n8n Ni8mare: critical flaw reachable without login, update self-hosted n8n

In January 2026, n8n published an advisory for CVE-2026-21858, nicknamed Ni8mare by the Cyera researchers who reported it. It is rated 10 out of 10. Through certain form-based workflows, an attacker with no account could read files on the server that runs n8n. Those files can hold the secrets n8n relies on, and Rapid7 explains that the file read can be used to forge an administrator session and go further. Public proof-of-concept code was released the same day, including one that chains this flaw with the code execution flaw CVE-2025-68613 (see our separate alert).

The fix itself had shipped earlier, in n8n 1.121.0 on November 18, 2025, so instances that update regularly were covered before the announcement.

Who is affected

Self-hosted n8n from version 1.65.0 up to, but not including, 1.121.0, especially instances with public forms or webhooks, for example a contact form, a quote request or a chat that feeds a workflow. If you use n8n's hosted cloud service, check your version in the interface or ask n8n support.

How to check your site

Ask your developer whether your forms, chatbots or automations run on n8n, and where it is hosted. Check the n8n version in the interface or in the Docker image tag. If your n8n address opens from anywhere on the internet, consider it exposed.

What to do now

• Update n8n to the latest release. Version 1.121.0 fixes this flaw, but later n8n advisories in 2026 require newer versions (for example 1.123.17 or 2.5.2 for CVE-2026-25049), so do not stop at the minimum.
• If you cannot update right away, the advisory suggests restricting or disabling publicly reachable webhook and form endpoints until you do. There is no official workaround.
• If your instance was outdated and public in 2026, ask your developer to rotate the secrets n8n stores (API keys, connected accounts, email and database passwords) and to review users and workflows for anything unexpected.
• Instances updated since late November 2025 are most likely protected against this flaw, but check the version.

This alert reports what the sources published and is not a guarantee about any specific site.