CVE-2026-54194 Overview
CVE-2026-54194 is a PHP Object Injection vulnerability in the Fusion Builder plugin for WordPress affecting versions up to and including 3.15.4. The flaw stems from insecure deserialization of untrusted input [CWE-502] processed by the plugin. An authenticated attacker with Contributor-level privileges can inject crafted serialized PHP objects into the application. When these objects deserialize, attacker-controlled magic methods can trigger property-oriented programming chains. Successful exploitation can lead to remote code execution, data tampering, or full site compromise depending on available gadget chains in the WordPress installation.
Critical Impact
A Contributor-level account can trigger PHP object injection in Fusion Builder ≤ 3.15.4, enabling code execution and full WordPress site compromise.
Affected Products
- Fusion Builder plugin for WordPress, versions ≤ 3.15.4
- WordPress sites permitting Contributor-level registration with Fusion Builder installed
- Avada theme deployments bundling vulnerable Fusion Builder releases
Discovery Timeline
- 2026-06-17 - CVE-2026-54194 published to NVD
- 2026-06-17 - Last updated in NVD database
Technical Details for CVE-2026-54194
Vulnerability Analysis
The vulnerability is classified as Insecure Deserialization under [CWE-502]. Fusion Builder ≤ 3.15.4 passes attacker-controlled input to PHP's unserialize() function without validating the serialized payload. PHP deserialization rebuilds object graphs from a string and automatically invokes lifecycle methods such as __wakeup(), __destruct(), and __toString(). When these magic methods exist on classes present in the WordPress runtime or other loaded plugins, an attacker can chain them into a property-oriented programming (POP) gadget that performs file writes, command execution, or arbitrary SQL queries. The Contributor role normally allows only draft post creation, yet here it provides sufficient access to reach the vulnerable sink.
Root Cause
The root cause is the use of unserialize() on data sourced from a request handler accessible to low-privilege authenticated users. Fusion Builder does not constrain accepted classes, does not apply the allowed_classes option, and does not validate input format before deserialization.
Attack Vector
An attacker registers or compromises a Contributor account, then submits a crafted request to a Fusion Builder endpoint containing a serialized PHP payload. The payload references gadget classes from WordPress core or co-installed plugins to achieve a desired side effect during deserialization. No user interaction is required beyond the attacker's own authenticated request.
No public proof-of-concept code is available. Refer to the Patchstack Vulnerability Report for additional technical detail.
Detection Methods for CVE-2026-54194
Indicators of Compromise
- POST requests from Contributor accounts containing serialized PHP markers such as O:, a:, or s: in body parameters targeting Fusion Builder AJAX actions.
- Unexpected PHP files created under wp-content/uploads/ or modifications to theme and plugin PHP files following Contributor activity.
- New administrator accounts or modified user roles created shortly after Contributor post submissions.
- Outbound network connections from the web server process to unfamiliar hosts after Fusion Builder requests.
Detection Strategies
- Inspect web server and WordPress audit logs for serialized PHP patterns in request parameters bound for Fusion Builder endpoints.
- Correlate Contributor-level authentication events with subsequent file system writes inside WordPress directories.
- Enable a Web Application Firewall ruleset that flags unserialize() payload signatures and PHP object notation in HTTP requests.
Monitoring Recommendations
- Forward WordPress and PHP-FPM logs to a central data lake and alert on serialized object patterns reaching Fusion Builder routes.
- Monitor for new or modified PHP files under WordPress installation directories using file integrity monitoring.
- Track privilege changes within wp_users and wp_usermeta for accounts that recently submitted draft content.
How to Mitigate CVE-2026-54194
Immediate Actions Required
- Update Fusion Builder to a version newer than 3.15.4 once released by the vendor and validated against the Patchstack advisory.
- Audit all WordPress accounts and remove or downgrade unused Contributor, Author, and Editor accounts.
- Disable open user registration if not required for site operation.
- Place WordPress behind a Web Application Firewall configured to block PHP object injection patterns.
Patch Information
Consult the Patchstack Vulnerability Report for the fixed release information and vendor remediation guidance. Apply the vendor-supplied update to all sites running Fusion Builder ≤ 3.15.4.
Workarounds
- Restrict Contributor registration and require administrator approval for new accounts until the patch is applied.
- Deploy WAF rules that drop requests containing PHP serialization tokens to Fusion Builder AJAX endpoints.
- Limit write permissions on the web root so the PHP process cannot create or modify executable files.
# Example WAF rule snippet (ModSecurity) blocking serialized PHP payloads to Fusion Builder
SecRule REQUEST_URI "@contains /wp-admin/admin-ajax.php" \
"chain,phase:2,deny,status:403,id:1026054194,msg:'Possible PHP Object Injection in Fusion Builder'"
SecRule ARGS "@rx O:\d+:\"[A-Za-z_\\\\]+\":\d+:\{" "t:none"
Disclaimer: This content was generated using AI. While we strive for accuracy, please verify critical information with official sources.
