CVE-2025-39485: Grand Tour WordPress Object Injection Flaw

CVE-2025-39485 Overview

CVE-2025-39485 is a critical Insecure Deserialization vulnerability affecting the ThemeGoods Grand Tour | Travel Agency WordPress theme. The vulnerability allows unauthenticated attackers to perform PHP Object Injection attacks by exploiting improper handling of serialized data within the theme. This class of vulnerability can lead to severe consequences including remote code execution, file manipulation, and complete site compromise when combined with suitable gadget chains present in the WordPress installation.

Critical Impact

Unauthenticated attackers can inject malicious PHP objects, potentially leading to remote code execution, data exfiltration, or complete WordPress site takeover.

Affected Products

• ThemeGoods Grand Tour | Travel Agency WordPress theme versions up to and including 5.5.1
• All WordPress installations running the vulnerable Grand Tour theme versions
• Sites using the Grand Tour theme with additional plugins containing exploitable gadget chains

Discovery Timeline

• 2025-05-23 - CVE CVE-2025-39485 published to NVD
• 2026-01-28 - Last updated in NVD database

Technical Details for CVE-2025-39485

Vulnerability Analysis

This vulnerability stems from the theme's failure to properly validate and sanitize serialized data before passing it to PHP's unserialize() function. When user-controlled input is deserialized without adequate validation, attackers can craft malicious serialized payloads that instantiate arbitrary PHP objects with attacker-controlled properties.

The attack requires no authentication and can be performed remotely over the network. The exploitation does not require any user interaction, making it particularly dangerous for internet-facing WordPress installations. Upon successful exploitation, attackers can achieve high impact to confidentiality, integrity, and availability of the affected system.

Root Cause

The root cause is classified under CWE-502 (Deserialization of Untrusted Data). The Grand Tour theme processes serialized PHP data from untrusted sources without implementing proper security controls. This occurs when the application accepts serialized user input and passes it directly to unserialize() without:

1. Validating the source of the serialized data
2. Implementing allowlist-based class restrictions
3. Using safer alternatives like JSON encoding/decoding
4. Sanitizing or filtering the serialized content before processing

Attack Vector

The attack vector is network-based, requiring no privileges or user interaction. Attackers can exploit this vulnerability by sending specially crafted HTTP requests containing malicious serialized PHP payloads to the vulnerable WordPress installation.

The exploitation technique involves crafting a serialized PHP object that, when deserialized, triggers dangerous operations through magic methods such as __wakeup(), __destruct(), or __toString(). The actual impact depends on the availability of "gadget chains" - sequences of classes that can be chained together to achieve code execution or other malicious outcomes.

Common exploitation scenarios include:

• Leveraging existing WordPress core or plugin classes as gadget chains
• Chaining multiple object instantiations to achieve file write capabilities
• Exploiting autoloading mechanisms to include malicious code

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

Detection Methods for CVE-2025-39485

Indicators of Compromise

• Unusual HTTP POST requests containing serialized PHP data (strings starting with O: or a: followed by numeric values)
• Web server logs showing requests with base64-encoded serialized payloads
• Unexpected file creation or modification in the WordPress installation directory
• New or modified PHP files containing malicious code in theme or upload directories
• Unauthorized WordPress user accounts or privilege escalations

Detection Strategies

• Deploy Web Application Firewall (WAF) rules to detect and block serialized PHP data in request parameters
• Monitor web server access logs for suspicious POST requests targeting theme-related endpoints
• Implement file integrity monitoring on WordPress core, theme, and plugin directories
• Configure intrusion detection systems to alert on PHP object injection patterns

Monitoring Recommendations

• Enable detailed logging for all HTTP requests to the WordPress installation
• Set up alerts for any new file creation or modification in the wp-content/themes/grandtour/ directory
• Monitor for outbound network connections from the web server that could indicate successful exploitation
• Regularly audit WordPress user accounts for unauthorized additions or privilege changes

How to Mitigate CVE-2025-39485

Immediate Actions Required

• Update the Grand Tour | Travel Agency WordPress theme to a version newer than 5.5.1 that contains the security patch
• If an update is not immediately available, consider temporarily disabling the theme and switching to a default WordPress theme
• Implement Web Application Firewall rules to block serialized PHP data in user input
• Review server logs for any signs of exploitation attempts or successful compromise

Patch Information

Site administrators should check for updates to the Grand Tour theme through the WordPress theme update mechanism or directly from ThemeGoods. The vulnerability affects all versions from the initial release through version 5.5.1. Consult the Patchstack vulnerability database for the latest patch status and remediation guidance.

Workarounds

• Deploy a Web Application Firewall with rules specifically designed to detect and block PHP object injection attempts
• Use security plugins such as Wordfence or Sucuri that can provide virtual patching capabilities
• Restrict access to the WordPress admin and theme-related endpoints using IP allowlisting where possible
• Implement Content Security Policy headers to limit the impact of potential code execution

# Example Apache .htaccess rule to block common serialized PHP patterns
# Add to your WordPress root .htaccess file
<IfModule mod_rewrite.c>
    RewriteEngine On
    RewriteCond %{QUERY_STRING} (O:[0-9]+:|a:[0-9]+:{) [NC,OR]
    RewriteCond %{REQUEST_BODY} (O:[0-9]+:|a:[0-9]+:{) [NC]
    RewriteRule .* - [F,L]
</IfModule>