CVE-2026-39425: MaxKB: Stored XSS via Unsanitized html_rander Tags in Markdown Rendering

Vulnerability summary

CVE-2026-39425 is a medium (CVSS 5.4) vulnerability in 1panel-dev maxkb. EPSS estimates a 0.18% chance of exploitation in the next 30 days, higher than 7.6% of scored vulnerabilities.

Timeline

1. 14-04-2026
   PublishedVulnerability first disclosed.
2. 14-04-2026
   Last modifiedVulnerability information updated.

Description

MaxKB is an open-source AI assistant for enterprise. Versions 2.7.1 and below contain a Stored Cross-Site Scripting (XSS) vulnerability that allows authenticated users to inject arbitrary HTML and JavaScript into the Application prologue (Opening Remarks) field by wrapping malicious payloads in <html_rander> tags. The backend fails to sanitize or encode HTML entities in the prologue field when applications are created or updated via the /admin/api/workspace/{workspace_id}/application endpoint, storing the raw payload directly in the database. The frontend then renders this content using an innerHTML-equivalent mechanism, trusting <html_rander>-wrapped content to be safe, which enables persistent DOM-based Stored XSS execution against any visitor who opens the affected chatbot interface. Exploitation can lead to session hijacking, unauthorized actions performed on behalf of victims (such as deleting workspaces or applications), and sensitive data exposure. This issue has been fixed in version 2.8.0.

• CWE-80Improper Neutralization of Script-Related HTML Tags in a Web PageThe product receives input from an upstream component, but it does not neutralize or incorrectly neutralizes special characters such as "<", ">", and "&" that could be interpreted as web-scripting elements when they are sent to a downstream component that processes web pages.