CVE-2026-39426: MaxKB: Stored XSS via Unsanitized iframe_render Parsing

Vulnerability summary

CVE-2026-39426 is a medium (CVSS 5.4) vulnerability in 1panel-dev maxkb. EPSS estimates a 0.19% chance of exploitation in the next 30 days, higher than 9% of scored vulnerabilities.

Timeline

1. 14-04-2026
   PublishedVulnerability first disclosed.
2. 16-04-2026
   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 where the frontend's MdRenderer.vue component parses custom <iframe_render> tags from LLM responses or Application Prologue configurations, bypassing standard Markdown sanitization and XSS filtering. The unsanitized HTML content is passed to the IframeRender.vue component, which renders it directly into an <iframe> via the srcdoc attribute configured with sandbox="allow-scripts allow-same-origin". This can be a dangerous combination, allowing injected scripts to escape the iframe and execute JavaScript in the parent window using window.parent. Since the Prologue is rendered for any user visiting an application's chat interface, this results in a high-impact Stored XSS that can lead to session hijacking, unauthorized actions, and sensitive data exposure. This issue has been fixed in version 2.8.0.

• CWE-79Improper Neutralization of Input During Web Page GenerationThe product does not neutralize or incorrectly neutralizes user-controllable input before it is placed in output that is used as a web page that is served to other users.