n8n: DOM-Based XSS via Unsandboxed iframe srcdoc in HTML Preview

The HTML preview renders execution output into an iframe srcdoc without sandbox, so a sanitizer bypass lets injected script run same-origin as the editor. When a victim opens the preview, it can call authenticated APIs with their session. An account with global:member privileges can exploit it.

The issue has been fixed in n8n versions 1.123.64, 2.29.8, and 2.30.1. Users should upgrade to one of these versions or later to remediate the vulnerability.

If upgrading is not immediately possible, administrators should consider the following temporary mitigations:

• Restrict n8n instance access to fully trusted users only.
• Set the N8N_CONTENT_SECURITY_POLICY environment variable to a policy that blocks inline scripts.
• Avoid exposing workflows that render externally-controlled input into the HTML node or binary HTML preview to untrusted users.

These workarounds do not fully remediate the risk and should only be used as short-term mitigation measures.