CVE-2026-66398 affects phpMyFAQ before version 4.1.6 and allows authenticated administrators with CONFIGURATION_EDIT and ATTACHMENT_ADD privileges to achieve remote code execution. The vulnerability arises from the ability to upload a malicious ZIP file as an attachment and then set the upgrade.lastDownloadedPackage configuration to its path. This causes the application to extract the ZIP contents into the application root, enabling arbitrary PHP file writes and execution under the web server user context. No vendor advisory or patch information is currently available, and the vulnerability is rated critical with a CVSS 4.0 score of 9.4.

Successful exploitation allows an authenticated administrator to execute arbitrary PHP code on the server, potentially leading to full compromise of the web application and underlying system privileges granted to the web server user. This can result in unauthorized control over the affected system.

Patch status is not yet confirmed — check the vendor advisory for current remediation guidance. Until an official fix is released, restrict administrator privileges to trusted users only and monitor for suspicious activity related to configuration changes and file uploads.