CVE-2026-78278: Fluent Boards Pro IDOR Auth Bypass Flaw

CVE-2026-78278 Overview

CVE-2026-78278 is an Insecure Direct Object Reference (IDOR) vulnerability in the Fluent Boards Pro WordPress plugin through version 2.0.11. The flaw allows authenticated users with Subscriber-level privileges to access resources that should be restricted based on object ownership or role. The issue is tracked under CWE-639: Authorization Bypass Through User-Controlled Key. Because exploitation requires only a low-privileged account and no user interaction, any WordPress site permitting open registration is exposed to unauthorized data access.

Critical Impact
Low-privileged Subscriber accounts can read board resources they do not own by manipulating object identifiers in plugin requests.

Affected Products

Fluent Boards Pro plugin for WordPress
All versions up to and including 2.0.11
WordPress sites permitting Subscriber registration with Fluent Boards Pro installed

Discovery Timeline

2026-08-24 - CVE-2026-78278 published to NVD
2026-08-24 - Last updated in NVD database

Technical Details for CVE-2026-78278

Vulnerability Analysis

The vulnerability is an Insecure Direct Object Reference in Fluent Boards Pro. The plugin exposes endpoints that accept object identifiers (such as board, task, or comment IDs) supplied by the client. The plugin fails to verify whether the requesting user has permission to access the referenced object.

Any authenticated user, including the low-privileged Subscriber role, can iterate or guess object identifiers to retrieve data belonging to other users. The confidentiality impact is limited to information disclosure; integrity and availability are not affected according to the published scoring. The Exploit Prediction Scoring System places this issue in a low likelihood tier at the time of publication.

Root Cause

The root cause is missing authorization checks on plugin request handlers that operate on user-supplied object identifiers. The application trusts the identifier parameter without validating ownership or role-based access rights, which is the defining pattern of CWE-639.

Attack Vector

The attack is executed over the network against the WordPress REST or AJAX interface exposed by Fluent Boards Pro. An attacker registers or obtains a Subscriber account, authenticates, and issues requests that reference object identifiers owned by other users. See the Patchstack Vulnerability Report for advisory details. No public proof-of-concept code has been released.

Detection Methods for CVE-2026-78278

Indicators of Compromise

Authenticated requests from Subscriber-role accounts to Fluent Boards Pro REST or AJAX endpoints referencing object IDs the user does not own.
Sequential or enumerated object identifier values in plugin request parameters, indicating ID iteration.
Unusual volumes of successful HTTP 200 responses to plugin endpoints from a single low-privileged account.

Detection Strategies

Review WordPress access logs for repeated requests to Fluent Boards Pro endpoints (paths containing fluent-boards or fluent_boards) from Subscriber accounts.
Correlate the requesting user ID with the accessed object owner in the plugin database tables to identify cross-user access.
Alert on high-cardinality access to distinct board or task identifiers by a single non-privileged session within a short window.

Monitoring Recommendations

Ingest WordPress and web server logs into a centralized analytics platform and retain them for post-incident review.
Baseline normal plugin request patterns per role and alert on deviations, particularly for Subscriber accounts.
Monitor account registration spikes on sites where open registration is enabled and Fluent Boards Pro is installed.

How to Mitigate CVE-2026-78278

Immediate Actions Required

Upgrade Fluent Boards Pro to a version later than 2.0.11 once the vendor publishes a fixed release.
Disable open user registration on WordPress sites that do not require it by unsetting the Anyone can register option.
Audit existing Subscriber accounts and remove unrecognized or inactive users.

Patch Information

At the time of publication, the Patchstack Vulnerability Report identifies Fluent Boards Pro <= 2.0.11 as affected. Apply the vendor-supplied update as soon as it becomes available and confirm the plugin version is above 2.0.11 after patching.

Workarounds

Restrict access to the WordPress wp-admin and REST endpoints using a Web Application Firewall (WAF) rule set until a patched version is installed.
Temporarily deactivate the Fluent Boards Pro plugin on sites where board data confidentiality is required and no fix is yet applied.
Enforce strong registration controls, such as email verification and CAPTCHA, to reduce automated Subscriber account creation.

bash

# Configuration example: disable open registration via WP-CLI
wp option update users_can_register 0
wp option get users_can_register