-39500: Goodlayers Hostel Deserialization Flaw

CVE-2025-39500 Overview

CVE-2025-39500 is a critical deserialization of untrusted data vulnerability affecting the GoodLayers Hostel WordPress plugin. This vulnerability enables attackers to perform PHP Object Injection attacks, which can lead to arbitrary code execution, data manipulation, or complete site compromise. The flaw exists in versions up to and including 3.1.2 of the plugin.

Critical Impact

Unauthenticated attackers can exploit this PHP Object Injection vulnerability to execute arbitrary code, manipulate database contents, or gain complete control over affected WordPress installations.

Affected Products

• GoodLayers Hostel WordPress Plugin versions through 3.1.2
• WordPress installations using the vulnerable plugin
• Websites utilizing GoodLayers Hostel for booking and reservation functionality

Discovery Timeline

• 2025-05-23 - CVE-2025-39500 published to NVD
• 2025-05-23 - Last updated in NVD database

Technical Details for CVE-2025-39500

Vulnerability Analysis

This vulnerability stems from improper handling of serialized data within the GoodLayers Hostel plugin. When the application deserializes user-supplied input without proper validation, it allows attackers to inject malicious PHP objects into the application's execution flow. The attack requires no authentication and can be executed remotely over the network, making it particularly dangerous for internet-facing WordPress sites.

PHP Object Injection vulnerabilities occur when user-controlled input is passed to PHP's unserialize() function without adequate sanitization. If the application contains classes with exploitable magic methods (such as __wakeup(), __destruct(), or __toString()), attackers can chain these methods to achieve arbitrary code execution or other malicious outcomes.

Root Cause

The root cause of CVE-2025-39500 is the insecure deserialization of untrusted data (CWE-502). The GoodLayers Hostel plugin fails to properly validate or sanitize serialized data before processing it, allowing attackers to craft malicious serialized objects that execute arbitrary code when deserialized by the vulnerable application.

Attack Vector

The vulnerability is exploitable via network-based attacks without requiring any user interaction or prior authentication. An attacker can craft a malicious serialized PHP object and submit it to a vulnerable endpoint within the GoodLayers Hostel plugin. Upon deserialization, the malicious object triggers a chain of method calls (known as a "POP chain" - Property Oriented Programming) that can lead to remote code execution.

The attack typically involves:

1. Identifying a vulnerable deserialization point in the plugin
2. Discovering usable gadget classes within WordPress core or installed plugins
3. Constructing a malicious serialized payload that chains these gadgets
4. Sending the payload to the vulnerable endpoint to trigger code execution

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

Detection Methods for CVE-2025-39500

Indicators of Compromise

• Unexpected PHP serialized data in HTTP request parameters or POST bodies
• Unusual process spawning from PHP or web server processes
• Suspicious file creation or modification in WordPress directories
• Anomalous outbound network connections from the web server
• Unauthorized administrator account creation or privilege changes

Detection Strategies

• Monitor web server access logs for requests containing serialized PHP objects (look for patterns like O: followed by class names)
• Implement Web Application Firewall (WAF) rules to detect and block serialized object payloads
• Review PHP error logs for deserialization-related errors or unexpected class instantiation
• Deploy file integrity monitoring to detect unauthorized modifications to WordPress files

Monitoring Recommendations

• Enable verbose logging for the WordPress application and web server
• Configure alerting for suspicious HTTP requests targeting plugin endpoints
• Monitor system processes for unusual child processes spawned by web server workers
• Implement network traffic analysis to detect command and control communications

How to Mitigate CVE-2025-39500

Immediate Actions Required

• Update the GoodLayers Hostel plugin to a patched version immediately if one is available
• If no patch is available, consider temporarily disabling the plugin until a fix is released
• Implement WAF rules to block serialized PHP object payloads at the network perimeter
• Review WordPress user accounts for any unauthorized additions or privilege escalations
• Conduct a thorough security audit of the affected WordPress installation

Patch Information

Check the Patchstack Vulnerability Report for the latest patch availability and update instructions. Organizations should prioritize updating to a version newer than 3.1.2 once a security patch is released by GoodLayers.

Workarounds

• Temporarily disable the GoodLayers Hostel plugin if it is not critical to site operations
• Implement strict input validation and WAF rules to filter serialized data in requests
• Restrict access to WordPress admin areas using IP whitelisting
• Consider using a WordPress security plugin that provides virtual patching capabilities
• Monitor the vendor's official channels for security update announcements

If the plugin must remain active, ensure comprehensive logging and monitoring are in place to detect potential exploitation attempts. Network-level controls such as a WAF configured with PHP serialization detection rules can provide an additional layer of defense while awaiting an official patch.