CVE-2026-25419: UpsellWP Auth Bypass Vulnerability

CVE-2026-25419 Overview

A Missing Authorization vulnerability has been identified in the flycart UpsellWP WordPress plugin (checkout-upsell-and-order-bumps). This vulnerability allows attackers to exploit incorrectly configured access control security levels, potentially enabling unauthorized access to plugin functionality and sensitive data. The flaw stems from CWE-862 (Missing Authorization), where the plugin fails to properly verify user permissions before allowing access to protected resources.

Critical Impact

Authenticated attackers with low-level privileges can bypass access controls to view sensitive information that should be restricted to administrators, potentially exposing e-commerce configuration data and customer insights.

Affected Products

• UpsellWP WordPress Plugin versions through 2.2.3
• WordPress sites using the checkout-upsell-and-order-bumps plugin
• E-commerce platforms utilizing UpsellWP for checkout optimization

Discovery Timeline

• 2026-02-19 - CVE-2026-25419 published to NVD
• 2026-02-19 - Last updated in NVD database

Technical Details for CVE-2026-25419

Vulnerability Analysis

The vulnerability exists in the UpsellWP plugin due to missing authorization checks on sensitive plugin endpoints and functions. When authenticated users interact with the plugin's functionality, the application fails to verify whether the user has appropriate permissions to perform the requested action. This allows users with minimal privileges (such as subscribers or customers) to access administrative features and view data intended only for site administrators.

The attack requires network access and authentication with at least low-level privileges. Once authenticated, the attacker can exploit the broken access control to read confidential information, though they cannot modify data or cause service disruption through this specific vulnerability.

Root Cause

The root cause is CWE-862 (Missing Authorization). The UpsellWP plugin does not implement proper capability checks or nonce verification on certain AJAX handlers and REST API endpoints. WordPress plugins should use functions like current_user_can() to verify user capabilities before processing sensitive requests, but these checks are absent or improperly implemented in the affected versions.

Attack Vector

The attack is conducted over the network and requires the attacker to have a valid WordPress account on the target site. The exploitation flow involves:

1. Attacker authenticates to the WordPress site with any valid user account (subscriber, customer, etc.)
2. Attacker identifies vulnerable AJAX actions or REST endpoints exposed by the UpsellWP plugin
3. Attacker sends crafted requests to these endpoints without proper authorization headers
4. The plugin processes the request without verifying user capabilities
5. Sensitive data is returned to the unauthorized user

The vulnerability affects the confidentiality of data but does not allow data modification or denial of service. Administrative functions related to upsell configurations, campaign statistics, and potentially customer purchase data may be exposed to unauthorized users.

Detection Methods for CVE-2026-25419

Indicators of Compromise

• Unusual access to UpsellWP AJAX endpoints from non-administrator user sessions
• Multiple requests to plugin REST API endpoints from accounts with subscriber or customer roles
• Access log entries showing authenticated users accessing /wp-admin/admin-ajax.php with UpsellWP-specific action parameters
• Unexpected data access patterns from low-privilege user accounts

Detection Strategies

• Monitor WordPress AJAX request logs for UpsellWP-related actions from non-admin users
• Implement Web Application Firewall (WAF) rules to detect authorization bypass attempts
• Review user activity logs for subscribers accessing administrative plugin functionality
• Audit access patterns to the checkout-upsell-and-order-bumps plugin endpoints

Monitoring Recommendations

• Enable comprehensive logging for all WordPress AJAX and REST API requests
• Configure alerts for access control anomalies involving the UpsellWP plugin
• Regularly audit user roles and permissions on WordPress sites using this plugin
• Deploy endpoint detection solutions to identify unauthorized data access attempts

How to Mitigate CVE-2026-25419

Immediate Actions Required

• Update the UpsellWP plugin to a version newer than 2.2.3 when a patched version becomes available
• Audit user accounts on affected WordPress sites and remove unnecessary privileges
• Review access logs for signs of exploitation prior to patching
• Consider temporarily disabling the UpsellWP plugin until a fix is released

Patch Information

Refer to the Patchstack WordPress Plugin Vulnerability advisory for detailed patch information and vendor updates. Monitor the WordPress plugin repository for updated versions of UpsellWP that address this vulnerability.

Workarounds

• Implement additional access control at the server level using .htaccess or web server configuration
• Use a WordPress security plugin to add capability checks to vulnerable endpoints
• Restrict user registration on affected WordPress sites to reduce attack surface
• Deploy a Web Application Firewall with rules to block unauthorized access attempts to plugin endpoints

# WordPress .htaccess restriction example for plugin admin endpoints
# Add to .htaccess in WordPress root directory
<FilesMatch "admin-ajax\.php$">
    <IfModule mod_rewrite.c>
        RewriteEngine On
        RewriteCond %{REQUEST_METHOD} POST
        RewriteCond %{HTTP:X-Requested-With} !XMLHttpRequest
        RewriteRule .* - [F,L]
    </IfModule>
</FilesMatch>