CVE-2026-14558 Overview
CVE-2026-14558 is a PHP Object Injection vulnerability in the User Frontend WordPress plugin versions prior to 4.3.10. The plugin fails to validate field type definitions and deserializes user-controlled post metadata when rendering submitted posts. Authenticated users with Editor-level access or higher can inject arbitrary PHP objects into the deserialization flow. When a suitable Property-Oriented Programming (POP) chain exists on the target site, this object injection can escalate to remote code execution. The flaw is categorized under CWE-502: Deserialization of Untrusted Data.
Critical Impact
Editor-level attackers can inject arbitrary PHP objects through unvalidated post metadata, enabling remote code execution when a compatible POP gadget chain is present.
Affected Products
- User Frontend WordPress plugin versions before 4.3.10
- WordPress sites with Editor-level or higher user accounts using the plugin
- WordPress installations where the plugin renders submitted post metadata
Discovery Timeline
- 2026-08-28 - CVE-2026-14558 published to NVD
- 2026-08-28 - Last updated in NVD database
Technical Details for CVE-2026-14558
Vulnerability Analysis
The User Frontend plugin accepts post metadata submitted by authenticated users and passes it through PHP's deserialization routines when rendering posts. Because the plugin does not enforce field type definitions before unserializing values, an attacker can supply crafted serialized data in place of expected scalar metadata. PHP then instantiates arbitrary objects based on the attacker-controlled payload, invoking magic methods such as __wakeup, __destruct, or __toString during object lifecycle events. When classes loaded on the site expose exploitable behavior in these magic methods, the injection chain can be pivoted into filesystem writes, command execution, or arbitrary PHP evaluation.
Root Cause
The root cause is unsafe use of unserialize() on user-controlled post metadata combined with missing validation of declared field types. The plugin trusts metadata values submitted through frontend forms and does not restrict the data to expected primitive types before passing it to deserialization. This design permits any Editor-level actor to smuggle serialized object payloads through legitimate submission workflows.
Attack Vector
Exploitation requires an authenticated account with Editor privileges or higher. The attacker submits a post through the User Frontend plugin containing serialized PHP object data in a metadata field. When the plugin later renders the post, PHP deserializes the payload and constructs the attacker-specified objects. Successful remote code execution depends on the presence of a usable POP chain among the installed themes, plugins, or WordPress core classes on the target site. Refer to the WPScan Vulnerability Report for further technical detail.
Detection Methods for CVE-2026-14558
Indicators of Compromise
- Post metadata entries containing PHP serialized object markers such as O: followed by a class name and length prefix.
- Unexpected file writes, cron entries, or PHP files appearing under the wp-content directory after post submissions.
- Outbound network connections initiated by the PHP-FPM or web server process shortly after Editor-level submissions.
- Web server logs showing Editor accounts submitting posts with unusually large or binary metadata payloads.
Detection Strategies
- Inspect wp_postmeta rows for serialized object signatures rather than expected scalar values in fields managed by the User Frontend plugin.
- Enable WordPress audit logging to correlate Editor-level post submissions with subsequent errors or PHP warnings referencing unserialize.
- Monitor for anomalous process execution from the PHP interpreter such as spawning shells, curl, or wget.
Monitoring Recommendations
- Alert on the WordPress plugin version reported by asset inventories when it is below 4.3.10.
- Track privileged WordPress role assignments and flag new Editor or Administrator accounts.
- Forward web server and PHP error logs to a central SIEM for correlation against post submission events.
How to Mitigate CVE-2026-14558
Immediate Actions Required
- Update the User Frontend plugin to version 4.3.10 or later on every affected WordPress site.
- Audit existing Editor and higher role accounts and remove any that are unused or unrecognized.
- Review wp_postmeta for serialized object payloads and remove malicious entries before restoring service.
Patch Information
The vendor has released User Frontend version 4.3.10, which addresses the improper validation of field type definitions and removes the unsafe deserialization of user-controlled post metadata. Site operators should apply this update through the WordPress plugin manager or by deploying the updated plugin package. Details are referenced in the WPScan Vulnerability Report.
Workarounds
- Temporarily restrict Editor-level access to trusted users only until the patch is applied.
- Disable the User Frontend plugin on sites that cannot immediately upgrade to version 4.3.10.
- Place a web application firewall rule in front of the site that inspects post submission bodies for PHP serialized object patterns.
Disclaimer: This content was generated using AI. While we strive for accuracy, please verify critical information with official sources.
