CVE-2026-19116: User Frontend WordPress Plugin RCE Vulnerability

CVE-2026-19116 Overview

CVE-2026-19116 is a PHP Object Injection vulnerability in the User Frontend WordPress plugin before version 4.3.11. The plugin fails to prevent deserialization of user-supplied field values when a submitted post is reopened in its frontend editing form. Authenticated attackers with subscriber-level access or above can inject arbitrary PHP objects into the application. When a suitable gadget chain exists on the target site, this can escalate to remote code execution. The flaw is tracked under CWE-502: Deserialization of Untrusted Data.

Critical Impact
Authenticated subscribers can trigger PHP Object Injection that may lead to remote code execution on vulnerable WordPress sites.

Affected Products

User Frontend WordPress plugin versions prior to 4.3.11
WordPress installations exposing the plugin's frontend post editing feature
Sites running third-party plugins or themes that provide exploitable PHP gadget chains

Discovery Timeline

2026-09-02 - CVE-2026-19116 published to the National Vulnerability Database
2026-09-02 - Last updated in NVD database

Technical Details for CVE-2026-19116

Vulnerability Analysis

The User Frontend plugin allows site visitors and members to submit and edit posts through a frontend form. When a previously submitted post is reopened for editing, the plugin retrieves stored custom field values and rehydrates them for the editing interface. During this process, the plugin invokes PHP deserialization on values that originated from user input, rather than treating them as opaque strings.

An authenticated user with the subscriber role or higher can craft a serialized PHP object payload, submit it as a form field value, and then trigger the reopen flow. The unserialize() call instantiates attacker-controlled objects, triggering PHP magic methods such as __wakeup() or __destruct() on any loaded class. When a suitable gadget chain is available in WordPress core, another plugin, or the active theme, the chain can be pivoted into arbitrary file writes, SQL execution, or remote code execution.

Root Cause

The root cause is unsafe deserialization of untrusted input ([CWE-502]). The plugin does not enforce type constraints or use safe encoding formats such as JSON for round-tripping user-supplied field values. Any string that survives storage and reaches the reopen handler is passed to PHP's native deserialization routine without validation.

Attack Vector

Exploitation requires network access to the site and authenticated access at the subscriber tier or above, which is trivial to obtain on sites that allow open registration. The attacker submits a post through the User Frontend form with a serialized object payload embedded in a custom field. They then trigger the reopen action on that submission, causing the plugin to deserialize the payload server-side. See the WPScan Vulnerability Report for additional technical detail.

No public proof-of-concept exploit has been published, and the vulnerability is not listed in the CISA Known Exploited Vulnerabilities catalog.

Detection Methods for CVE-2026-19116

Indicators of Compromise

POST requests to User Frontend submission or edit endpoints containing serialized PHP payload markers such as O:, a:, or s: in field values
Unexpected creation of PHP files, cron entries, or administrator accounts following subscriber activity
PHP error log entries referencing __wakeup, __destruct, or unserialize() originating in the plugin directory
New subscriber-level user registrations followed shortly by frontend post submissions

Detection Strategies

Inspect web server access logs for authenticated subscribers repeatedly invoking the plugin's post edit or reopen endpoints
Review database postmeta rows written by the User Frontend plugin for values beginning with serialized-object prefixes
Correlate WordPress user registration events with subsequent frontend submission activity from the same IP

Monitoring Recommendations

Enable PHP error logging and forward logs to a centralized SIEM for pattern matching on deserialization errors
Monitor file integrity on the wp-content directory to detect unauthorized PHP file drops
Alert on any privilege escalation events, particularly promotion of subscriber accounts to editor or administrator roles

How to Mitigate CVE-2026-19116

Immediate Actions Required

Update the User Frontend WordPress plugin to version 4.3.11 or later on all affected sites
Audit existing user accounts and remove unrecognized subscriber-level registrations
Review recent frontend post submissions for serialized payloads and purge suspicious postmeta records
Rotate WordPress secret keys in wp-config.php and reset administrator credentials if compromise is suspected

Patch Information

The vendor addressed the vulnerability in User Frontend version 4.3.11. The fix prevents user-supplied field values from being deserialized when a submitted post is reopened in the frontend editing form. Refer to the WPScan Vulnerability Report for advisory details.

Workarounds

Disable the User Frontend plugin until the patched version can be deployed
Restrict new user registration or require administrator approval for subscriber accounts
Deploy a web application firewall rule that blocks request bodies containing PHP serialized object patterns targeting the plugin's endpoints
Remove or restrict frontend editing capabilities for low-privilege roles where the feature is not required

bash

# Example WP-CLI commands to update the plugin and audit users
wp plugin update wp-user-frontend --version=4.3.11
wp user list --role=subscriber --fields=ID,user_login,user_registered,user_email
wp option get users_can_register
wp option update users_can_register 0