CVE-2026-39426 MaxKB: Stored XSS via Unsanitized iframe_render Parsing
Attackers can inject malicious scripts via unsanitized iframe tags in AI responses, leading to session hijacking and data exposure for users.
- Exploited in the wild
- Not known
- Login needed
- Any signed-in user
- Attackable
- Over the internet
- Victim action needed
- A user has to click or open something
- Fix
- None listed
What is CVE-2026-39426?
CVE-2026-39426 is a medium-severity cross-site scripting vulnerability in 1Panel-dev MaxKB, published on 14 Apr 2026. Any signed-in user can exploit it over the network, and only if a user opens a file or follows a link.
Official 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.
Weakness: CWE-79
Which versions are affected by CVE-2026-39426?
It affects 1 product.
Products include Maxkb Maxkb.
How do I fix CVE-2026-39426?
No fix has been published for CVE-2026-39426 yet. Limit exposure of the affected software until one is available.
Escape output for the context it lands in and set a strict Content Security Policy. Upgrading the affected component is the real fix. More about Cross-site scripting.
Is CVE-2026-39426 being exploited?
There is no known exploitation of CVE-2026-39426 in the wild and no public exploit code.
Other vulnerabilities in 1Panel-dev MaxKB
- CVE-2025-66419 MaxKB vulnerable to privilege escalation through sandbox bypass
- CVE-2025-66446 MaxKB has a Python sandbox LD_PRELOAD bypass
- CVE-2025-64511 MaxKB has SSRF in sandbox
- CVE-2026-39422 MaxKB has Stored XSS via ChatHeadersMiddleware
- CVE-2026-39423 Stored XSS via Eval Injection in EchartsRander Component
Sources
Also known as GHSA-q2qg-43vq-f2wv.