CVE-2026-54804 Overview
CVE-2026-54804 is a broken authentication vulnerability affecting the Melhor Envio WordPress plugin in versions up to and including 2.16.3. The flaw allows authenticated users with Subscriber-level privileges to bypass intended authentication controls within the plugin. Successful exploitation grants attackers access to functionality or data that should be restricted to higher-privileged accounts. The issue is tracked under CWE-288 (Authentication Bypass Using an Alternate Path or Channel) and is documented in the Patchstack Vulnerability Report.
Critical Impact
Authenticated subscribers can bypass authentication checks in the Melhor Envio plugin, leading to integrity loss and potential service disruption on affected WordPress sites.
Affected Products
- Melhor Envio WordPress Plugin (melhor-envio-cotacao)
- All versions up to and including 2.16.3
- WordPress sites with the plugin installed and active
Discovery Timeline
- 2026-06-17 - CVE-2026-54804 published to NVD
- 2026-06-17 - Last updated in NVD database
Technical Details for CVE-2026-54804
Vulnerability Analysis
The vulnerability resides in the authentication logic of the Melhor Envio plugin, a shipping quotation plugin commonly deployed on WooCommerce stores. The plugin fails to enforce proper capability checks on one or more privileged actions. As a result, accounts with the lowest WordPress role tier — Subscriber — can invoke functionality intended only for administrators or shop managers.
The attack surface is reachable over the network and requires only low-privileged authentication. No user interaction is necessary, and exploitation does not depend on social engineering. The impact spans limited confidentiality, limited integrity, and high availability loss on affected WordPress installations.
Root Cause
The root cause is mapped to CWE-288, Authentication Bypass Using an Alternate Path or Channel. The plugin exposes endpoints or AJAX actions that lack current_user_can() checks or rely on weak verification mechanisms. Authenticated subscribers therefore reach code paths that should be gated behind administrator capabilities.
Attack Vector
An attacker registers or compromises a Subscriber-level account on a vulnerable WordPress site. The attacker then issues authenticated HTTP requests against the plugin's exposed endpoints. Because the plugin does not validate the caller's role for privileged operations, the request succeeds. The attacker can alter plugin configuration, tamper with shipping quotation data, or trigger conditions that degrade service availability.
No verified public exploit code is available for this vulnerability. Refer to the Patchstack Vulnerability Report for additional technical context.
Detection Methods for CVE-2026-54804
Indicators of Compromise
- Unexpected HTTP POST requests to admin-ajax.php referencing Melhor Envio actions originating from Subscriber accounts.
- Unauthorized modification of shipping settings, API tokens, or plugin configuration in the WordPress database.
- Newly registered low-privileged accounts followed by privileged plugin actions within a short interval.
Detection Strategies
- Audit WordPress access logs for requests to Melhor Envio endpoints (/wp-admin/admin-ajax.php, plugin REST routes) tied to non-administrative user IDs.
- Review the wp_usermeta and plugin option tables for configuration changes that do not correlate with administrator activity.
- Correlate authentication events with subsequent privileged plugin actions to identify role-mismatch behavior.
Monitoring Recommendations
- Enable verbose logging for the Melhor Envio plugin and forward logs to a centralized SIEM for correlation.
- Alert on Subscriber-role accounts invoking administrative AJAX actions or REST endpoints.
- Monitor WordPress audit trails for changes to shipping configuration, API keys, and integration tokens.
How to Mitigate CVE-2026-54804
Immediate Actions Required
- Update the Melhor Envio plugin to a version later than 2.16.3 once the vendor releases a fixed build.
- Audit existing Subscriber-level accounts and remove any that are unnecessary or unrecognized.
- Disable open user registration on WooCommerce sites unless required for business operations.
Patch Information
Consult the Patchstack Vulnerability Report for fix availability and upgrade guidance. Apply the patched plugin version as soon as it is published in the WordPress plugin repository.
Workarounds
- Deactivate the Melhor Envio plugin until a patched release is available if the site can operate without it.
- Restrict access to wp-admin/admin-ajax.php and plugin REST routes using a Web Application Firewall (WAF) rule scoped to authenticated low-privileged users.
- Temporarily disable new user registrations in WordPress general settings to reduce the attacker's ability to obtain a Subscriber account.
Disclaimer: This content was generated using AI. While we strive for accuracy, please verify critical information with official sources.
