CVE-2026-15962: Fluent Forms Pro Privilege Escalation Flaw

CVE-2026-15962 Overview

CVE-2026-15962 is a PHP Object Injection vulnerability in the Fluent Forms Pro Add On Pack plugin for WordPress. The flaw affects all versions up to and including 6.2.6 and stems from deserialization of untrusted input [CWE-502]. Authenticated attackers with Subscriber-level access or above can inject a PHP Object. When a Property-Oriented Programming (POP) chain is present, attackers can change user passwords and take over administrator accounts. Exploitation requires that user update integration is enabled and a user meta field is mapped in the plugin configuration.

Critical Impact
Authenticated attackers with minimal privileges can escalate to administrator by injecting serialized PHP objects that trigger password changes via a POP chain.

Affected Products

Fluent Forms Pro Add On Pack plugin for WordPress
All versions up to and including 6.2.6
WordPress sites with user update integration enabled and a user meta field mapped

Discovery Timeline

2026-07-26 - CVE-2026-15962 published to NVD
2026-07-27 - Last updated in NVD database

Technical Details for CVE-2026-15962

Vulnerability Analysis

The Fluent Forms Pro Add On Pack plugin deserializes attacker-controlled input without validating the resulting object graph. PHP's unserialize() function reconstructs objects and invokes magic methods such as __wakeup() and __destruct() during deserialization. Attackers submit crafted serialized payloads through form fields that the plugin passes into the user update integration path. The plugin then processes the payload as user meta content, triggering deserialization on the server. This vulnerability class is tracked as CWE-502: Deserialization of Untrusted Data.

Root Cause

The root cause is the unsafe use of PHP deserialization on data sourced from authenticated form submissions. The plugin trusts the serialized string in mapped user meta fields and does not enforce an allowlist of object types. When a user meta field is mapped through the user update integration, the deserialization path becomes reachable by any authenticated user who can submit the form.

Attack Vector

An attacker authenticates at Subscriber level or higher, which is the default self-registration role on many WordPress sites. The attacker submits a form that maps to a user meta field, embedding a serialized PHP object payload. Fluent Forms Pro Add On Pack deserializes the value on the server side. If a POP chain exists in the WordPress core, plugin, or theme code loaded on the site, the injected object triggers gadget methods that modify user data. Public writeups from Wordfence describe the outcome as password reset for arbitrary users, including administrators, leading to full site takeover. See the Wordfence Vulnerability Report for detailed technical context.

Detection Methods for CVE-2026-15962

Indicators of Compromise

Unexpected password change events for administrator accounts in WordPress audit logs
Form submissions containing serialized PHP payloads with markers such as O:, a:, or s: in fields mapped to user meta
New or elevated user role assignments following a Fluent Forms submission
Outbound web requests from wp-content/plugins/fluentformpro/ at abnormal times

Detection Strategies

Inspect Fluent Forms submission storage and web server logs for payloads matching PHP serialization patterns in user meta mapped fields
Alert on WordPress user_meta and wp_users table writes originating from the plugin outside expected admin workflows
Correlate Subscriber-level authentications with subsequent administrator password resets in the same session

Monitoring Recommendations

Enable WordPress activity logging for user role and password changes with retention of at least 90 days
Forward web server and PHP error logs to a centralized platform and monitor for deserialization exceptions from fluentformpro
Track plugin version inventory across WordPress fleets and flag installations at or below 6.2.6

How to Mitigate CVE-2026-15962

Immediate Actions Required

Update Fluent Forms Pro Add On Pack to a version later than 6.2.6 as soon as a fixed release is available from the vendor
Disable the user update integration in Fluent Forms Pro Add On Pack until patched
Remove user meta field mappings from all active forms as an interim control
Restrict WordPress self-registration or elevate account approval requirements to reduce the pool of Subscriber-level attackers

Patch Information

Consult the FluentForms Official Site and the Wordfence Vulnerability Report for the current fixed version. Apply the vendor-supplied update through the WordPress plugin manager and verify the installed version is above 6.2.6 after upgrade.

Workarounds

Disable the Fluent Forms Pro Add On Pack plugin entirely on sites that do not require it until a patch is applied
Remove or unmap all user meta fields from Fluent Forms form configurations
Apply a web application firewall rule blocking form submissions containing serialized PHP object markers such as O: followed by an integer and a class name
Audit and remove unused plugins and themes to reduce available POP chain gadgets

bash

# Configuration example: disable the plugin from WP-CLI until patched
wp plugin deactivate fluentformpro
wp plugin status fluentformpro