CVE-2026-75977: Mang Board WP Authentication Bypass Vulnerability

CVE-2026-75977 Overview

CVE-2026-75977 is an authentication cookie forgery flaw in the Mang Board WP plugin for WordPress. The vulnerability affects all versions of the plugin up to and including 2.3.7. Authenticated attackers holding subscriber-level access or higher can forge administrator authentication cookies. The forged cookies allow attackers to change the administrator password and take over the site. The root cause is flawed HMAC generation in the mbw_get_hash_key() function combined with insufficient validation in mbw_validate_auth_cookie(). This weakness maps to [CWE-269: Improper Privilege Management].

Critical Impact
Authenticated subscribers can escalate to administrator, reset admin passwords, and achieve full WordPress site takeover.

Affected Products

Mang Board WP plugin for WordPress, all versions up to and including 2.3.7
WordPress sites running vulnerable versions of the mangboard plugin with at least one logged-in user session
Patched in the plugin release referenced by WordPress Mangboard Change Set 3664567

Discovery Timeline

2026-08-26 - CVE-2026-75977 published to NVD
2026-08-26 - Last updated in NVD database

Technical Details for CVE-2026-75977

Vulnerability Analysis

The Mang Board WP plugin implements its own authentication cookie scheme layered on top of WordPress user sessions. The scheme depends on an HMAC value bound to a specific username. When the HMAC generator sources the wrong username, the resulting cookie can be replayed under any account, including the administrator. Because the plugin's validation routine does not reconcile the cookie's declared username with the HMAC input, forged cookies pass verification. Any authenticated user can then invoke plugin functionality as if they were an administrator and pivot to changing the administrator password. The end result is full compromise of the WordPress installation, including content, users, and installed plugins.

Root Cause

The defect lives in mbw_get_hash_key() inside the plugin's user functions. When a WordPress user is already logged in, the function derives its HMAC key from the current user's identity rather than from the username parameter carried by the cookie. This decouples the HMAC from the identity the cookie claims to represent. The companion function mbw_validate_auth_cookie() then accepts the mismatched cookie because it recomputes the HMAC using the same current-user identity. See the plugin source at WordPress Mangboard Function User and WordPress Mangboard Admin Users.

Attack Vector

The attacker first authenticates to WordPress with any low-privileged account, such as a subscriber. Registration-open sites make this trivial. The attacker then crafts a Mang Board authentication cookie whose username field is set to an administrator account. Because the HMAC is computed against the attacker's own logged-in identity, the cookie validates successfully. With administrator context established inside the plugin, the attacker triggers the plugin's user-management flow to reset the administrator password and log in directly as that administrator.

No public proof-of-concept exploit was listed in the enriched data at the time of publication. Technical details on the vulnerable functions are documented in the Wordfence Vulnerability Report.

Detection Methods for CVE-2026-75977

Indicators of Compromise

Unexpected administrator password changes or new administrator accounts on sites running the Mang Board WP plugin
Requests to Mang Board WP endpoints carrying an mbw-style authentication cookie whose username field references an administrator while the WordPress session cookie belongs to a low-privileged user
Sudden privilege changes in the wp_users and wp_usermeta tables that correlate with authenticated subscriber activity

Detection Strategies

Inventory WordPress installations and flag any site with the mangboard plugin at version 2.3.7 or earlier
Correlate WordPress authentication logs with plugin-level actions to identify subscribers performing administrator-only operations
Alert when a single client session presents WordPress authentication as one user while Mang Board cookies assert a different, higher-privileged user

Monitoring Recommendations

Enable a WordPress audit-logging plugin to capture role changes, password resets, and user creation events
Forward web server access logs to a centralized analytics platform and hunt for anomalous POSTs to plugin endpoints under /wp-admin/admin-ajax.php and /wp-json/
Monitor for outbound requests from the web host that follow administrator takeover, such as installation of unknown plugins or themes

How to Mitigate CVE-2026-75977

Immediate Actions Required

Update the Mang Board WP plugin to the version that includes WordPress Mangboard Change Set 3664567
Rotate all administrator passwords and invalidate active sessions after patching
Review the WordPress user list and remove any unrecognized administrator accounts
Audit recently installed plugins, themes, and modified files for backdoors introduced during the exposure window

Patch Information

The vendor fix is committed in WordPress Mangboard Change Set 3664567, which corrects the HMAC key derivation and cookie validation logic. Administrators should upgrade beyond version 2.3.7 as soon as the patched release is available in the WordPress plugin repository. Verify the installed plugin version in wp-admin under Plugins after the update completes.

Workarounds

Disable and remove the Mang Board WP plugin until it can be upgraded to a fixed release
Restrict new user registration and set the default role to a non-privileged value in WordPress general settings to reduce the attacker pool
Place the WordPress admin area behind an IP allowlist or a web application firewall rule that blocks unauthenticated access to plugin endpoints

bash

# Configuration example: block new registrations and enforce least-privilege default role
wp option update users_can_register 0
wp option update default_role subscriber

# Deactivate and remove the vulnerable plugin until patched
wp plugin deactivate mangboard
wp plugin delete mangboard