CVE-2026-19116 in User Frontend Plugin
Summary
by MITRE • 09/02/2026
The User Frontend WordPress plugin before 4.3.11 does not prevent user-supplied field values from being deserialized when a submitted post is reopened in its frontend editing form, allowing authenticated users with subscriber-level access and above to perform PHP Object Injection, which may lead to remote code execution when a suitable gadget chain is present on the site.
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Analysis
by VulDB Data Team • 09/02/2026
The vulnerability identified in the User Frontend WordPress plugin prior to version 4.3.11 represents a critical security flaw rooted in improper handling of serialized data within the application's frontend editing workflow. Specifically, the plugin fails to validate or sanitize user-supplied field values when a previously submitted post is reopened for editing through its frontend interface. This architectural oversight allows an attacker who has authenticated access at the subscriber level or higher to inject maliciously crafted PHP objects into the system. The core technical failure lies in the direct deserialization of untrusted input, which bypasses standard security controls that should restrict such operations to trusted internal data structures only.
From a technical perspective, this flaw is classified under CWE-502, which denotes Deserialization of Untrusted Data. When an authenticated user submits or modifies content via the frontend form, the plugin processes these inputs and stores them in a serialized format. Upon reopening the post for editing, the application retrieves this data and passes it directly to PHP's unserialize function without adequate verification of its integrity or origin. This behavior creates a vector for PHP Object Injection, where an attacker can manipulate the serialized payload to instantiate arbitrary classes with controlled properties. If the target WordPress installation includes third-party plugins or themes that contain vulnerable gadget chains, these injected objects can trigger unintended side effects during their instantiation methods, such as __wakeup or destructors.
The operational impact of this vulnerability is severe, potentially leading to Remote Code Execution (RCE) on the affected server. An attacker leveraging a suitable gadget chain can execute arbitrary PHP code with the privileges of the web server process. This compromise allows for full control over the WordPress environment, including the ability to read sensitive files, modify database contents, install backdoors, or pivot further into the internal network. The requirement for authenticated access at even the lowest privilege level (subscriber) significantly lowers the barrier to entry for attackers, as many users obtain such credentials through simple registration processes on public-facing sites that allow user contributions.
This vulnerability aligns with MITRE ATT&CK technique T1059, specifically Command and Scripting Interpreter sub-techniques related to PHP execution, as well as T1203, which covers Exploitation for Client Execution if the attack vector targets client-side components, though in this context it primarily facilitates server-side exploitation. The lack of input validation during deserialization is a common pattern in legacy or poorly maintained plugins that prioritize convenience over security.
To mitigate this risk, administrators should immediately update the User Frontend plugin to version 4.3.11 or later, where the developers have implemented proper sanitization and validation checks before processing user inputs for serialization. In cases where updating is not immediately feasible, it is advisable to restrict frontend editing capabilities to users with higher privilege levels such as editors or administrators, thereby reducing the attack surface available to low-privilege accounts. Additionally, implementing a Web Application Firewall (WAF) rule that detects and blocks common PHP object injection patterns in POST requests can provide an additional layer of defense against exploitation attempts while patching efforts are underway. Regular security audits focusing on deserialization practices across all installed plugins are also recommended to prevent similar vulnerabilities from being introduced or exploited in the future.