CVE-2026-4977: UsersWP WordPress Auth Bypass Vulnerability

CVE-2026-4977 Overview

CVE-2026-4977 is an Improper Access Control vulnerability affecting the UsersWP – Front-end login form, User Registration, User Profile & Members Directory plugin for WordPress in all versions up to and including 1.2.58. The vulnerability exists due to insufficient field-level permission validation in the upload_file_remove() AJAX handler, where the $htmlvar parameter is not validated against a whitelist of allowed fields or checked against the field's for_admin_use property.

This flaw allows authenticated attackers with subscriber-level access and above to clear or reset any restricted usermeta column for their own user record, including fields marked as "For admin use only," effectively bypassing intended field-level access restrictions.

Critical Impact

Authenticated attackers with minimal privileges (subscriber-level) can manipulate restricted user metadata fields, potentially bypassing security controls and modifying admin-only profile data.

Affected Products

• UsersWP – Front-end login form, User Registration, User Profile & Members Directory plugin for WordPress versions up to and including 1.2.58
• WordPress installations using vulnerable UsersWP plugin versions
• Websites relying on UsersWP for user registration and profile management

Discovery Timeline

• 2026-04-10 - CVE-2026-4977 published to NVD
• 2026-04-13 - Last updated in NVD database

Technical Details for CVE-2026-4977

Vulnerability Analysis

This vulnerability is classified as CWE-862 (Missing Authorization). The core issue lies within the upload_file_remove() AJAX handler in the UsersWP plugin's form processing functionality. When processing file removal requests, the handler fails to properly validate whether the requesting user has permission to modify the specified field.

The vulnerable code path can be traced through the class-forms.php file (around lines 2251 and 2274) and the class-meta.php file (around line 165). These locations handle user metadata operations without adequate authorization checks.

The attack requires network access and authentication at the subscriber level, but no user interaction is needed. While the vulnerability allows modification of data integrity, it does not directly impact confidentiality or system availability.

Root Cause

The root cause of CVE-2026-4977 is the absence of proper field-level permission validation in the AJAX handler responsible for file removal operations. Specifically:

1. The $htmlvar parameter passed to the upload_file_remove() function is not validated against a whitelist of fields the authenticated user is permitted to modify
2. The handler does not verify whether the target field has the for_admin_use property set, which should restrict modifications to administrators only
3. This creates a gap where subscribers can manipulate fields that were intended to be editable only by site administrators

Attack Vector

An authenticated attacker with subscriber-level privileges can exploit this vulnerability through the following mechanism:

1. The attacker authenticates to WordPress with a standard subscriber account
2. They craft a malicious AJAX request to the upload_file_remove endpoint
3. By manipulating the $htmlvar parameter, they can target restricted usermeta fields
4. The server processes the request without validating field-level permissions
5. The attacker successfully clears or resets admin-only user metadata for their own account

The vulnerability is exploited via network-based requests to the WordPress AJAX handler. While the attacker can only modify their own user record, this could include clearing sensitive verification flags, approval statuses, or other administrative metadata that controls user capabilities.

For technical details on the vulnerable code paths, refer to the WordPress UsersWP Code Review and the Wordfence Vulnerability Report.

Detection Methods for CVE-2026-4977

Indicators of Compromise

• Unusual AJAX requests to the upload_file_remove action from subscriber-level accounts
• Unexpected modifications to usermeta fields marked as admin-only
• User records showing cleared or reset values in restricted metadata columns
• HTTP POST requests to admin-ajax.php with suspicious $htmlvar parameter values targeting administrative fields

Detection Strategies

• Monitor WordPress AJAX request logs for upload_file_remove actions, particularly from low-privilege users
• Implement database auditing to track changes to usermeta entries, especially those with for_admin_use flags
• Deploy web application firewall (WAF) rules to detect manipulation of the htmlvar parameter targeting restricted fields
• Review access logs for patterns of repeated AJAX requests from subscriber accounts attempting to modify multiple fields

Monitoring Recommendations

• Enable detailed logging for WordPress AJAX handlers to capture full request parameters
• Implement real-time alerts for usermeta modifications made through the UsersWP plugin
• Configure SentinelOne to monitor for suspicious WordPress plugin activity and unauthorized data modifications
• Regularly audit user metadata integrity to identify unauthorized changes to admin-only fields

How to Mitigate CVE-2026-4977

Immediate Actions Required

• Update the UsersWP plugin to version 1.2.59 or later immediately
• Review usermeta records for any unauthorized modifications to admin-only fields
• Audit subscriber accounts for suspicious activity patterns
• Consider temporarily disabling the UsersWP plugin if immediate patching is not possible

Patch Information

The vulnerability has been addressed in UsersWP version 1.2.59. The fix implements proper field-level permission validation in the upload_file_remove() AJAX handler, ensuring that the $htmlvar parameter is checked against allowed fields and the for_admin_use property is respected.

The security patch can be reviewed in the WordPress UsersWP Change Log comparing versions 1.2.58 and 1.2.59.

To update the plugin:

1. Navigate to the WordPress admin panel
2. Go to Plugins → Installed Plugins
3. Locate UsersWP and click "Update Now"
4. Verify the version number is 1.2.59 or higher after update

Workarounds

• Implement additional access control through a security plugin that can filter AJAX requests
• Use a Web Application Firewall (WAF) to block suspicious requests to the upload_file_remove endpoint
• Temporarily disable file upload functionality in UsersWP until the patch is applied
• Restrict subscriber registration if not business-critical until the update is deployed

# Verify current UsersWP plugin version in WordPress
wp plugin list --name=userswp --format=table

# Update UsersWP plugin via WP-CLI
wp plugin update userswp

# Verify the update was successful
wp plugin get userswp --field=version