n8n before version 2.30.1 allows an authenticated user to request access to any workflow referenced in an OAuth2 request without verifying that the user has permission to act on that workflow; because the OAuth2 consent and token-issuance flow is not checked against the user’s authorization, a member-level attacker can register an OAuth client, self-approve consent for another user’s workflow, obtain a valid token, and use that token to run the workflow within the target’s project context with the target’s stored credentials, thereby setting arbitrary inputs, executing the workflow, and reading outputs that may include sensitive data from the target’s connected integrations, breaking user and project isolation; this weakness aligns with CWE-863, which represents insufficient authorization checks when using credentials.

The vulnerability affects all n8n instances from version 2.27.0 up to, but not including, 2.30.1. It requires at least one active MCP Server Trigger workflow configured with n8n OAuth2 authentication and applies specifically to the n8n product from the vendor n8n‑io, as identified by the CNA.

Assessed CVSS score of 5.1 indicates moderate severity, while the EPSS score of <1% suggests a very low probability of exploitation at this time; the CVE is not listed in CISA's KEV catalog; based on the description, the attack vector is limited to users with at least member-level access on the instance who can register OAuth clients; an attacker can obtain an unauthorized token that permits execution of the target user’s workflow in their project context, allowing read or possibly write access to data from the target’s integrations and thereby compromising user and project isolation.