The vulnerability is a stored cross‑site scripting flaw that occurs when workflow authors set the customCss parameter in a Chat Trigger. Untrusted customCss values are injected into the hosted‑chat page as markup without proper sanitisation. When the chat page is viewed, any malicious script runs with the origin privileges of the n8n instance and can interact with the sessions of visitors who are logged in, potentially hijacking credentials or performing other malicious actions. This represents a web‑based code execution risk confined to the browser context of the instance, not a full‑system compromise.

The flaw affects all versions of n8n prior to 1.123.83, prior to 2.41.4 in the 2.x branch, and prior to 2.42.1 in the 2.42.x branch. The affected product is n8n, the workflow automation platform; any installations running those vulnerable releases are impacted.

With a CVSS score of 7, the flaw is considered high impact. The EPSS score is currently not available, and the vulnerability is not listed in the CISA KEV catalog, suggesting no publicly known exploits at the time of writing. However, the attack vector is simple and accessible from the web interface: workflow authors who can publish a chat trigger without authentication can embed malicious customCss. Because the payload executes in the context of signed‑in users, even non‑authenticated operators could potentially target regular users of the instance, making the risk moderate to high. No external conditions or complex prerequisites are required, increasing the likelihood of exploitation.