CVE-2026-39425 is a stored XSS vulnerability in MaxKB (versions < 2.8.0) where the Application prologue field accepts malicious payloads wrapped in <html_rander> tags without proper sanitization or encoding. The backend stores raw HTML/JavaScript in the database via the /admin/api/workspace/{workspace_id}/application endpoint. The frontend then renders this content using an innerHTML-equivalent method, trusting the <html_rander>-wrapped content as safe. This results in persistent DOM-based XSS that can be triggered by any user visiting the affected chatbot interface, allowing attackers to hijack sessions, perform unauthorized actions, and expose sensitive data.

The vulnerability allows authenticated users to inject persistent malicious scripts that execute in the browsers of any users viewing the affected chatbot interface. This can lead to session hijacking, unauthorized operations such as deleting workspaces or applications, and exposure of sensitive information. The CVSS 4.0 score is 5.1 (medium severity), reflecting network attack vector, low complexity, and limited user interaction required.

This issue is fixed in MaxKB version 2.8.0. Users should upgrade to version 2.8.0 or later to remediate this vulnerability. Since the product is not a cloud service, patching the software is required to address the issue. No vendor advisory content contradicts this; therefore, upgrading is the recommended mitigation.