CVE-2026-33749: n8n: stored XSS enables credential theft via workflow

n8n is an open source workflow automation platform. Prior to versions 1.123.27, 2.13.3, and 2.14.1, an authenticated user with permission to create or modify workflows could craft a workflow that produces an HTML binary data object without a filename. The `/rest/binary-data` endpoint served such responses inline on the n8n origin without `Content-Disposition` or `Content-Security-Policy` headers, allowing the HTML to render in the browser with full same-origin JavaScript access. By sending the resulting URL to a higher-privileged user, an attacker could execute JavaScript in the victim's authenticated session, enabling exfiltration of workflows and credentials, modification of workflows, or privilege escalation to admin. The issue has been fixed in n8n versions 1.123.27, 2.13.3, and 2.14.1. 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: Limit workflow creation and editing permissions to fully trusted users only, and/or restrict network access to the n8n instance to prevent untrusted users from accessing binary data URLs. These workarounds do not fully remediate the risk and should only be used as short-term mitigation measures.

An attacker with a low-privilege n8n account (e.g., a contractor, junior dev, or compromised service account) crafts a workflow that generates an HTML payload as a binary output object with no filename. The /rest/binary-data endpoint serves this HTML inline with no Content-Disposition or CSP headers, so the browser renders it as live HTML on the n8n origin. The attacker copies the resulting URL and sends it via Slack/email to an n8n admin ('hey, this workflow output looks broken, can you check?'). When the admin opens the URL in their authenticated browser session, the JavaScript executes with full same-origin access — silently POSTing all stored credentials and workflow definitions to an attacker-controlled endpoint, then creating a backdoor admin account. The admin sees a blank page or error and thinks nothing of it.