CVE-2026-65594 is an incorrect authorization vulnerability in n8n's OAuth 2.1 consent and token issuance flow introduced in version 2.27.0. The affected versions (prior to 2.29.8 and 2.30.x before 2.30.1) do not verify that the authenticated user has access rights to the workflow referenced as the OAuth resource. On instances with at least one active MCP Server Trigger workflow configured with n8n OAuth2 authentication, a member-level user can register an OAuth client, self-approve consent for another user's workflow, and obtain a valid token. This token allows the attacker to run the workflow in the owner's project context using the owner's stored credentials, enabling the attacker to set tool inputs and read outputs, potentially exposing data from the owner's connected integrations and violating user and project isolation.

An attacker with member-level access can escalate privileges by obtaining valid OAuth tokens for workflows they do not own. This enables unauthorized execution of workflows in the context of other users, potentially exposing sensitive data from connected integrations and breaking isolation boundaries between users and projects. The vulnerability undermines the security model of n8n's OAuth 2.1 implementation and may lead to data leakage and unauthorized actions within the affected environment.

Patch status is not yet confirmed — check the vendor advisory for current remediation guidance. Until an official fix is released, restrict member-level user permissions to prevent unauthorized OAuth client registration and workflow execution. Monitor for updates from n8n-io regarding patches or official mitigations addressing this vulnerability.